sched/fair: Disable runtime_enabled on dying rq

[mirror_ubuntu-bionic-kernel.git] / kernel / sched / fair.c

/*
 * Completely Fair Scheduling (CFS) Class (SCHED_NORMAL/SCHED_BATCH)
 *
 *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 *  Interactivity improvements by Mike Galbraith
 *  (C) 2007 Mike Galbraith <efault@gmx.de>
 *
 *  Various enhancements by Dmitry Adamushko.
 *  (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com>
 *
 *  Group scheduling enhancements by Srivatsa Vaddagiri
 *  Copyright IBM Corporation, 2007
 *  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
 *
 *  Scaled math optimizations by Thomas Gleixner
 *  Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de>
 *
 *  Adaptive scheduling granularity, math enhancements by Peter Zijlstra
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 */

#include <linux/latencytop.h>
#include <linux/sched.h>
#include <linux/cpumask.h>
#include <linux/slab.h>
#include <linux/profile.h>
#include <linux/interrupt.h>
#include <linux/mempolicy.h>
#include <linux/migrate.h>
#include <linux/task_work.h>

#include <trace/events/sched.h>

#include "sched.h"

/*
 * Targeted preemption latency for CPU-bound tasks:
 * (default: 6ms * (1 + ilog(ncpus)), units: nanoseconds)
 *
 * NOTE: this latency value is not the same as the concept of
 * 'timeslice length' - timeslices in CFS are of variable length
 * and have no persistent notion like in traditional, time-slice
 * based scheduling concepts.
 *
 * (to see the precise effective timeslice length of your workload,
 *  run vmstat and monitor the context-switches (cs) field)
 */
unsigned int sysctl_sched_latency = 6000000ULL;
unsigned int normalized_sysctl_sched_latency = 6000000ULL;

/*
 * The initial- and re-scaling of tunables is configurable
 * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
 *
 * Options are:
 * SCHED_TUNABLESCALING_NONE - unscaled, always *1
 * SCHED_TUNABLESCALING_LOG - scaled logarithmical, *1+ilog(ncpus)
 * SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
 */
enum sched_tunable_scaling sysctl_sched_tunable_scaling
        = SCHED_TUNABLESCALING_LOG;

/*
 * Minimal preemption granularity for CPU-bound tasks:
 * (default: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_min_granularity = 750000ULL;
unsigned int normalized_sysctl_sched_min_granularity = 750000ULL;

/*
 * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
 */
static unsigned int sched_nr_latency = 8;

/*
 * After fork, child runs first. If set to 0 (default) then
 * parent will (try to) run first.
 */
unsigned int sysctl_sched_child_runs_first __read_mostly;

/*
 * SCHED_OTHER wake-up granularity.
 * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
 *
 * This option delays the preemption effects of decoupled workloads
 * and reduces their over-scheduling. Synchronous workloads will still
 * have immediate wakeup/sleep latencies.
 */
unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;

const_debug unsigned int sysctl_sched_migration_cost = 500000UL;

/*
 * The exponential sliding  window over which load is averaged for shares
 * distribution.
 * (default: 10msec)
 */
unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;

#ifdef CONFIG_CFS_BANDWIDTH
/*
 * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
 * each time a cfs_rq requests quota.
 *
 * Note: in the case that the slice exceeds the runtime remaining (either due
 * to consumption or the quota being specified to be smaller than the slice)
 * we will always only issue the remaining available time.
 *
 * default: 5 msec, units: microseconds
  */
unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
#endif

static inline void update_load_add(struct load_weight *lw, unsigned long inc)
{
        lw->weight += inc;
        lw->inv_weight = 0;
}

static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
{
        lw->weight -= dec;
        lw->inv_weight = 0;
}

static inline void update_load_set(struct load_weight *lw, unsigned long w)
{
        lw->weight = w;
        lw->inv_weight = 0;
}

/*
 * Increase the granularity value when there are more CPUs,
 * because with more CPUs the 'effective latency' as visible
 * to users decreases. But the relationship is not linear,
 * so pick a second-best guess by going with the log2 of the
 * number of CPUs.
 *
 * This idea comes from the SD scheduler of Con Kolivas:
 */
static int get_update_sysctl_factor(void)
{
        unsigned int cpus = min_t(int, num_online_cpus(), 8);
        unsigned int factor;

        switch (sysctl_sched_tunable_scaling) {
        case SCHED_TUNABLESCALING_NONE:
                factor = 1;
                break;
        case SCHED_TUNABLESCALING_LINEAR:
                factor = cpus;
                break;
        case SCHED_TUNABLESCALING_LOG:
        default:
                factor = 1 + ilog2(cpus);
                break;
        }

        return factor;
}

static void update_sysctl(void)
{
        unsigned int factor = get_update_sysctl_factor();

#define SET_SYSCTL(name) \
        (sysctl_##name = (factor) * normalized_sysctl_##name)
        SET_SYSCTL(sched_min_granularity);
        SET_SYSCTL(sched_latency);
        SET_SYSCTL(sched_wakeup_granularity);
#undef SET_SYSCTL
}

void sched_init_granularity(void)
{
        update_sysctl();
}

#define WMULT_CONST     (~0U)
#define WMULT_SHIFT     32

static void __update_inv_weight(struct load_weight *lw)
{
        unsigned long w;

        if (likely(lw->inv_weight))
                return;

        w = scale_load_down(lw->weight);

        if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
                lw->inv_weight = 1;
        else if (unlikely(!w))
                lw->inv_weight = WMULT_CONST;
        else
                lw->inv_weight = WMULT_CONST / w;
}

/*
 * delta_exec * weight / lw.weight
 *   OR
 * (delta_exec * (weight * lw->inv_weight)) >> WMULT_SHIFT
 *
 * Either weight := NICE_0_LOAD and lw \e prio_to_wmult[], in which case
 * we're guaranteed shift stays positive because inv_weight is guaranteed to
 * fit 32 bits, and NICE_0_LOAD gives another 10 bits; therefore shift >= 22.
 *
 * Or, weight =< lw.weight (because lw.weight is the runqueue weight), thus
 * weight/lw.weight <= 1, and therefore our shift will also be positive.
 */
static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
{
        u64 fact = scale_load_down(weight);
        int shift = WMULT_SHIFT;

        __update_inv_weight(lw);

        if (unlikely(fact >> 32)) {
                while (fact >> 32) {
                        fact >>= 1;
                        shift--;
                }
        }

        /* hint to use a 32x32->64 mul */
        fact = (u64)(u32)fact * lw->inv_weight;

        while (fact >> 32) {
                fact >>= 1;
                shift--;
        }

        return mul_u64_u32_shr(delta_exec, fact, shift);
}


const struct sched_class fair_sched_class;

/**************************************************************
 * CFS operations on generic schedulable entities:
 */

#ifdef CONFIG_FAIR_GROUP_SCHED

/* cpu runqueue to which this cfs_rq is attached */
static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
        return cfs_rq->rq;
}

/* An entity is a task if it doesn't "own" a runqueue */
#define entity_is_task(se)      (!se->my_q)

static inline struct task_struct *task_of(struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
        WARN_ON_ONCE(!entity_is_task(se));
#endif
        return container_of(se, struct task_struct, se);
}

/* Walk up scheduling entities hierarchy */
#define for_each_sched_entity(se) \
                for (; se; se = se->parent)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
        return p->se.cfs_rq;
}

/* runqueue on which this entity is (to be) queued */
static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
        return se->cfs_rq;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
        return grp->my_q;
}

static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
                                       int force_update);

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (!cfs_rq->on_list) {
                /*
                 * Ensure we either appear before our parent (if already
                 * enqueued) or force our parent to appear after us when it is
                 * enqueued.  The fact that we always enqueue bottom-up
                 * reduces this to two cases.
                 */
                if (cfs_rq->tg->parent &&
                    cfs_rq->tg->parent->cfs_rq[cpu_of(rq_of(cfs_rq))]->on_list) {
                        list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &rq_of(cfs_rq)->leaf_cfs_rq_list);
                } else {
                        list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &rq_of(cfs_rq)->leaf_cfs_rq_list);
                }

                cfs_rq->on_list = 1;
                /* We should have no load, but we need to update last_decay. */
                update_cfs_rq_blocked_load(cfs_rq, 0);
        }
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (cfs_rq->on_list) {
                list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
                cfs_rq->on_list = 0;
        }
}

/* Iterate thr' all leaf cfs_rq's on a runqueue */
#define for_each_leaf_cfs_rq(rq, cfs_rq) \
        list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)

/* Do the two (enqueued) entities belong to the same group ? */
static inline struct cfs_rq *
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        if (se->cfs_rq == pse->cfs_rq)
                return se->cfs_rq;

        return NULL;
}

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
        return se->parent;
}

static void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
        int se_depth, pse_depth;

        /*
         * preemption test can be made between sibling entities who are in the
         * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
         * both tasks until we find their ancestors who are siblings of common
         * parent.
         */

        /* First walk up until both entities are at same depth */
        se_depth = (*se)->depth;
        pse_depth = (*pse)->depth;

        while (se_depth > pse_depth) {
                se_depth--;
                *se = parent_entity(*se);
        }

        while (pse_depth > se_depth) {
                pse_depth--;
                *pse = parent_entity(*pse);
        }

        while (!is_same_group(*se, *pse)) {
                *se = parent_entity(*se);
                *pse = parent_entity(*pse);
        }
}

#else   /* !CONFIG_FAIR_GROUP_SCHED */

static inline struct task_struct *task_of(struct sched_entity *se)
{
        return container_of(se, struct task_struct, se);
}

static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
        return container_of(cfs_rq, struct rq, cfs);
}

#define entity_is_task(se)      1

#define for_each_sched_entity(se) \
                for (; se; se = NULL)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
        return &task_rq(p)->cfs;
}

static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
        struct task_struct *p = task_of(se);
        struct rq *rq = task_rq(p);

        return &rq->cfs;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
        return NULL;
}

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

#define for_each_leaf_cfs_rq(rq, cfs_rq) \
                for (cfs_rq = &rq->cfs; cfs_rq; cfs_rq = NULL)

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
        return NULL;
}

static inline void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
}

#endif  /* CONFIG_FAIR_GROUP_SCHED */

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);

/**************************************************************
 * Scheduling class tree data structure manipulation methods:
 */

static inline u64 max_vruntime(u64 max_vruntime, u64 vruntime)
{
        s64 delta = (s64)(vruntime - max_vruntime);
        if (delta > 0)
                max_vruntime = vruntime;

        return max_vruntime;
}

static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
{
        s64 delta = (s64)(vruntime - min_vruntime);
        if (delta < 0)
                min_vruntime = vruntime;

        return min_vruntime;
}

static inline int entity_before(struct sched_entity *a,
                                struct sched_entity *b)
{
        return (s64)(a->vruntime - b->vruntime) < 0;
}

static void update_min_vruntime(struct cfs_rq *cfs_rq)
{
        u64 vruntime = cfs_rq->min_vruntime;

        if (cfs_rq->curr)
                vruntime = cfs_rq->curr->vruntime;

        if (cfs_rq->rb_leftmost) {
                struct sched_entity *se = rb_entry(cfs_rq->rb_leftmost,
                                                   struct sched_entity,
                                                   run_node);

                if (!cfs_rq->curr)
                        vruntime = se->vruntime;
                else
                        vruntime = min_vruntime(vruntime, se->vruntime);
        }

        /* ensure we never gain time by being placed backwards. */
        cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
#ifndef CONFIG_64BIT
        smp_wmb();
        cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
}

/*
 * Enqueue an entity into the rb-tree:
 */
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct rb_node **link = &cfs_rq->tasks_timeline.rb_node;
        struct rb_node *parent = NULL;
        struct sched_entity *entry;
        int leftmost = 1;

        /*
         * Find the right place in the rbtree:
         */
        while (*link) {
                parent = *link;
                entry = rb_entry(parent, struct sched_entity, run_node);
                /*
                 * We dont care about collisions. Nodes with
                 * the same key stay together.
                 */
                if (entity_before(se, entry)) {
                        link = &parent->rb_left;
                } else {
                        link = &parent->rb_right;
                        leftmost = 0;
                }
        }

        /*
         * Maintain a cache of leftmost tree entries (it is frequently
         * used):
         */
        if (leftmost)
                cfs_rq->rb_leftmost = &se->run_node;

        rb_link_node(&se->run_node, parent, link);
        rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
}

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (cfs_rq->rb_leftmost == &se->run_node) {
                struct rb_node *next_node;

                next_node = rb_next(&se->run_node);
                cfs_rq->rb_leftmost = next_node;
        }

        rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
}

struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *left = cfs_rq->rb_leftmost;

        if (!left)
                return NULL;

        return rb_entry(left, struct sched_entity, run_node);
}

static struct sched_entity *__pick_next_entity(struct sched_entity *se)
{
        struct rb_node *next = rb_next(&se->run_node);

        if (!next)
                return NULL;

        return rb_entry(next, struct sched_entity, run_node);
}

#ifdef CONFIG_SCHED_DEBUG
struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *last = rb_last(&cfs_rq->tasks_timeline);

        if (!last)
                return NULL;

        return rb_entry(last, struct sched_entity, run_node);
}

/**************************************************************
 * Scheduling class statistics methods:
 */

int sched_proc_update_handler(struct ctl_table *table, int write,
                void __user *buffer, size_t *lenp,
                loff_t *ppos)
{
        int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
        int factor = get_update_sysctl_factor();

        if (ret || !write)
                return ret;

        sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
                                        sysctl_sched_min_granularity);

#define WRT_SYSCTL(name) \
        (normalized_sysctl_##name = sysctl_##name / (factor))
        WRT_SYSCTL(sched_min_granularity);
        WRT_SYSCTL(sched_latency);
        WRT_SYSCTL(sched_wakeup_granularity);
#undef WRT_SYSCTL

        return 0;
}
#endif

/*
 * delta /= w
 */
static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
{
        if (unlikely(se->load.weight != NICE_0_LOAD))
                delta = __calc_delta(delta, NICE_0_LOAD, &se->load);

        return delta;
}

/*
 * The idea is to set a period in which each task runs once.
 *
 * When there are too many tasks (sched_nr_latency) we have to stretch
 * this period because otherwise the slices get too small.
 *
 * p = (nr <= nl) ? l : l*nr/nl
 */
static u64 __sched_period(unsigned long nr_running)
{
        u64 period = sysctl_sched_latency;
        unsigned long nr_latency = sched_nr_latency;

        if (unlikely(nr_running > nr_latency)) {
                period = sysctl_sched_min_granularity;
                period *= nr_running;
        }

        return period;
}

/*
 * We calculate the wall-time slice from the period by taking a part
 * proportional to the weight.
 *
 * s = p*P[w/rw]
 */
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);

        for_each_sched_entity(se) {
                struct load_weight *load;
                struct load_weight lw;

                cfs_rq = cfs_rq_of(se);
                load = &cfs_rq->load;

                if (unlikely(!se->on_rq)) {
                        lw = cfs_rq->load;

                        update_load_add(&lw, se->load.weight);
                        load = &lw;
                }
                slice = __calc_delta(slice, se->load.weight, load);
        }
        return slice;
}

/*
 * We calculate the vruntime slice of a to-be-inserted task.
 *
 * vs = s/w
 */
static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        return calc_delta_fair(sched_slice(cfs_rq, se), se);
}

#ifdef CONFIG_SMP
static unsigned long task_h_load(struct task_struct *p);

static inline void __update_task_entity_contrib(struct sched_entity *se);

/* Give new task start runnable values to heavy its load in infant time */
void init_task_runnable_average(struct task_struct *p)
{
        u32 slice;

        p->se.avg.decay_count = 0;
        slice = sched_slice(task_cfs_rq(p), &p->se) >> 10;
        p->se.avg.runnable_avg_sum = slice;
        p->se.avg.runnable_avg_period = slice;
        __update_task_entity_contrib(&p->se);
}
#else
void init_task_runnable_average(struct task_struct *p)
{
}
#endif

/*
 * Update the current task's runtime statistics.
 */
static void update_curr(struct cfs_rq *cfs_rq)
{
        struct sched_entity *curr = cfs_rq->curr;
        u64 now = rq_clock_task(rq_of(cfs_rq));
        u64 delta_exec;

        if (unlikely(!curr))
                return;

        delta_exec = now - curr->exec_start;
        if (unlikely((s64)delta_exec <= 0))
                return;

        curr->exec_start = now;

        schedstat_set(curr->statistics.exec_max,
                      max(delta_exec, curr->statistics.exec_max));

        curr->sum_exec_runtime += delta_exec;
        schedstat_add(cfs_rq, exec_clock, delta_exec);

        curr->vruntime += calc_delta_fair(delta_exec, curr);
        update_min_vruntime(cfs_rq);

        if (entity_is_task(curr)) {
                struct task_struct *curtask = task_of(curr);

                trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
                cpuacct_charge(curtask, delta_exec);
                account_group_exec_runtime(curtask, delta_exec);
        }

        account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static inline void
update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        schedstat_set(se->statistics.wait_start, rq_clock(rq_of(cfs_rq)));
}

/*
 * Task is being enqueued - update stats:
 */
static void update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * Are we enqueueing a waiting task? (for current tasks
         * a dequeue/enqueue event is a NOP)
         */
        if (se != cfs_rq->curr)
                update_stats_wait_start(cfs_rq, se);
}

static void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        schedstat_set(se->statistics.wait_max, max(se->statistics.wait_max,
                        rq_clock(rq_of(cfs_rq)) - se->statistics.wait_start));
        schedstat_set(se->statistics.wait_count, se->statistics.wait_count + 1);
        schedstat_set(se->statistics.wait_sum, se->statistics.wait_sum +
                        rq_clock(rq_of(cfs_rq)) - se->statistics.wait_start);
#ifdef CONFIG_SCHEDSTATS
        if (entity_is_task(se)) {
                trace_sched_stat_wait(task_of(se),
                        rq_clock(rq_of(cfs_rq)) - se->statistics.wait_start);
        }
#endif
        schedstat_set(se->statistics.wait_start, 0);
}

static inline void
update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * Mark the end of the wait period if dequeueing a
         * waiting task:
         */
        if (se != cfs_rq->curr)
                update_stats_wait_end(cfs_rq, se);
}

/*
 * We are picking a new current task - update its stats:
 */
static inline void
update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * We are starting a new run period:
         */
        se->exec_start = rq_clock_task(rq_of(cfs_rq));
}

/**************************************************
 * Scheduling class queueing methods:
 */

#ifdef CONFIG_NUMA_BALANCING
/*
 * Approximate time to scan a full NUMA task in ms. The task scan period is
 * calculated based on the tasks virtual memory size and
 * numa_balancing_scan_size.
 */
unsigned int sysctl_numa_balancing_scan_period_min = 1000;
unsigned int sysctl_numa_balancing_scan_period_max = 60000;

/* Portion of address space to scan in MB */
unsigned int sysctl_numa_balancing_scan_size = 256;

/* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
unsigned int sysctl_numa_balancing_scan_delay = 1000;

static unsigned int task_nr_scan_windows(struct task_struct *p)
{
        unsigned long rss = 0;
        unsigned long nr_scan_pages;

        /*
         * Calculations based on RSS as non-present and empty pages are skipped
         * by the PTE scanner and NUMA hinting faults should be trapped based
         * on resident pages
         */
        nr_scan_pages = sysctl_numa_balancing_scan_size << (20 - PAGE_SHIFT);
        rss = get_mm_rss(p->mm);
        if (!rss)
                rss = nr_scan_pages;

        rss = round_up(rss, nr_scan_pages);
        return rss / nr_scan_pages;
}

/* For sanitys sake, never scan more PTEs than MAX_SCAN_WINDOW MB/sec. */
#define MAX_SCAN_WINDOW 2560

static unsigned int task_scan_min(struct task_struct *p)
{
        unsigned int scan, floor;
        unsigned int windows = 1;

        if (sysctl_numa_balancing_scan_size < MAX_SCAN_WINDOW)
                windows = MAX_SCAN_WINDOW / sysctl_numa_balancing_scan_size;
        floor = 1000 / windows;

        scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
        return max_t(unsigned int, floor, scan);
}

static unsigned int task_scan_max(struct task_struct *p)
{
        unsigned int smin = task_scan_min(p);
        unsigned int smax;

        /* Watch for min being lower than max due to floor calculations */
        smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);
        return max(smin, smax);
}

static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
        rq->nr_numa_running += (p->numa_preferred_nid != -1);
        rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
}

static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
        rq->nr_numa_running -= (p->numa_preferred_nid != -1);
        rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
}

struct numa_group {
        atomic_t refcount;

        spinlock_t lock; /* nr_tasks, tasks */
        int nr_tasks;
        pid_t gid;
        struct list_head task_list;

        struct rcu_head rcu;
        nodemask_t active_nodes;
        unsigned long total_faults;
        /*
         * Faults_cpu is used to decide whether memory should move
         * towards the CPU. As a consequence, these stats are weighted
         * more by CPU use than by memory faults.
         */
        unsigned long *faults_cpu;
        unsigned long faults[0];
};

/* Shared or private faults. */
#define NR_NUMA_HINT_FAULT_TYPES 2

/* Memory and CPU locality */
#define NR_NUMA_HINT_FAULT_STATS (NR_NUMA_HINT_FAULT_TYPES * 2)

/* Averaged statistics, and temporary buffers. */
#define NR_NUMA_HINT_FAULT_BUCKETS (NR_NUMA_HINT_FAULT_STATS * 2)

pid_t task_numa_group_id(struct task_struct *p)
{
        return p->numa_group ? p->numa_group->gid : 0;
}

static inline int task_faults_idx(int nid, int priv)
{
        return NR_NUMA_HINT_FAULT_TYPES * nid + priv;
}

static inline unsigned long task_faults(struct task_struct *p, int nid)
{
        if (!p->numa_faults_memory)
                return 0;

        return p->numa_faults_memory[task_faults_idx(nid, 0)] +
                p->numa_faults_memory[task_faults_idx(nid, 1)];
}

static inline unsigned long group_faults(struct task_struct *p, int nid)
{
        if (!p->numa_group)
                return 0;

        return p->numa_group->faults[task_faults_idx(nid, 0)] +
                p->numa_group->faults[task_faults_idx(nid, 1)];
}

static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
{
        return group->faults_cpu[task_faults_idx(nid, 0)] +
                group->faults_cpu[task_faults_idx(nid, 1)];
}

/*
 * These return the fraction of accesses done by a particular task, or
 * task group, on a particular numa node.  The group weight is given a
 * larger multiplier, in order to group tasks together that are almost
 * evenly spread out between numa nodes.
 */
static inline unsigned long task_weight(struct task_struct *p, int nid)
{
        unsigned long total_faults;

        if (!p->numa_faults_memory)
                return 0;

        total_faults = p->total_numa_faults;

        if (!total_faults)
                return 0;

        return 1000 * task_faults(p, nid) / total_faults;
}

static inline unsigned long group_weight(struct task_struct *p, int nid)
{
        if (!p->numa_group || !p->numa_group->total_faults)
                return 0;

        return 1000 * group_faults(p, nid) / p->numa_group->total_faults;
}

bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
                                int src_nid, int dst_cpu)
{
        struct numa_group *ng = p->numa_group;
        int dst_nid = cpu_to_node(dst_cpu);
        int last_cpupid, this_cpupid;

        this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);

        /*
         * Multi-stage node selection is used in conjunction with a periodic
         * migration fault to build a temporal task<->page relation. By using
         * a two-stage filter we remove short/unlikely relations.
         *
         * Using P(p) ~ n_p / n_t as per frequentist probability, we can equate
         * a task's usage of a particular page (n_p) per total usage of this
         * page (n_t) (in a given time-span) to a probability.
         *
         * Our periodic faults will sample this probability and getting the
         * same result twice in a row, given these samples are fully
         * independent, is then given by P(n)^2, provided our sample period
         * is sufficiently short compared to the usage pattern.
         *
         * This quadric squishes small probabilities, making it less likely we
         * act on an unlikely task<->page relation.
         */
        last_cpupid = page_cpupid_xchg_last(page, this_cpupid);
        if (!cpupid_pid_unset(last_cpupid) &&
                                cpupid_to_nid(last_cpupid) != dst_nid)
                return false;

        /* Always allow migrate on private faults */
        if (cpupid_match_pid(p, last_cpupid))
                return true;

        /* A shared fault, but p->numa_group has not been set up yet. */
        if (!ng)
                return true;

        /*
         * Do not migrate if the destination is not a node that
         * is actively used by this numa group.
         */
        if (!node_isset(dst_nid, ng->active_nodes))
                return false;

        /*
         * Source is a node that is not actively used by this
         * numa group, while the destination is. Migrate.
         */
        if (!node_isset(src_nid, ng->active_nodes))
                return true;

        /*
         * Both source and destination are nodes in active
         * use by this numa group. Maximize memory bandwidth
         * by migrating from more heavily used groups, to less
         * heavily used ones, spreading the load around.
         * Use a 1/4 hysteresis to avoid spurious page movement.
         */
        return group_faults(p, dst_nid) < (group_faults(p, src_nid) * 3 / 4);
}

static unsigned long weighted_cpuload(const int cpu);
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);
static unsigned long capacity_of(int cpu);
static long effective_load(struct task_group *tg, int cpu, long wl, long wg);

/* Cached statistics for all CPUs within a node */
struct numa_stats {
        unsigned long nr_running;
        unsigned long load;

        /* Total compute capacity of CPUs on a node */
        unsigned long compute_capacity;

        /* Approximate capacity in terms of runnable tasks on a node */
        unsigned long task_capacity;
        int has_free_capacity;
};

/*
 * XXX borrowed from update_sg_lb_stats
 */
static void update_numa_stats(struct numa_stats *ns, int nid)
{
        int cpu, cpus = 0;

        memset(ns, 0, sizeof(*ns));
        for_each_cpu(cpu, cpumask_of_node(nid)) {
                struct rq *rq = cpu_rq(cpu);

                ns->nr_running += rq->nr_running;
                ns->load += weighted_cpuload(cpu);
                ns->compute_capacity += capacity_of(cpu);

                cpus++;
        }

        /*
         * If we raced with hotplug and there are no CPUs left in our mask
         * the @ns structure is NULL'ed and task_numa_compare() will
         * not find this node attractive.
         *
         * We'll either bail at !has_free_capacity, or we'll detect a huge
         * imbalance and bail there.
         */
        if (!cpus)
                return;

        ns->task_capacity =
                DIV_ROUND_CLOSEST(ns->compute_capacity, SCHED_CAPACITY_SCALE);
        ns->has_free_capacity = (ns->nr_running < ns->task_capacity);
}

struct task_numa_env {
        struct task_struct *p;

        int src_cpu, src_nid;
        int dst_cpu, dst_nid;

        struct numa_stats src_stats, dst_stats;

        int imbalance_pct;

        struct task_struct *best_task;
        long best_imp;
        int best_cpu;
};

static void task_numa_assign(struct task_numa_env *env,
                             struct task_struct *p, long imp)
{
        if (env->best_task)
                put_task_struct(env->best_task);
        if (p)
                get_task_struct(p);

        env->best_task = p;
        env->best_imp = imp;
        env->best_cpu = env->dst_cpu;
}

static bool load_too_imbalanced(long src_load, long dst_load,
                                struct task_numa_env *env)
{
        long imb, old_imb;
        long orig_src_load, orig_dst_load;
        long src_capacity, dst_capacity;

        /*
         * The load is corrected for the CPU capacity available on each node.
         *
         * src_load        dst_load
         * ------------ vs ---------
         * src_capacity    dst_capacity
         */
        src_capacity = env->src_stats.compute_capacity;
        dst_capacity = env->dst_stats.compute_capacity;

        /* We care about the slope of the imbalance, not the direction. */
        if (dst_load < src_load)
                swap(dst_load, src_load);

        /* Is the difference below the threshold? */
        imb = dst_load * src_capacity * 100 -
              src_load * dst_capacity * env->imbalance_pct;
        if (imb <= 0)
                return false;

        /*
         * The imbalance is above the allowed threshold.
         * Compare it with the old imbalance.
         */
        orig_src_load = env->src_stats.load;
        orig_dst_load = env->dst_stats.load;

        if (orig_dst_load < orig_src_load)
                swap(orig_dst_load, orig_src_load);

        old_imb = orig_dst_load * src_capacity * 100 -
                  orig_src_load * dst_capacity * env->imbalance_pct;

        /* Would this change make things worse? */
        return (imb > old_imb);
}

/*
 * This checks if the overall compute and NUMA accesses of the system would
 * be improved if the source tasks was migrated to the target dst_cpu taking
 * into account that it might be best if task running on the dst_cpu should
 * be exchanged with the source task
 */
static void task_numa_compare(struct task_numa_env *env,
                              long taskimp, long groupimp)
{
        struct rq *src_rq = cpu_rq(env->src_cpu);
        struct rq *dst_rq = cpu_rq(env->dst_cpu);
        struct task_struct *cur;
        struct task_group *tg;
        long src_load, dst_load;
        long load;
        long imp = env->p->numa_group ? groupimp : taskimp;
        long moveimp = imp;

        rcu_read_lock();
        cur = ACCESS_ONCE(dst_rq->curr);
        if (cur->pid == 0) /* idle */
                cur = NULL;

        /*
         * "imp" is the fault differential for the source task between the
         * source and destination node. Calculate the total differential for
         * the source task and potential destination task. The more negative
         * the value is, the more rmeote accesses that would be expected to
         * be incurred if the tasks were swapped.
         */
        if (cur) {
                /* Skip this swap candidate if cannot move to the source cpu */
                if (!cpumask_test_cpu(env->src_cpu, tsk_cpus_allowed(cur)))
                        goto unlock;

                /*
                 * If dst and source tasks are in the same NUMA group, or not
                 * in any group then look only at task weights.
                 */
                if (cur->numa_group == env->p->numa_group) {
                        imp = taskimp + task_weight(cur, env->src_nid) -
                              task_weight(cur, env->dst_nid);
                        /*
                         * Add some hysteresis to prevent swapping the
                         * tasks within a group over tiny differences.
                         */
                        if (cur->numa_group)
                                imp -= imp/16;
                } else {
                        /*
                         * Compare the group weights. If a task is all by
                         * itself (not part of a group), use the task weight
                         * instead.
                         */
                        if (cur->numa_group)
                                imp += group_weight(cur, env->src_nid) -
                                       group_weight(cur, env->dst_nid);
                        else
                                imp += task_weight(cur, env->src_nid) -
                                       task_weight(cur, env->dst_nid);
                }
        }

        if (imp <= env->best_imp && moveimp <= env->best_imp)
                goto unlock;

        if (!cur) {
                /* Is there capacity at our destination? */
                if (env->src_stats.has_free_capacity &&
                    !env->dst_stats.has_free_capacity)
                        goto unlock;

                goto balance;
        }

        /* Balance doesn't matter much if we're running a task per cpu */
        if (imp > env->best_imp && src_rq->nr_running == 1 &&
                        dst_rq->nr_running == 1)
                goto assign;

        /*
         * In the overloaded case, try and keep the load balanced.
         */
balance:
        src_load = env->src_stats.load;
        dst_load = env->dst_stats.load;

        /* Calculate the effect of moving env->p from src to dst. */
        load = env->p->se.load.weight;
        tg = task_group(env->p);
        src_load += effective_load(tg, env->src_cpu, -load, -load);
        dst_load += effective_load(tg, env->dst_cpu, load, load);

        if (moveimp > imp && moveimp > env->best_imp) {
                /*
                 * If the improvement from just moving env->p direction is
                 * better than swapping tasks around, check if a move is
                 * possible. Store a slightly smaller score than moveimp,
                 * so an actually idle CPU will win.
                 */
                if (!load_too_imbalanced(src_load, dst_load, env)) {
                        imp = moveimp - 1;
                        cur = NULL;
                        goto assign;
                }
        }

        if (imp <= env->best_imp)
                goto unlock;

        if (cur) {
                /* Cur moves in the opposite direction. */
                load = cur->se.load.weight;
                tg = task_group(cur);
                src_load += effective_load(tg, env->src_cpu, load, load);
                dst_load += effective_load(tg, env->dst_cpu, -load, -load);
        }

        if (load_too_imbalanced(src_load, dst_load, env))
                goto unlock;

assign:
        task_numa_assign(env, cur, imp);
unlock:
        rcu_read_unlock();
}

static void task_numa_find_cpu(struct task_numa_env *env,
                                long taskimp, long groupimp)
{
        int cpu;

        for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
                /* Skip this CPU if the source task cannot migrate */
                if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)))
                        continue;

                env->dst_cpu = cpu;
                task_numa_compare(env, taskimp, groupimp);
        }
}

static int task_numa_migrate(struct task_struct *p)
{
        struct task_numa_env env = {
                .p = p,

                .src_cpu = task_cpu(p),
                .src_nid = task_node(p),

                .imbalance_pct = 112,

                .best_task = NULL,
                .best_imp = 0,
                .best_cpu = -1
        };
        struct sched_domain *sd;
        unsigned long taskweight, groupweight;
        int nid, ret;
        long taskimp, groupimp;

        /*
         * Pick the lowest SD_NUMA domain, as that would have the smallest
         * imbalance and would be the first to start moving tasks about.
         *
         * And we want to avoid any moving of tasks about, as that would create
         * random movement of tasks -- counter the numa conditions we're trying
         * to satisfy here.
         */
        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
        if (sd)
                env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
        rcu_read_unlock();

        /*
         * Cpusets can break the scheduler domain tree into smaller
         * balance domains, some of which do not cross NUMA boundaries.
         * Tasks that are "trapped" in such domains cannot be migrated
         * elsewhere, so there is no point in (re)trying.
         */
        if (unlikely(!sd)) {
                p->numa_preferred_nid = task_node(p);
                return -EINVAL;
        }

        taskweight = task_weight(p, env.src_nid);
        groupweight = group_weight(p, env.src_nid);
        update_numa_stats(&env.src_stats, env.src_nid);
        env.dst_nid = p->numa_preferred_nid;
        taskimp = task_weight(p, env.dst_nid) - taskweight;
        groupimp = group_weight(p, env.dst_nid) - groupweight;
        update_numa_stats(&env.dst_stats, env.dst_nid);

        /* Try to find a spot on the preferred nid. */
        task_numa_find_cpu(&env, taskimp, groupimp);

        /* No space available on the preferred nid. Look elsewhere. */
        if (env.best_cpu == -1) {
                for_each_online_node(nid) {
                        if (nid == env.src_nid || nid == p->numa_preferred_nid)
                                continue;

                        /* Only consider nodes where both task and groups benefit */
                        taskimp = task_weight(p, nid) - taskweight;
                        groupimp = group_weight(p, nid) - groupweight;
                        if (taskimp < 0 && groupimp < 0)
                                continue;

                        env.dst_nid = nid;
                        update_numa_stats(&env.dst_stats, env.dst_nid);
                        task_numa_find_cpu(&env, taskimp, groupimp);
                }
        }

        /*
         * If the task is part of a workload that spans multiple NUMA nodes,
         * and is migrating into one of the workload's active nodes, remember
         * this node as the task's preferred numa node, so the workload can
         * settle down.
         * A task that migrated to a second choice node will be better off
         * trying for a better one later. Do not set the preferred node here.
         */
        if (p->numa_group) {
                if (env.best_cpu == -1)
                        nid = env.src_nid;
                else
                        nid = env.dst_nid;

                if (node_isset(nid, p->numa_group->active_nodes))
                        sched_setnuma(p, env.dst_nid);
        }

        /* No better CPU than the current one was found. */
        if (env.best_cpu == -1)
                return -EAGAIN;

        /*
         * Reset the scan period if the task is being rescheduled on an
         * alternative node to recheck if the tasks is now properly placed.
         */
        p->numa_scan_period = task_scan_min(p);

        if (env.best_task == NULL) {
                ret = migrate_task_to(p, env.best_cpu);
                if (ret != 0)
                        trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
                return ret;
        }

        ret = migrate_swap(p, env.best_task);
        if (ret != 0)
                trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
        put_task_struct(env.best_task);
        return ret;
}

/* Attempt to migrate a task to a CPU on the preferred node. */
static void numa_migrate_preferred(struct task_struct *p)
{
        unsigned long interval = HZ;

        /* This task has no NUMA fault statistics yet */
        if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults_memory))
                return;

        /* Periodically retry migrating the task to the preferred node */
        interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
        p->numa_migrate_retry = jiffies + interval;

        /* Success if task is already running on preferred CPU */
        if (task_node(p) == p->numa_preferred_nid)
                return;

        /* Otherwise, try migrate to a CPU on the preferred node */
        task_numa_migrate(p);
}

/*
 * Find the nodes on which the workload is actively running. We do this by
 * tracking the nodes from which NUMA hinting faults are triggered. This can
 * be different from the set of nodes where the workload's memory is currently
 * located.
 *
 * The bitmask is used to make smarter decisions on when to do NUMA page
 * migrations, To prevent flip-flopping, and excessive page migrations, nodes
 * are added when they cause over 6/16 of the maximum number of faults, but
 * only removed when they drop below 3/16.
 */
static void update_numa_active_node_mask(struct numa_group *numa_group)
{
        unsigned long faults, max_faults = 0;
        int nid;

        for_each_online_node(nid) {
                faults = group_faults_cpu(numa_group, nid);
                if (faults > max_faults)
                        max_faults = faults;
        }

        for_each_online_node(nid) {
                faults = group_faults_cpu(numa_group, nid);
                if (!node_isset(nid, numa_group->active_nodes)) {
                        if (faults > max_faults * 6 / 16)
                                node_set(nid, numa_group->active_nodes);
                } else if (faults < max_faults * 3 / 16)
                        node_clear(nid, numa_group->active_nodes);
        }
}

/*
 * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
 * increments. The more local the fault statistics are, the higher the scan
 * period will be for the next scan window. If local/(local+remote) ratio is
 * below NUMA_PERIOD_THRESHOLD (where range of ratio is 1..NUMA_PERIOD_SLOTS)
 * the scan period will decrease. Aim for 70% local accesses.
 */
#define NUMA_PERIOD_SLOTS 10
#define NUMA_PERIOD_THRESHOLD 7

/*
 * Increase the scan period (slow down scanning) if the majority of
 * our memory is already on our local node, or if the majority of
 * the page accesses are shared with other processes.
 * Otherwise, decrease the scan period.
 */
static void update_task_scan_period(struct task_struct *p,
                        unsigned long shared, unsigned long private)
{
        unsigned int period_slot;
        int ratio;
        int diff;

        unsigned long remote = p->numa_faults_locality[0];
        unsigned long local = p->numa_faults_locality[1];

        /*
         * If there were no record hinting faults then either the task is
         * completely idle or all activity is areas that are not of interest
         * to automatic numa balancing. Scan slower
         */
        if (local + shared == 0) {
                p->numa_scan_period = min(p->numa_scan_period_max,
                        p->numa_scan_period << 1);

                p->mm->numa_next_scan = jiffies +
                        msecs_to_jiffies(p->numa_scan_period);

                return;
        }

        /*
         * Prepare to scale scan period relative to the current period.
         *       == NUMA_PERIOD_THRESHOLD scan period stays the same
         *       <  NUMA_PERIOD_THRESHOLD scan period decreases (scan faster)
         *       >= NUMA_PERIOD_THRESHOLD scan period increases (scan slower)
         */
        period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
        ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
        if (ratio >= NUMA_PERIOD_THRESHOLD) {
                int slot = ratio - NUMA_PERIOD_THRESHOLD;
                if (!slot)
                        slot = 1;
                diff = slot * period_slot;
        } else {
                diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;

                /*
                 * Scale scan rate increases based on sharing. There is an
                 * inverse relationship between the degree of sharing and
                 * the adjustment made to the scanning period. Broadly
                 * speaking the intent is that there is little point
                 * scanning faster if shared accesses dominate as it may
                 * simply bounce migrations uselessly
                 */
                ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared));
                diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
        }

        p->numa_scan_period = clamp(p->numa_scan_period + diff,
                        task_scan_min(p), task_scan_max(p));
        memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
}

/*
 * Get the fraction of time the task has been running since the last
 * NUMA placement cycle. The scheduler keeps similar statistics, but
 * decays those on a 32ms period, which is orders of magnitude off
 * from the dozens-of-seconds NUMA balancing period. Use the scheduler
 * stats only if the task is so new there are no NUMA statistics yet.
 */
static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
{
        u64 runtime, delta, now;
        /* Use the start of this time slice to avoid calculations. */
        now = p->se.exec_start;
        runtime = p->se.sum_exec_runtime;

        if (p->last_task_numa_placement) {
                delta = runtime - p->last_sum_exec_runtime;
                *period = now - p->last_task_numa_placement;
        } else {
                delta = p->se.avg.runnable_avg_sum;
                *period = p->se.avg.runnable_avg_period;
        }

        p->last_sum_exec_runtime = runtime;
        p->last_task_numa_placement = now;

        return delta;
}

static void task_numa_placement(struct task_struct *p)
{
        int seq, nid, max_nid = -1, max_group_nid = -1;
        unsigned long max_faults = 0, max_group_faults = 0;
        unsigned long fault_types[2] = { 0, 0 };
        unsigned long total_faults;
        u64 runtime, period;
        spinlock_t *group_lock = NULL;

        seq = ACCESS_ONCE(p->mm->numa_scan_seq);
        if (p->numa_scan_seq == seq)
                return;
        p->numa_scan_seq = seq;
        p->numa_scan_period_max = task_scan_max(p);

        total_faults = p->numa_faults_locality[0] +
                       p->numa_faults_locality[1];
        runtime = numa_get_avg_runtime(p, &period);

        /* If the task is part of a group prevent parallel updates to group stats */
        if (p->numa_group) {
                group_lock = &p->numa_group->lock;
                spin_lock_irq(group_lock);
        }

        /* Find the node with the highest number of faults */
        for_each_online_node(nid) {
                unsigned long faults = 0, group_faults = 0;
                int priv, i;

                for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
                        long diff, f_diff, f_weight;

                        i = task_faults_idx(nid, priv);

                        /* Decay existing window, copy faults since last scan */
                        diff = p->numa_faults_buffer_memory[i] - p->numa_faults_memory[i] / 2;
                        fault_types[priv] += p->numa_faults_buffer_memory[i];
                        p->numa_faults_buffer_memory[i] = 0;

                        /*
                         * Normalize the faults_from, so all tasks in a group
                         * count according to CPU use, instead of by the raw
                         * number of faults. Tasks with little runtime have
                         * little over-all impact on throughput, and thus their
                         * faults are less important.
                         */
                        f_weight = div64_u64(runtime << 16, period + 1);
                        f_weight = (f_weight * p->numa_faults_buffer_cpu[i]) /
                                   (total_faults + 1);
                        f_diff = f_weight - p->numa_faults_cpu[i] / 2;
                        p->numa_faults_buffer_cpu[i] = 0;

                        p->numa_faults_memory[i] += diff;
                        p->numa_faults_cpu[i] += f_diff;
                        faults += p->numa_faults_memory[i];
                        p->total_numa_faults += diff;
                        if (p->numa_group) {
                                /* safe because we can only change our own group */
                                p->numa_group->faults[i] += diff;
                                p->numa_group->faults_cpu[i] += f_diff;
                                p->numa_group->total_faults += diff;
                                group_faults += p->numa_group->faults[i];
                        }
                }

                if (faults > max_faults) {
                        max_faults = faults;
                        max_nid = nid;
                }

                if (group_faults > max_group_faults) {
                        max_group_faults = group_faults;
                        max_group_nid = nid;
                }
        }

        update_task_scan_period(p, fault_types[0], fault_types[1]);

        if (p->numa_group) {
                update_numa_active_node_mask(p->numa_group);
                spin_unlock_irq(group_lock);
                max_nid = max_group_nid;
        }

        if (max_faults) {
                /* Set the new preferred node */
                if (max_nid != p->numa_preferred_nid)
                        sched_setnuma(p, max_nid);

                if (task_node(p) != p->numa_preferred_nid)
                        numa_migrate_preferred(p);
        }
}

static inline int get_numa_group(struct numa_group *grp)
{
        return atomic_inc_not_zero(&grp->refcount);
}

static inline void put_numa_group(struct numa_group *grp)
{
        if (atomic_dec_and_test(&grp->refcount))
                kfree_rcu(grp, rcu);
}

static void task_numa_group(struct task_struct *p, int cpupid, int flags,
                        int *priv)
{
        struct numa_group *grp, *my_grp;
        struct task_struct *tsk;
        bool join = false;
        int cpu = cpupid_to_cpu(cpupid);
        int i;

        if (unlikely(!p->numa_group)) {
                unsigned int size = sizeof(struct numa_group) +
                                    4*nr_node_ids*sizeof(unsigned long);

                grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
                if (!grp)
                        return;

                atomic_set(&grp->refcount, 1);
                spin_lock_init(&grp->lock);
                INIT_LIST_HEAD(&grp->task_list);
                grp->gid = p->pid;
                /* Second half of the array tracks nids where faults happen */
                grp->faults_cpu = grp->faults + NR_NUMA_HINT_FAULT_TYPES *
                                                nr_node_ids;

                node_set(task_node(current), grp->active_nodes);

                for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
                        grp->faults[i] = p->numa_faults_memory[i];

                grp->total_faults = p->total_numa_faults;

                list_add(&p->numa_entry, &grp->task_list);
                grp->nr_tasks++;
                rcu_assign_pointer(p->numa_group, grp);
        }

        rcu_read_lock();
        tsk = ACCESS_ONCE(cpu_rq(cpu)->curr);

        if (!cpupid_match_pid(tsk, cpupid))
                goto no_join;

        grp = rcu_dereference(tsk->numa_group);
        if (!grp)
                goto no_join;

        my_grp = p->numa_group;
        if (grp == my_grp)
                goto no_join;

        /*
         * Only join the other group if its bigger; if we're the bigger group,
         * the other task will join us.
         */
        if (my_grp->nr_tasks > grp->nr_tasks)
                goto no_join;

        /*
         * Tie-break on the grp address.
         */
        if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)
                goto no_join;

        /* Always join threads in the same process. */
        if (tsk->mm == current->mm)
                join = true;

        /* Simple filter to avoid false positives due to PID collisions */
        if (flags & TNF_SHARED)
                join = true;

        /* Update priv based on whether false sharing was detected */
        *priv = !join;

        if (join && !get_numa_group(grp))
                goto no_join;

        rcu_read_unlock();

        if (!join)
                return;

        BUG_ON(irqs_disabled());
        double_lock_irq(&my_grp->lock, &grp->lock);

        for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
                my_grp->faults[i] -= p->numa_faults_memory[i];
                grp->faults[i] += p->numa_faults_memory[i];
        }
        my_grp->total_faults -= p->total_numa_faults;
        grp->total_faults += p->total_numa_faults;

        list_move(&p->numa_entry, &grp->task_list);
        my_grp->nr_tasks--;
        grp->nr_tasks++;

        spin_unlock(&my_grp->lock);
        spin_unlock_irq(&grp->lock);

        rcu_assign_pointer(p->numa_group, grp);

        put_numa_group(my_grp);
        return;

no_join:
        rcu_read_unlock();
        return;
}

void task_numa_free(struct task_struct *p)
{
        struct numa_group *grp = p->numa_group;
        void *numa_faults = p->numa_faults_memory;
        unsigned long flags;
        int i;

        if (grp) {
                spin_lock_irqsave(&grp->lock, flags);
                for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
                        grp->faults[i] -= p->numa_faults_memory[i];
                grp->total_faults -= p->total_numa_faults;

                list_del(&p->numa_entry);
                grp->nr_tasks--;
                spin_unlock_irqrestore(&grp->lock, flags);
                rcu_assign_pointer(p->numa_group, NULL);
                put_numa_group(grp);
        }

        p->numa_faults_memory = NULL;
        p->numa_faults_buffer_memory = NULL;
        p->numa_faults_cpu= NULL;
        p->numa_faults_buffer_cpu = NULL;
        kfree(numa_faults);
}

/*
 * Got a PROT_NONE fault for a page on @node.
 */
void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
{
        struct task_struct *p = current;
        bool migrated = flags & TNF_MIGRATED;
        int cpu_node = task_node(current);
        int local = !!(flags & TNF_FAULT_LOCAL);
        int priv;

        if (!numabalancing_enabled)
                return;

        /* for example, ksmd faulting in a user's mm */
        if (!p->mm)
                return;

        /* Do not worry about placement if exiting */
        if (p->state == TASK_DEAD)
                return;

        /* Allocate buffer to track faults on a per-node basis */
        if (unlikely(!p->numa_faults_memory)) {
                int size = sizeof(*p->numa_faults_memory) *
                           NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids;

                p->numa_faults_memory = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
                if (!p->numa_faults_memory)
                        return;

                BUG_ON(p->numa_faults_buffer_memory);
                /*
                 * The averaged statistics, shared & private, memory & cpu,
                 * occupy the first half of the array. The second half of the
                 * array is for current counters, which are averaged into the
                 * first set by task_numa_placement.
                 */
                p->numa_faults_cpu = p->numa_faults_memory + (2 * nr_node_ids);
                p->numa_faults_buffer_memory = p->numa_faults_memory + (4 * nr_node_ids);
                p->numa_faults_buffer_cpu = p->numa_faults_memory + (6 * nr_node_ids);
                p->total_numa_faults = 0;
                memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
        }

        /*
         * First accesses are treated as private, otherwise consider accesses
         * to be private if the accessing pid has not changed
         */
        if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
                priv = 1;
        } else {
                priv = cpupid_match_pid(p, last_cpupid);
                if (!priv && !(flags & TNF_NO_GROUP))
                        task_numa_group(p, last_cpupid, flags, &priv);
        }

        /*
         * If a workload spans multiple NUMA nodes, a shared fault that
         * occurs wholly within the set of nodes that the workload is
         * actively using should be counted as local. This allows the
         * scan rate to slow down when a workload has settled down.
         */
        if (!priv && !local && p->numa_group &&
                        node_isset(cpu_node, p->numa_group->active_nodes) &&
                        node_isset(mem_node, p->numa_group->active_nodes))
                local = 1;

        task_numa_placement(p);

        /*
         * Retry task to preferred node migration periodically, in case it
         * case it previously failed, or the scheduler moved us.
         */
        if (time_after(jiffies, p->numa_migrate_retry))
                numa_migrate_preferred(p);

        if (migrated)
                p->numa_pages_migrated += pages;

        p->numa_faults_buffer_memory[task_faults_idx(mem_node, priv)] += pages;
        p->numa_faults_buffer_cpu[task_faults_idx(cpu_node, priv)] += pages;
        p->numa_faults_locality[local] += pages;
}

static void reset_ptenuma_scan(struct task_struct *p)
{
        ACCESS_ONCE(p->mm->numa_scan_seq)++;
        p->mm->numa_scan_offset = 0;
}

/*
 * The expensive part of numa migration is done from task_work context.
 * Triggered from task_tick_numa().
 */
void task_numa_work(struct callback_head *work)
{
        unsigned long migrate, next_scan, now = jiffies;
        struct task_struct *p = current;
        struct mm_struct *mm = p->mm;
        struct vm_area_struct *vma;
        unsigned long start, end;
        unsigned long nr_pte_updates = 0;
        long pages;

        WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));

        work->next = work; /* protect against double add */
        /*
         * Who cares about NUMA placement when they're dying.
         *
         * NOTE: make sure not to dereference p->mm before this check,
         * exit_task_work() happens _after_ exit_mm() so we could be called
         * without p->mm even though we still had it when we enqueued this
         * work.
         */
        if (p->flags & PF_EXITING)
                return;

        if (!mm->numa_next_scan) {
                mm->numa_next_scan = now +
                        msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
        }

        /*
         * Enforce maximal scan/migration frequency..
         */
        migrate = mm->numa_next_scan;
        if (time_before(now, migrate))
                return;

        if (p->numa_scan_period == 0) {
                p->numa_scan_period_max = task_scan_max(p);
                p->numa_scan_period = task_scan_min(p);
        }

        next_scan = now + msecs_to_jiffies(p->numa_scan_period);
        if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
                return;

        /*
         * Delay this task enough that another task of this mm will likely win
         * the next time around.
         */
        p->node_stamp += 2 * TICK_NSEC;

        start = mm->numa_scan_offset;
        pages = sysctl_numa_balancing_scan_size;
        pages <<= 20 - PAGE_SHIFT; /* MB in pages */
        if (!pages)
                return;

        down_read(&mm->mmap_sem);
        vma = find_vma(mm, start);
        if (!vma) {
                reset_ptenuma_scan(p);
                start = 0;
                vma = mm->mmap;
        }
        for (; vma; vma = vma->vm_next) {
                if (!vma_migratable(vma) || !vma_policy_mof(p, vma))
                        continue;

                /*
                 * Shared library pages mapped by multiple processes are not
                 * migrated as it is expected they are cache replicated. Avoid
                 * hinting faults in read-only file-backed mappings or the vdso
                 * as migrating the pages will be of marginal benefit.
                 */
                if (!vma->vm_mm ||
                    (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ)))
                        continue;

                /*
                 * Skip inaccessible VMAs to avoid any confusion between
                 * PROT_NONE and NUMA hinting ptes
                 */
                if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        continue;

                do {
                        start = max(start, vma->vm_start);
                        end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
                        end = min(end, vma->vm_end);
                        nr_pte_updates += change_prot_numa(vma, start, end);

                        /*
                         * Scan sysctl_numa_balancing_scan_size but ensure that
                         * at least one PTE is updated so that unused virtual
                         * address space is quickly skipped.
                         */
                        if (nr_pte_updates)
                                pages -= (end - start) >> PAGE_SHIFT;

                        start = end;
                        if (pages <= 0)
                                goto out;

                        cond_resched();
                } while (end != vma->vm_end);
        }

out:
        /*
         * It is possible to reach the end of the VMA list but the last few
         * VMAs are not guaranteed to the vma_migratable. If they are not, we
         * would find the !migratable VMA on the next scan but not reset the
         * scanner to the start so check it now.
         */
        if (vma)
                mm->numa_scan_offset = start;
        else
                reset_ptenuma_scan(p);
        up_read(&mm->mmap_sem);
}

/*
 * Drive the periodic memory faults..
 */
void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
        struct callback_head *work = &curr->numa_work;
        u64 period, now;

        /*
         * We don't care about NUMA placement if we don't have memory.
         */
        if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work)
                return;

        /*
         * Using runtime rather than walltime has the dual advantage that
         * we (mostly) drive the selection from busy threads and that the
         * task needs to have done some actual work before we bother with
         * NUMA placement.
         */
        now = curr->se.sum_exec_runtime;
        period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;

        if (now - curr->node_stamp > period) {
                if (!curr->node_stamp)
                        curr->numa_scan_period = task_scan_min(curr);
                curr->node_stamp += period;

                if (!time_before(jiffies, curr->mm->numa_next_scan)) {
                        init_task_work(work, task_numa_work); /* TODO: move this into sched_fork() */
                        task_work_add(curr, work, true);
                }
        }
}
#else
static void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
}

static inline void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
}

static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
}
#endif /* CONFIG_NUMA_BALANCING */

static void
account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        update_load_add(&cfs_rq->load, se->load.weight);
        if (!parent_entity(se))
                update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
        if (entity_is_task(se)) {
                struct rq *rq = rq_of(cfs_rq);

                account_numa_enqueue(rq, task_of(se));
                list_add(&se->group_node, &rq->cfs_tasks);
        }
#endif
        cfs_rq->nr_running++;
}

static void
account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        update_load_sub(&cfs_rq->load, se->load.weight);
        if (!parent_entity(se))
                update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
        if (entity_is_task(se)) {
                account_numa_dequeue(rq_of(cfs_rq), task_of(se));
                list_del_init(&se->group_node);
        }
        cfs_rq->nr_running--;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
# ifdef CONFIG_SMP
static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
{
        long tg_weight;

        /*
         * Use this CPU's actual weight instead of the last load_contribution
         * to gain a more accurate current total weight. See
         * update_cfs_rq_load_contribution().
         */
        tg_weight = atomic_long_read(&tg->load_avg);
        tg_weight -= cfs_rq->tg_load_contrib;
        tg_weight += cfs_rq->load.weight;

        return tg_weight;
}

static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
        long tg_weight, load, shares;

        tg_weight = calc_tg_weight(tg, cfs_rq);
        load = cfs_rq->load.weight;

        shares = (tg->shares * load);
        if (tg_weight)
                shares /= tg_weight;

        if (shares < MIN_SHARES)
                shares = MIN_SHARES;
        if (shares > tg->shares)
                shares = tg->shares;

        return shares;
}
# else /* CONFIG_SMP */
static inline long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
        return tg->shares;
}
# endif /* CONFIG_SMP */
static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
                            unsigned long weight)
{
        if (se->on_rq) {
                /* commit outstanding execution time */
                if (cfs_rq->curr == se)
                        update_curr(cfs_rq);
                account_entity_dequeue(cfs_rq, se);
        }

        update_load_set(&se->load, weight);

        if (se->on_rq)
                account_entity_enqueue(cfs_rq, se);
}

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

static void update_cfs_shares(struct cfs_rq *cfs_rq)
{
        struct task_group *tg;
        struct sched_entity *se;
        long shares;

        tg = cfs_rq->tg;
        se = tg->se[cpu_of(rq_of(cfs_rq))];
        if (!se || throttled_hierarchy(cfs_rq))
                return;
#ifndef CONFIG_SMP
        if (likely(se->load.weight == tg->shares))
                return;
#endif
        shares = calc_cfs_shares(cfs_rq, tg);

        reweight_entity(cfs_rq_of(se), se, shares);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
{
}
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_SMP
/*
 * We choose a half-life close to 1 scheduling period.
 * Note: The tables below are dependent on this value.
 */
#define LOAD_AVG_PERIOD 32
#define LOAD_AVG_MAX 47742 /* maximum possible load avg */
#define LOAD_AVG_MAX_N 345 /* number of full periods to produce LOAD_MAX_AVG */

/* Precomputed fixed inverse multiplies for multiplication by y^n */
static const u32 runnable_avg_yN_inv[] = {
        0xffffffff, 0xfa83b2da, 0xf5257d14, 0xefe4b99a, 0xeac0c6e6, 0xe5b906e6,
        0xe0ccdeeb, 0xdbfbb796, 0xd744fcc9, 0xd2a81d91, 0xce248c14, 0xc9b9bd85,
        0xc5672a10, 0xc12c4cc9, 0xbd08a39e, 0xb8fbaf46, 0xb504f333, 0xb123f581,
        0xad583ee9, 0xa9a15ab4, 0xa5fed6a9, 0xa2704302, 0x9ef5325f, 0x9b8d39b9,
        0x9837f050, 0x94f4efa8, 0x91c3d373, 0x8ea4398a, 0x8b95c1e3, 0x88980e80,
        0x85aac367, 0x82cd8698,
};

/*
 * Precomputed \Sum y^k { 1<=k<=n }.  These are floor(true_value) to prevent
 * over-estimates when re-combining.
 */
static const u32 runnable_avg_yN_sum[] = {
            0, 1002, 1982, 2941, 3880, 4798, 5697, 6576, 7437, 8279, 9103,
         9909,10698,11470,12226,12966,13690,14398,15091,15769,16433,17082,
        17718,18340,18949,19545,20128,20698,21256,21802,22336,22859,23371,
};

/*
 * Approximate:
 *   val * y^n,    where y^32 ~= 0.5 (~1 scheduling period)
 */
static __always_inline u64 decay_load(u64 val, u64 n)
{
        unsigned int local_n;

        if (!n)
                return val;
        else if (unlikely(n > LOAD_AVG_PERIOD * 63))
                return 0;

        /* after bounds checking we can collapse to 32-bit */
        local_n = n;

        /*
         * As y^PERIOD = 1/2, we can combine
         *    y^n = 1/2^(n/PERIOD) * k^(n%PERIOD)
         * With a look-up table which covers k^n (n<PERIOD)
         *
         * To achieve constant time decay_load.
         */
        if (unlikely(local_n >= LOAD_AVG_PERIOD)) {
                val >>= local_n / LOAD_AVG_PERIOD;
                local_n %= LOAD_AVG_PERIOD;
        }

        val *= runnable_avg_yN_inv[local_n];
        /* We don't use SRR here since we always want to round down. */
        return val >> 32;
}

/*
 * For updates fully spanning n periods, the contribution to runnable
 * average will be: \Sum 1024*y^n
 *
 * We can compute this reasonably efficiently by combining:
 *   y^PERIOD = 1/2 with precomputed \Sum 1024*y^n {for  n <PERIOD}
 */
static u32 __compute_runnable_contrib(u64 n)
{
        u32 contrib = 0;

        if (likely(n <= LOAD_AVG_PERIOD))
                return runnable_avg_yN_sum[n];
        else if (unlikely(n >= LOAD_AVG_MAX_N))
                return LOAD_AVG_MAX;

        /* Compute \Sum k^n combining precomputed values for k^i, \Sum k^j */
        do {
                contrib /= 2; /* y^LOAD_AVG_PERIOD = 1/2 */
                contrib += runnable_avg_yN_sum[LOAD_AVG_PERIOD];

                n -= LOAD_AVG_PERIOD;
        } while (n > LOAD_AVG_PERIOD);

        contrib = decay_load(contrib, n);
        return contrib + runnable_avg_yN_sum[n];
}

/*
 * We can represent the historical contribution to runnable average as the
 * coefficients of a geometric series.  To do this we sub-divide our runnable
 * history into segments of approximately 1ms (1024us); label the segment that
 * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g.
 *
 * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ...
 *      p0            p1           p2
 *     (now)       (~1ms ago)  (~2ms ago)
 *
 * Let u_i denote the fraction of p_i that the entity was runnable.
 *
 * We then designate the fractions u_i as our co-efficients, yielding the
 * following representation of historical load:
 *   u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ...
 *
 * We choose y based on the with of a reasonably scheduling period, fixing:
 *   y^32 = 0.5
 *
 * This means that the contribution to load ~32ms ago (u_32) will be weighted
 * approximately half as much as the contribution to load within the last ms
 * (u_0).
 *
 * When a period "rolls over" and we have new u_0`, multiplying the previous
 * sum again by y is sufficient to update:
 *   load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... )
 *            = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}]
 */
static __always_inline int __update_entity_runnable_avg(u64 now,
                                                        struct sched_avg *sa,
                                                        int runnable)
{
        u64 delta, periods;
        u32 runnable_contrib;
        int delta_w, decayed = 0;

        delta = now - sa->last_runnable_update;
        /*
         * This should only happen when time goes backwards, which it
         * unfortunately does during sched clock init when we swap over to TSC.
         */
        if ((s64)delta < 0) {
                sa->last_runnable_update = now;
                return 0;
        }

        /*
         * Use 1024ns as the unit of measurement since it's a reasonable
         * approximation of 1us and fast to compute.
         */
        delta >>= 10;
        if (!delta)
                return 0;
        sa->last_runnable_update = now;

        /* delta_w is the amount already accumulated against our next period */
        delta_w = sa->runnable_avg_period % 1024;
        if (delta + delta_w >= 1024) {
                /* period roll-over */
                decayed = 1;

                /*
                 * Now that we know we're crossing a period boundary, figure
                 * out how much from delta we need to complete the current
                 * period and accrue it.
                 */
                delta_w = 1024 - delta_w;
                if (runnable)
                        sa->runnable_avg_sum += delta_w;
                sa->runnable_avg_period += delta_w;

                delta -= delta_w;

                /* Figure out how many additional periods this update spans */
                periods = delta / 1024;
                delta %= 1024;

                sa->runnable_avg_sum = decay_load(sa->runnable_avg_sum,
                                                  periods + 1);
                sa->runnable_avg_period = decay_load(sa->runnable_avg_period,
                                                     periods + 1);

                /* Efficiently calculate \sum (1..n_period) 1024*y^i */
                runnable_contrib = __compute_runnable_contrib(periods);
                if (runnable)
                        sa->runnable_avg_sum += runnable_contrib;
                sa->runnable_avg_period += runnable_contrib;
        }

        /* Remainder of delta accrued against u_0` */
        if (runnable)
                sa->runnable_avg_sum += delta;
        sa->runnable_avg_period += delta;

        return decayed;
}

/* Synchronize an entity's decay with its parenting cfs_rq.*/
static inline u64 __synchronize_entity_decay(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        u64 decays = atomic64_read(&cfs_rq->decay_counter);

        decays -= se->avg.decay_count;
        if (!decays)
                return 0;

        se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays);
        se->avg.decay_count = 0;

        return decays;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
                                                 int force_update)
{
        struct task_group *tg = cfs_rq->tg;
        long tg_contrib;

        tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;
        tg_contrib -= cfs_rq->tg_load_contrib;

        if (force_update || abs(tg_contrib) > cfs_rq->tg_load_contrib / 8) {
                atomic_long_add(tg_contrib, &tg->load_avg);
                cfs_rq->tg_load_contrib += tg_contrib;
        }
}

/*
 * Aggregate cfs_rq runnable averages into an equivalent task_group
 * representation for computing load contributions.
 */
static inline void __update_tg_runnable_avg(struct sched_avg *sa,
                                                  struct cfs_rq *cfs_rq)
{
        struct task_group *tg = cfs_rq->tg;
        long contrib;

        /* The fraction of a cpu used by this cfs_rq */
        contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
                          sa->runnable_avg_period + 1);
        contrib -= cfs_rq->tg_runnable_contrib;

        if (abs(contrib) > cfs_rq->tg_runnable_contrib / 64) {
                atomic_add(contrib, &tg->runnable_avg);
                cfs_rq->tg_runnable_contrib += contrib;
        }
}

static inline void __update_group_entity_contrib(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = group_cfs_rq(se);
        struct task_group *tg = cfs_rq->tg;
        int runnable_avg;

        u64 contrib;

        contrib = cfs_rq->tg_load_contrib * tg->shares;
        se->avg.load_avg_contrib = div_u64(contrib,
                                     atomic_long_read(&tg->load_avg) + 1);

        /*
         * For group entities we need to compute a correction term in the case
         * that they are consuming <1 cpu so that we would contribute the same
         * load as a task of equal weight.
         *
         * Explicitly co-ordinating this measurement would be expensive, but
         * fortunately the sum of each cpus contribution forms a usable
         * lower-bound on the true value.
         *
         * Consider the aggregate of 2 contributions.  Either they are disjoint
         * (and the sum represents true value) or they are disjoint and we are
         * understating by the aggregate of their overlap.
         *
         * Extending this to N cpus, for a given overlap, the maximum amount we
         * understand is then n_i(n_i+1)/2 * w_i where n_i is the number of
         * cpus that overlap for this interval and w_i is the interval width.
         *
         * On a small machine; the first term is well-bounded which bounds the
         * total error since w_i is a subset of the period.  Whereas on a
         * larger machine, while this first term can be larger, if w_i is the
         * of consequential size guaranteed to see n_i*w_i quickly converge to
         * our upper bound of 1-cpu.
         */
        runnable_avg = atomic_read(&tg->runnable_avg);
        if (runnable_avg < NICE_0_LOAD) {
                se->avg.load_avg_contrib *= runnable_avg;
                se->avg.load_avg_contrib >>= NICE_0_SHIFT;
        }
}

static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
{
        __update_entity_runnable_avg(rq_clock_task(rq), &rq->avg, runnable);
        __update_tg_runnable_avg(&rq->avg, &rq->cfs);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
                                                 int force_update) {}
static inline void __update_tg_runnable_avg(struct sched_avg *sa,
                                                  struct cfs_rq *cfs_rq) {}
static inline void __update_group_entity_contrib(struct sched_entity *se) {}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
#endif /* CONFIG_FAIR_GROUP_SCHED */

static inline void __update_task_entity_contrib(struct sched_entity *se)
{
        u32 contrib;

        /* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
        contrib = se->avg.runnable_avg_sum * scale_load_down(se->load.weight);
        contrib /= (se->avg.runnable_avg_period + 1);
        se->avg.load_avg_contrib = scale_load(contrib);
}

/* Compute the current contribution to load_avg by se, return any delta */
static long __update_entity_load_avg_contrib(struct sched_entity *se)
{
        long old_contrib = se->avg.load_avg_contrib;

        if (entity_is_task(se)) {
                __update_task_entity_contrib(se);
        } else {
                __update_tg_runnable_avg(&se->avg, group_cfs_rq(se));
                __update_group_entity_contrib(se);
        }

        return se->avg.load_avg_contrib - old_contrib;
}

static inline void subtract_blocked_load_contrib(struct cfs_rq *cfs_rq,
                                                 long load_contrib)
{
        if (likely(load_contrib < cfs_rq->blocked_load_avg))
                cfs_rq->blocked_load_avg -= load_contrib;
        else
                cfs_rq->blocked_load_avg = 0;
}

static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);

/* Update a sched_entity's runnable average */
static inline void update_entity_load_avg(struct sched_entity *se,
                                          int update_cfs_rq)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        long contrib_delta;
        u64 now;

        /*
         * For a group entity we need to use their owned cfs_rq_clock_task() in
         * case they are the parent of a throttled hierarchy.
         */
        if (entity_is_task(se))
                now = cfs_rq_clock_task(cfs_rq);
        else
                now = cfs_rq_clock_task(group_cfs_rq(se));

        if (!__update_entity_runnable_avg(now, &se->avg, se->on_rq))
                return;

        contrib_delta = __update_entity_load_avg_contrib(se);

        if (!update_cfs_rq)
                return;

        if (se->on_rq)
                cfs_rq->runnable_load_avg += contrib_delta;
        else
                subtract_blocked_load_contrib(cfs_rq, -contrib_delta);
}

/*
 * Decay the load contributed by all blocked children and account this so that
 * their contribution may appropriately discounted when they wake up.
 */
static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update)
{
        u64 now = cfs_rq_clock_task(cfs_rq) >> 20;
        u64 decays;

        decays = now - cfs_rq->last_decay;
        if (!decays && !force_update)
                return;

        if (atomic_long_read(&cfs_rq->removed_load)) {
                unsigned long removed_load;
                removed_load = atomic_long_xchg(&cfs_rq->removed_load, 0);
                subtract_blocked_load_contrib(cfs_rq, removed_load);
        }

        if (decays) {
                cfs_rq->blocked_load_avg = decay_load(cfs_rq->blocked_load_avg,
                                                      decays);
                atomic64_add(decays, &cfs_rq->decay_counter);
                cfs_rq->last_decay = now;
        }

        __update_cfs_rq_tg_load_contrib(cfs_rq, force_update);
}

/* Add the load generated by se into cfs_rq's child load-average */
static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
                                                  struct sched_entity *se,
                                                  int wakeup)
{
        /*
         * We track migrations using entity decay_count <= 0, on a wake-up
         * migration we use a negative decay count to track the remote decays
         * accumulated while sleeping.
         *
         * Newly forked tasks are enqueued with se->avg.decay_count == 0, they
         * are seen by enqueue_entity_load_avg() as a migration with an already
         * constructed load_avg_contrib.
         */
        if (unlikely(se->avg.decay_count <= 0)) {
                se->avg.last_runnable_update = rq_clock_task(rq_of(cfs_rq));
                if (se->avg.decay_count) {
                        /*
                         * In a wake-up migration we have to approximate the
                         * time sleeping.  This is because we can't synchronize
                         * clock_task between the two cpus, and it is not
                         * guaranteed to be read-safe.  Instead, we can
                         * approximate this using our carried decays, which are
                         * explicitly atomically readable.
                         */
                        se->avg.last_runnable_update -= (-se->avg.decay_count)
                                                        << 20;
                        update_entity_load_avg(se, 0);
                        /* Indicate that we're now synchronized and on-rq */
                        se->avg.decay_count = 0;
                }
                wakeup = 0;
        } else {
                __synchronize_entity_decay(se);
        }

        /* migrated tasks did not contribute to our blocked load */
        if (wakeup) {
                subtract_blocked_load_contrib(cfs_rq, se->avg.load_avg_contrib);
                update_entity_load_avg(se, 0);
        }

        cfs_rq->runnable_load_avg += se->avg.load_avg_contrib;
        /* we force update consideration on load-balancer moves */
        update_cfs_rq_blocked_load(cfs_rq, !wakeup);
}

/*
 * Remove se's load from this cfs_rq child load-average, if the entity is
 * transitioning to a blocked state we track its projected decay using
 * blocked_load_avg.
 */
static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
                                                  struct sched_entity *se,
                                                  int sleep)
{
        update_entity_load_avg(se, 1);
        /* we force update consideration on load-balancer moves */
        update_cfs_rq_blocked_load(cfs_rq, !sleep);

        cfs_rq->runnable_load_avg -= se->avg.load_avg_contrib;
        if (sleep) {
                cfs_rq->blocked_load_avg += se->avg.load_avg_contrib;
                se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);
        } /* migrations, e.g. sleep=0 leave decay_count == 0 */
}

/*
 * Update the rq's load with the elapsed running time before entering
 * idle. if the last scheduled task is not a CFS task, idle_enter will
 * be the only way to update the runnable statistic.
 */
void idle_enter_fair(struct rq *this_rq)
{
        update_rq_runnable_avg(this_rq, 1);
}

/*
 * Update the rq's load with the elapsed idle time before a task is
 * scheduled. if the newly scheduled task is not a CFS task, idle_exit will
 * be the only way to update the runnable statistic.
 */
void idle_exit_fair(struct rq *this_rq)
{
        update_rq_runnable_avg(this_rq, 0);
}

static int idle_balance(struct rq *this_rq);

#else /* CONFIG_SMP */

static inline void update_entity_load_avg(struct sched_entity *se,
                                          int update_cfs_rq) {}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
                                           struct sched_entity *se,
                                           int wakeup) {}
static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
                                           struct sched_entity *se,
                                           int sleep) {}
static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
                                              int force_update) {}

static inline int idle_balance(struct rq *rq)
{
        return 0;
}

#endif /* CONFIG_SMP */

static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHEDSTATS
        struct task_struct *tsk = NULL;

        if (entity_is_task(se))
                tsk = task_of(se);

        if (se->statistics.sleep_start) {
                u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.sleep_start;

                if ((s64)delta < 0)
                        delta = 0;

                if (unlikely(delta > se->statistics.sleep_max))
                        se->statistics.sleep_max = delta;

                se->statistics.sleep_start = 0;
                se->statistics.sum_sleep_runtime += delta;

                if (tsk) {
                        account_scheduler_latency(tsk, delta >> 10, 1);
                        trace_sched_stat_sleep(tsk, delta);
                }
        }
        if (se->statistics.block_start) {
                u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.block_start;

                if ((s64)delta < 0)
                        delta = 0;

                if (unlikely(delta > se->statistics.block_max))
                        se->statistics.block_max = delta;

                se->statistics.block_start = 0;
                se->statistics.sum_sleep_runtime += delta;

                if (tsk) {
                        if (tsk->in_iowait) {
                                se->statistics.iowait_sum += delta;
                                se->statistics.iowait_count++;
                                trace_sched_stat_iowait(tsk, delta);
                        }

                        trace_sched_stat_blocked(tsk, delta);

                        /*
                         * Blocking time is in units of nanosecs, so shift by
                         * 20 to get a milliseconds-range estimation of the
                         * amount of time that the task spent sleeping:
                         */
                        if (unlikely(prof_on == SLEEP_PROFILING)) {
                                profile_hits(SLEEP_PROFILING,
                                                (void *)get_wchan(tsk),
                                                delta >> 20);
                        }
                        account_scheduler_latency(tsk, delta >> 10, 0);
                }
        }
#endif
}

static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
        s64 d = se->vruntime - cfs_rq->min_vruntime;

        if (d < 0)
                d = -d;

        if (d > 3*sysctl_sched_latency)
                schedstat_inc(cfs_rq, nr_spread_over);
#endif
}

static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
        u64 vruntime = cfs_rq->min_vruntime;

        /*
         * The 'current' period is already promised to the current tasks,
         * however the extra weight of the new task will slow them down a
         * little, place the new task so that it fits in the slot that
         * stays open at the end.
         */
        if (initial && sched_feat(START_DEBIT))
                vruntime += sched_vslice(cfs_rq, se);

        /* sleeps up to a single latency don't count. */
        if (!initial) {
                unsigned long thresh = sysctl_sched_latency;

                /*
                 * Halve their sleep time's effect, to allow
                 * for a gentler effect of sleepers:
                 */
                if (sched_feat(GENTLE_FAIR_SLEEPERS))
                        thresh >>= 1;

                vruntime -= thresh;
        }

        /* ensure we never gain time by being placed backwards. */
        se->vruntime = max_vruntime(se->vruntime, vruntime);
}

static void check_enqueue_throttle(struct cfs_rq *cfs_rq);

static void
enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        /*
         * Update the normalized vruntime before updating min_vruntime
         * through calling update_curr().
         */
        if (!(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_WAKING))
                se->vruntime += cfs_rq->min_vruntime;

        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);
        enqueue_entity_load_avg(cfs_rq, se, flags & ENQUEUE_WAKEUP);
        account_entity_enqueue(cfs_rq, se);
        update_cfs_shares(cfs_rq);

        if (flags & ENQUEUE_WAKEUP) {
                place_entity(cfs_rq, se, 0);
                enqueue_sleeper(cfs_rq, se);
        }

        update_stats_enqueue(cfs_rq, se);
        check_spread(cfs_rq, se);
        if (se != cfs_rq->curr)
                __enqueue_entity(cfs_rq, se);
        se->on_rq = 1;

        if (cfs_rq->nr_running == 1) {
                list_add_leaf_cfs_rq(cfs_rq);
                check_enqueue_throttle(cfs_rq);
        }
}

static void __clear_buddies_last(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->last != se)
                        break;

                cfs_rq->last = NULL;
        }
}

static void __clear_buddies_next(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->next != se)
                        break;

                cfs_rq->next = NULL;
        }
}

static void __clear_buddies_skip(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->skip != se)
                        break;

                cfs_rq->skip = NULL;
        }
}

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (cfs_rq->last == se)
                __clear_buddies_last(se);

        if (cfs_rq->next == se)
                __clear_buddies_next(se);

        if (cfs_rq->skip == se)
                __clear_buddies_skip(se);
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);

static void
dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);
        dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);

        update_stats_dequeue(cfs_rq, se);
        if (flags & DEQUEUE_SLEEP) {
#ifdef CONFIG_SCHEDSTATS
                if (entity_is_task(se)) {
                        struct task_struct *tsk = task_of(se);

                        if (tsk->state & TASK_INTERRUPTIBLE)
                                se->statistics.sleep_start = rq_clock(rq_of(cfs_rq));
                        if (tsk->state & TASK_UNINTERRUPTIBLE)
                                se->statistics.block_start = rq_clock(rq_of(cfs_rq));
                }
#endif
        }

        clear_buddies(cfs_rq, se);

        if (se != cfs_rq->curr)
                __dequeue_entity(cfs_rq, se);
        se->on_rq = 0;
        account_entity_dequeue(cfs_rq, se);

        /*
         * Normalize the entity after updating the min_vruntime because the
         * update can refer to the ->curr item and we need to reflect this
         * movement in our normalized position.
         */
        if (!(flags & DEQUEUE_SLEEP))
                se->vruntime -= cfs_rq->min_vruntime;

        /* return excess runtime on last dequeue */
        return_cfs_rq_runtime(cfs_rq);

        update_min_vruntime(cfs_rq);
        update_cfs_shares(cfs_rq);
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void
check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
        unsigned long ideal_runtime, delta_exec;
        struct sched_entity *se;
        s64 delta;

        ideal_runtime = sched_slice(cfs_rq, curr);
        delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
        if (delta_exec > ideal_runtime) {
                resched_task(rq_of(cfs_rq)->curr);
                /*
                 * The current task ran long enough, ensure it doesn't get
                 * re-elected due to buddy favours.
                 */
                clear_buddies(cfs_rq, curr);
                return;
        }

        /*
         * Ensure that a task that missed wakeup preemption by a
         * narrow margin doesn't have to wait for a full slice.
         * This also mitigates buddy induced latencies under load.
         */
        if (delta_exec < sysctl_sched_min_granularity)
                return;

        se = __pick_first_entity(cfs_rq);
        delta = curr->vruntime - se->vruntime;

        if (delta < 0)
                return;

        if (delta > ideal_runtime)
                resched_task(rq_of(cfs_rq)->curr);
}

static void
set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /* 'current' is not kept within the tree. */
        if (se->on_rq) {
                /*
                 * Any task has to be enqueued before it get to execute on
                 * a CPU. So account for the time it spent waiting on the
                 * runqueue.
                 */
                update_stats_wait_end(cfs_rq, se);
                __dequeue_entity(cfs_rq, se);
        }

        update_stats_curr_start(cfs_rq, se);
        cfs_rq->curr = se;
#ifdef CONFIG_SCHEDSTATS
        /*
         * Track our maximum slice length, if the CPU's load is at
         * least twice that of our own weight (i.e. dont track it
         * when there are only lesser-weight tasks around):
         */
        if (rq_of(cfs_rq)->load.weight >= 2*se->load.weight) {
                se->statistics.slice_max = max(se->statistics.slice_max,
                        se->sum_exec_runtime - se->prev_sum_exec_runtime);
        }
#endif
        se->prev_sum_exec_runtime = se->sum_exec_runtime;
}

static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);

/*
 * Pick the next process, keeping these things in mind, in this order:
 * 1) keep things fair between processes/task groups
 * 2) pick the "next" process, since someone really wants that to run
 * 3) pick the "last" process, for cache locality
 * 4) do not run the "skip" process, if something else is available
 */
static struct sched_entity *
pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
        struct sched_entity *left = __pick_first_entity(cfs_rq);
        struct sched_entity *se;

        /*
         * If curr is set we have to see if its left of the leftmost entity
         * still in the tree, provided there was anything in the tree at all.
         */
        if (!left || (curr && entity_before(curr, left)))
                left = curr;

        se = left; /* ideally we run the leftmost entity */

        /*
         * Avoid running the skip buddy, if running something else can
         * be done without getting too unfair.
         */
        if (cfs_rq->skip == se) {
                struct sched_entity *second;

                if (se == curr) {
                        second = __pick_first_entity(cfs_rq);
                } else {
                        second = __pick_next_entity(se);
                        if (!second || (curr && entity_before(curr, second)))
                                second = curr;
                }

                if (second && wakeup_preempt_entity(second, left) < 1)
                        se = second;
        }

        /*
         * Prefer last buddy, try to return the CPU to a preempted task.
         */
        if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
                se = cfs_rq->last;

        /*
         * Someone really wants this to run. If it's not unfair, run it.
         */
        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
                se = cfs_rq->next;

        clear_buddies(cfs_rq, se);

        return se;
}

static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);

static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
{
        /*
         * If still on the runqueue then deactivate_task()
         * was not called and update_curr() has to be done:
         */
        if (prev->on_rq)
                update_curr(cfs_rq);

        /* throttle cfs_rqs exceeding runtime */
        check_cfs_rq_runtime(cfs_rq);

        check_spread(cfs_rq, prev);
        if (prev->on_rq) {
                update_stats_wait_start(cfs_rq, prev);
                /* Put 'current' back into the tree. */
                __enqueue_entity(cfs_rq, prev);
                /* in !on_rq case, update occurred at dequeue */
                update_entity_load_avg(prev, 1);
        }
        cfs_rq->curr = NULL;
}

static void
entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);

        /*
         * Ensure that runnable average is periodically updated.
         */
        update_entity_load_avg(curr, 1);
        update_cfs_rq_blocked_load(cfs_rq, 1);
        update_cfs_shares(cfs_rq);

#ifdef CONFIG_SCHED_HRTICK
        /*
         * queued ticks are scheduled to match the slice, so don't bother
         * validating it and just reschedule.
         */
        if (queued) {
                resched_task(rq_of(cfs_rq)->curr);
                return;
        }
        /*
         * don't let the period tick interfere with the hrtick preemption
         */
        if (!sched_feat(DOUBLE_TICK) &&
                        hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
                return;
#endif

        if (cfs_rq->nr_running > 1)
                check_preempt_tick(cfs_rq, curr);
}


/**************************************************
 * CFS bandwidth control machinery
 */

#ifdef CONFIG_CFS_BANDWIDTH

#ifdef HAVE_JUMP_LABEL
static struct static_key __cfs_bandwidth_used;

static inline bool cfs_bandwidth_used(void)
{
        return static_key_false(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_inc(void)
{
        static_key_slow_inc(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_dec(void)
{
        static_key_slow_dec(&__cfs_bandwidth_used);
}
#else /* HAVE_JUMP_LABEL */
static bool cfs_bandwidth_used(void)
{
        return true;
}

void cfs_bandwidth_usage_inc(void) {}
void cfs_bandwidth_usage_dec(void) {}
#endif /* HAVE_JUMP_LABEL */

/*
 * default period for cfs group bandwidth.
 * default: 0.1s, units: nanoseconds
 */
static inline u64 default_cfs_period(void)
{
        return 100000000ULL;
}

static inline u64 sched_cfs_bandwidth_slice(void)
{
        return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
}

/*
 * Replenish runtime according to assigned quota and update expiration time.
 * We use sched_clock_cpu directly instead of rq->clock to avoid adding
 * additional synchronization around rq->lock.
 *
 * requires cfs_b->lock
 */
void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
{
        u64 now;

        if (cfs_b->quota == RUNTIME_INF)
                return;

        now = sched_clock_cpu(smp_processor_id());
        cfs_b->runtime = cfs_b->quota;
        cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
}

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
        return &tg->cfs_bandwidth;
}

/* rq->task_clock normalized against any time this cfs_rq has spent throttled */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
        if (unlikely(cfs_rq->throttle_count))
                return cfs_rq->throttled_clock_task;

        return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
}

/* returns 0 on failure to allocate runtime */
static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct task_group *tg = cfs_rq->tg;
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
        u64 amount = 0, min_amount, expires;

        /* note: this is a positive sum as runtime_remaining <= 0 */
        min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;

        raw_spin_lock(&cfs_b->lock);
        if (cfs_b->quota == RUNTIME_INF)
                amount = min_amount;
        else {
                /*
                 * If the bandwidth pool has become inactive, then at least one
                 * period must have elapsed since the last consumption.
                 * Refresh the global state and ensure bandwidth timer becomes
                 * active.
                 */
                if (!cfs_b->timer_active) {
                        __refill_cfs_bandwidth_runtime(cfs_b);
                        __start_cfs_bandwidth(cfs_b, false);
                }

                if (cfs_b->runtime > 0) {
                        amount = min(cfs_b->runtime, min_amount);
                        cfs_b->runtime -= amount;
                        cfs_b->idle = 0;
                }
        }
        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);

        cfs_rq->runtime_remaining += amount;
        /*
         * we may have advanced our local expiration to account for allowed
         * spread between our sched_clock and the one on which runtime was
         * issued.
         */
        if ((s64)(expires - cfs_rq->runtime_expires) > 0)
                cfs_rq->runtime_expires = expires;

        return cfs_rq->runtime_remaining > 0;
}

/*
 * Note: This depends on the synchronization provided by sched_clock and the
 * fact that rq->clock snapshots this value.
 */
static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);

        /* if the deadline is ahead of our clock, nothing to do */
        if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0))
                return;

        if (cfs_rq->runtime_remaining < 0)
                return;

        /*
         * If the local deadline has passed we have to consider the
         * possibility that our sched_clock is 'fast' and the global deadline
         * has not truly expired.
         *
         * Fortunately we can check determine whether this the case by checking
         * whether the global deadline has advanced. It is valid to compare
         * cfs_b->runtime_expires without any locks since we only care about
         * exact equality, so a partial write will still work.
         */

        if (cfs_rq->runtime_expires != cfs_b->runtime_expires) {
                /* extend local deadline, drift is bounded above by 2 ticks */
                cfs_rq->runtime_expires += TICK_NSEC;
        } else {
                /* global deadline is ahead, expiration has passed */
                cfs_rq->runtime_remaining = 0;
        }
}

static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
        /* dock delta_exec before expiring quota (as it could span periods) */
        cfs_rq->runtime_remaining -= delta_exec;
        expire_cfs_rq_runtime(cfs_rq);

        if (likely(cfs_rq->runtime_remaining > 0))
                return;

        /*
         * if we're unable to extend our runtime we resched so that the active
         * hierarchy can be throttled
         */
        if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
                resched_task(rq_of(cfs_rq)->curr);
}

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
        if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
                return;

        __account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
        return cfs_bandwidth_used() && cfs_rq->throttled;
}

/* check whether cfs_rq, or any parent, is throttled */
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
        return cfs_bandwidth_used() && cfs_rq->throttle_count;
}

/*
 * Ensure that neither of the group entities corresponding to src_cpu or
 * dest_cpu are members of a throttled hierarchy when performing group
 * load-balance operations.
 */
static inline int throttled_lb_pair(struct task_group *tg,
                                    int src_cpu, int dest_cpu)
{
        struct cfs_rq *src_cfs_rq, *dest_cfs_rq;

        src_cfs_rq = tg->cfs_rq[src_cpu];
        dest_cfs_rq = tg->cfs_rq[dest_cpu];

        return throttled_hierarchy(src_cfs_rq) ||
               throttled_hierarchy(dest_cfs_rq);
}

/* updated child weight may affect parent so we have to do this bottom up */
static int tg_unthrottle_up(struct task_group *tg, void *data)
{
        struct rq *rq = data;
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

        cfs_rq->throttle_count--;
#ifdef CONFIG_SMP
        if (!cfs_rq->throttle_count) {
                /* adjust cfs_rq_clock_task() */
                cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
                                             cfs_rq->throttled_clock_task;
        }
#endif

        return 0;
}

static int tg_throttle_down(struct task_group *tg, void *data)
{
        struct rq *rq = data;
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

        /* group is entering throttled state, stop time */
        if (!cfs_rq->throttle_count)
                cfs_rq->throttled_clock_task = rq_clock_task(rq);
        cfs_rq->throttle_count++;

        return 0;
}

static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        struct sched_entity *se;
        long task_delta, dequeue = 1;

        se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];

        /* freeze hierarchy runnable averages while throttled */
        rcu_read_lock();
        walk_tg_tree_from(cfs_rq->tg, tg_throttle_down, tg_nop, (void *)rq);
        rcu_read_unlock();

        task_delta = cfs_rq->h_nr_running;
        for_each_sched_entity(se) {
                struct cfs_rq *qcfs_rq = cfs_rq_of(se);
                /* throttled entity or throttle-on-deactivate */
                if (!se->on_rq)
                        break;

                if (dequeue)
                        dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
                qcfs_rq->h_nr_running -= task_delta;

                if (qcfs_rq->load.weight)
                        dequeue = 0;
        }

        if (!se)
                sub_nr_running(rq, task_delta);

        cfs_rq->throttled = 1;
        cfs_rq->throttled_clock = rq_clock(rq);
        raw_spin_lock(&cfs_b->lock);
        /*
         * Add to the _head_ of the list, so that an already-started
         * distribute_cfs_runtime will not see us
         */
        list_add_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
        if (!cfs_b->timer_active)
                __start_cfs_bandwidth(cfs_b, false);
        raw_spin_unlock(&cfs_b->lock);
}

void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        struct sched_entity *se;
        int enqueue = 1;
        long task_delta;

        se = cfs_rq->tg->se[cpu_of(rq)];

        cfs_rq->throttled = 0;

        update_rq_clock(rq);

        raw_spin_lock(&cfs_b->lock);
        cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
        list_del_rcu(&cfs_rq->throttled_list);
        raw_spin_unlock(&cfs_b->lock);

        /* update hierarchical throttle state */
        walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);

        if (!cfs_rq->load.weight)
                return;

        task_delta = cfs_rq->h_nr_running;
        for_each_sched_entity(se) {
                if (se->on_rq)
                        enqueue = 0;

                cfs_rq = cfs_rq_of(se);
                if (enqueue)
                        enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
                cfs_rq->h_nr_running += task_delta;

                if (cfs_rq_throttled(cfs_rq))
                        break;
        }

        if (!se)
                add_nr_running(rq, task_delta);

        /* determine whether we need to wake up potentially idle cpu */
        if (rq->curr == rq->idle && rq->cfs.nr_running)
                resched_task(rq->curr);
}

static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
                u64 remaining, u64 expires)
{
        struct cfs_rq *cfs_rq;
        u64 runtime;
        u64 starting_runtime = remaining;

        rcu_read_lock();
        list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
                                throttled_list) {
                struct rq *rq = rq_of(cfs_rq);

                raw_spin_lock(&rq->lock);
                if (!cfs_rq_throttled(cfs_rq))
                        goto next;

                runtime = -cfs_rq->runtime_remaining + 1;
                if (runtime > remaining)
                        runtime = remaining;
                remaining -= runtime;

                cfs_rq->runtime_remaining += runtime;
                cfs_rq->runtime_expires = expires;

                /* we check whether we're throttled above */
                if (cfs_rq->runtime_remaining > 0)
                        unthrottle_cfs_rq(cfs_rq);

next:
                raw_spin_unlock(&rq->lock);

                if (!remaining)
                        break;
        }
        rcu_read_unlock();

        return starting_runtime - remaining;
}

/*
 * Responsible for refilling a task_group's bandwidth and unthrottling its
 * cfs_rqs as appropriate. If there has been no activity within the last
 * period the timer is deactivated until scheduling resumes; cfs_b->idle is
 * used to track this state.
 */
static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
{
        u64 runtime, runtime_expires;
        int throttled;

        /* no need to continue the timer with no bandwidth constraint */
        if (cfs_b->quota == RUNTIME_INF)
                goto out_deactivate;

        throttled = !list_empty(&cfs_b->throttled_cfs_rq);
        cfs_b->nr_periods += overrun;

        /*
         * idle depends on !throttled (for the case of a large deficit), and if
         * we're going inactive then everything else can be deferred
         */
        if (cfs_b->idle && !throttled)
                goto out_deactivate;

        /*
         * if we have relooped after returning idle once, we need to update our
         * status as actually running, so that other cpus doing
         * __start_cfs_bandwidth will stop trying to cancel us.
         */
        cfs_b->timer_active = 1;

        __refill_cfs_bandwidth_runtime(cfs_b);

        if (!throttled) {
                /* mark as potentially idle for the upcoming period */
                cfs_b->idle = 1;
                return 0;
        }

        /* account preceding periods in which throttling occurred */
        cfs_b->nr_throttled += overrun;

        runtime_expires = cfs_b->runtime_expires;

        /*
         * This check is repeated as we are holding onto the new bandwidth while
         * we unthrottle. This can potentially race with an unthrottled group
         * trying to acquire new bandwidth from the global pool. This can result
         * in us over-using our runtime if it is all used during this loop, but
         * only by limited amounts in that extreme case.
         */
        while (throttled && cfs_b->runtime > 0) {
                runtime = cfs_b->runtime;
                raw_spin_unlock(&cfs_b->lock);
                /* we can't nest cfs_b->lock while distributing bandwidth */
                runtime = distribute_cfs_runtime(cfs_b, runtime,
                                                 runtime_expires);
                raw_spin_lock(&cfs_b->lock);

                throttled = !list_empty(&cfs_b->throttled_cfs_rq);

                cfs_b->runtime -= min(runtime, cfs_b->runtime);
        }

        /*
         * While we are ensured activity in the period following an
         * unthrottle, this also covers the case in which the new bandwidth is
         * insufficient to cover the existing bandwidth deficit.  (Forcing the
         * timer to remain active while there are any throttled entities.)
         */
        cfs_b->idle = 0;

        return 0;

out_deactivate:
        cfs_b->timer_active = 0;
        return 1;
}

/* a cfs_rq won't donate quota below this amount */
static const u64 min_cfs_rq_runtime = 1 * NSEC_PER_MSEC;
/* minimum remaining period time to redistribute slack quota */
static const u64 min_bandwidth_expiration = 2 * NSEC_PER_MSEC;
/* how long we wait to gather additional slack before distributing */
static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;

/*
 * Are we near the end of the current quota period?
 *
 * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
 * hrtimer base being cleared by __hrtimer_start_range_ns. In the case of
 * migrate_hrtimers, base is never cleared, so we are fine.
 */
static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
{
        struct hrtimer *refresh_timer = &cfs_b->period_timer;
        u64 remaining;

        /* if the call-back is running a quota refresh is already occurring */
        if (hrtimer_callback_running(refresh_timer))
                return 1;

        /* is a quota refresh about to occur? */
        remaining = ktime_to_ns(hrtimer_expires_remaining(refresh_timer));
        if (remaining < min_expire)
                return 1;

        return 0;
}

static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
{
        u64 min_left = cfs_bandwidth_slack_period + min_bandwidth_expiration;

        /* if there's a quota refresh soon don't bother with slack */
        if (runtime_refresh_within(cfs_b, min_left))
                return;

        start_bandwidth_timer(&cfs_b->slack_timer,
                                ns_to_ktime(cfs_bandwidth_slack_period));
}

/* we know any runtime found here is valid as update_curr() precedes return */
static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        s64 slack_runtime = cfs_rq->runtime_remaining - min_cfs_rq_runtime;

        if (slack_runtime <= 0)
                return;

        raw_spin_lock(&cfs_b->lock);
        if (cfs_b->quota != RUNTIME_INF &&
            cfs_rq->runtime_expires == cfs_b->runtime_expires) {
                cfs_b->runtime += slack_runtime;

                /* we are under rq->lock, defer unthrottling using a timer */
                if (cfs_b->runtime > sched_cfs_bandwidth_slice() &&
                    !list_empty(&cfs_b->throttled_cfs_rq))
                        start_cfs_slack_bandwidth(cfs_b);
        }
        raw_spin_unlock(&cfs_b->lock);

        /* even if it's not valid for return we don't want to try again */
        cfs_rq->runtime_remaining -= slack_runtime;
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return;

        if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
                return;

        __return_cfs_rq_runtime(cfs_rq);
}

/*
 * This is done with a timer (instead of inline with bandwidth return) since
 * it's necessary to juggle rq->locks to unthrottle their respective cfs_rqs.
 */
static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
{
        u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
        u64 expires;

        /* confirm we're still not at a refresh boundary */
        raw_spin_lock(&cfs_b->lock);
        if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
                raw_spin_unlock(&cfs_b->lock);
                return;
        }

        if (cfs_b->quota != RUNTIME_INF && cfs_b->runtime > slice)
                runtime = cfs_b->runtime;

        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);

        if (!runtime)
                return;

        runtime = distribute_cfs_runtime(cfs_b, runtime, expires);

        raw_spin_lock(&cfs_b->lock);
        if (expires == cfs_b->runtime_expires)
                cfs_b->runtime -= min(runtime, cfs_b->runtime);
        raw_spin_unlock(&cfs_b->lock);
}

/*
 * When a group wakes up we want to make sure that its quota is not already
 * expired/exceeded, otherwise it may be allowed to steal additional ticks of
 * runtime as update_curr() throttling can not not trigger until it's on-rq.
 */
static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return;

        /* an active group must be handled by the update_curr()->put() path */
        if (!cfs_rq->runtime_enabled || cfs_rq->curr)
                return;

        /* ensure the group is not already throttled */
        if (cfs_rq_throttled(cfs_rq))
                return;

        /* update runtime allocation */
        account_cfs_rq_runtime(cfs_rq, 0);
        if (cfs_rq->runtime_remaining <= 0)
                throttle_cfs_rq(cfs_rq);
}

/* conditionally throttle active cfs_rq's from put_prev_entity() */
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return false;

        if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
                return false;

        /*
         * it's possible for a throttled entity to be forced into a running
         * state (e.g. set_curr_task), in this case we're finished.
         */
        if (cfs_rq_throttled(cfs_rq))
                return true;

        throttle_cfs_rq(cfs_rq);
        return true;
}

static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer)
{
        struct cfs_bandwidth *cfs_b =
                container_of(timer, struct cfs_bandwidth, slack_timer);
        do_sched_cfs_slack_timer(cfs_b);

        return HRTIMER_NORESTART;
}

static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
{
        struct cfs_bandwidth *cfs_b =
                container_of(timer, struct cfs_bandwidth, period_timer);
        ktime_t now;
        int overrun;
        int idle = 0;

        raw_spin_lock(&cfs_b->lock);
        for (;;) {
                now = hrtimer_cb_get_time(timer);
                overrun = hrtimer_forward(timer, now, cfs_b->period);

                if (!overrun)
                        break;

                idle = do_sched_cfs_period_timer(cfs_b, overrun);
        }
        raw_spin_unlock(&cfs_b->lock);

        return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}

void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
        raw_spin_lock_init(&cfs_b->lock);
        cfs_b->runtime = 0;
        cfs_b->quota = RUNTIME_INF;
        cfs_b->period = ns_to_ktime(default_cfs_period());

        INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
        hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        cfs_b->period_timer.function = sched_cfs_period_timer;
        hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        cfs_b->slack_timer.function = sched_cfs_slack_timer;
}

static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        cfs_rq->runtime_enabled = 0;
        INIT_LIST_HEAD(&cfs_rq->throttled_list);
}

/* requires cfs_b->lock, may release to reprogram timer */
void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b, bool force)
{
        /*
         * The timer may be active because we're trying to set a new bandwidth
         * period or because we're racing with the tear-down path
         * (timer_active==0 becomes visible before the hrtimer call-back
         * terminates).  In either case we ensure that it's re-programmed
         */
        while (unlikely(hrtimer_active(&cfs_b->period_timer)) &&
               hrtimer_try_to_cancel(&cfs_b->period_timer) < 0) {
                /* bounce the lock to allow do_sched_cfs_period_timer to run */
                raw_spin_unlock(&cfs_b->lock);
                cpu_relax();
                raw_spin_lock(&cfs_b->lock);
                /* if someone else restarted the timer then we're done */
                if (!force && cfs_b->timer_active)
                        return;
        }

        cfs_b->timer_active = 1;
        start_bandwidth_timer(&cfs_b->period_timer, cfs_b->period);
}

static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
        hrtimer_cancel(&cfs_b->period_timer);
        hrtimer_cancel(&cfs_b->slack_timer);
}

static void __maybe_unused update_runtime_enabled(struct rq *rq)
{
        struct cfs_rq *cfs_rq;

        for_each_leaf_cfs_rq(rq, cfs_rq) {
                struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;

                raw_spin_lock(&cfs_b->lock);
                cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
                raw_spin_unlock(&cfs_b->lock);
        }
}

static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
{
        struct cfs_rq *cfs_rq;

        for_each_leaf_cfs_rq(rq, cfs_rq) {
                if (!cfs_rq->runtime_enabled)
                        continue;

                /*
                 * clock_task is not advancing so we just need to make sure
                 * there's some valid quota amount
                 */
                cfs_rq->runtime_remaining = 1;
                /*
                 * Offline rq is schedulable till cpu is completely disabled
                 * in take_cpu_down(), so we prevent new cfs throttling here.
                 */
                cfs_rq->runtime_enabled = 0;

                if (cfs_rq_throttled(cfs_rq))
                        unthrottle_cfs_rq(cfs_rq);
        }
}

#else /* CONFIG_CFS_BANDWIDTH */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
        return rq_clock_task(rq_of(cfs_rq));
}

static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {}
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
        return 0;
}

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
        return 0;
}

static inline int throttled_lb_pair(struct task_group *tg,
                                    int src_cpu, int dest_cpu)
{
        return 0;
}

void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
#endif

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
        return NULL;
}
static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
static inline void update_runtime_enabled(struct rq *rq) {}
static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}

#endif /* CONFIG_CFS_BANDWIDTH */

/**************************************************
 * CFS operations on tasks:
 */

#ifdef CONFIG_SCHED_HRTICK
static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        WARN_ON(task_rq(p) != rq);

        if (cfs_rq->nr_running > 1) {
                u64 slice = sched_slice(cfs_rq, se);
                u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
                s64 delta = slice - ran;

                if (delta < 0) {
                        if (rq->curr == p)
                                resched_task(p);
                        return;
                }

                /*
                 * Don't schedule slices shorter than 10000ns, that just
                 * doesn't make sense. Rely on vruntime for fairness.
                 */
                if (rq->curr != p)
                        delta = max_t(s64, 10000LL, delta);

                hrtick_start(rq, delta);
        }
}

/*
 * called from enqueue/dequeue and updates the hrtick when the
 * current task is from our class and nr_running is low enough
 * to matter.
 */
static void hrtick_update(struct rq *rq)
{
        struct task_struct *curr = rq->curr;

        if (!hrtick_enabled(rq) || curr->sched_class != &fair_sched_class)
                return;

        if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
                hrtick_start_fair(rq, curr);
}
#else /* !CONFIG_SCHED_HRTICK */
static inline void
hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
}

static inline void hrtick_update(struct rq *rq)
{
}
#endif

/*
 * The enqueue_task method is called before nr_running is
 * increased. Here we update the fair scheduling stats and
 * then put the task into the rbtree:
 */
static void
enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;

        for_each_sched_entity(se) {
                if (se->on_rq)
                        break;
                cfs_rq = cfs_rq_of(se);
                enqueue_entity(cfs_rq, se, flags);

                /*
                 * end evaluation on encountering a throttled cfs_rq
                 *
                 * note: in the case of encountering a throttled cfs_rq we will
                 * post the final h_nr_running increment below.
                */
                if (cfs_rq_throttled(cfs_rq))
                        break;
                cfs_rq->h_nr_running++;

                flags = ENQUEUE_WAKEUP;
        }

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                cfs_rq->h_nr_running++;

                if (cfs_rq_throttled(cfs_rq))
                        break;

                update_cfs_shares(cfs_rq);
                update_entity_load_avg(se, 1);
        }

        if (!se) {
                update_rq_runnable_avg(rq, rq->nr_running);
                add_nr_running(rq, 1);
        }
        hrtick_update(rq);
}

static void set_next_buddy(struct sched_entity *se);

/*
 * The dequeue_task method is called before nr_running is
 * decreased. We remove the task from the rbtree and
 * update the fair scheduling stats:
 */
static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;
        int task_sleep = flags & DEQUEUE_SLEEP;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                dequeue_entity(cfs_rq, se, flags);

                /*
                 * end evaluation on encountering a throttled cfs_rq
                 *
                 * note: in the case of encountering a throttled cfs_rq we will
                 * post the final h_nr_running decrement below.
                */
                if (cfs_rq_throttled(cfs_rq))
                        break;
                cfs_rq->h_nr_running--;

                /* Don't dequeue parent if it has other entities besides us */
                if (cfs_rq->load.weight) {
                        /*
                         * Bias pick_next to pick a task from this cfs_rq, as
                         * p is sleeping when it is within its sched_slice.
                         */
                        if (task_sleep && parent_entity(se))
                                set_next_buddy(parent_entity(se));

                        /* avoid re-evaluating load for this entity */
                        se = parent_entity(se);
                        break;
                }
                flags |= DEQUEUE_SLEEP;
        }

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                cfs_rq->h_nr_running--;

                if (cfs_rq_throttled(cfs_rq))
                        break;

                update_cfs_shares(cfs_rq);
                update_entity_load_avg(se, 1);
        }

        if (!se) {
                sub_nr_running(rq, 1);
                update_rq_runnable_avg(rq, 1);
        }
        hrtick_update(rq);
}

#ifdef CONFIG_SMP
/* Used instead of source_load when we know the type == 0 */
static unsigned long weighted_cpuload(const int cpu)
{
        return cpu_rq(cpu)->cfs.runnable_load_avg;
}

/*
 * Return a low guess at the load of a migration-source cpu weighted
 * according to the scheduling class and "nice" value.
 *
 * We want to under-estimate the load of migration sources, to
 * balance conservatively.
 */
static unsigned long source_load(int cpu, int type)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long total = weighted_cpuload(cpu);

        if (type == 0 || !sched_feat(LB_BIAS))
                return total;

        return min(rq->cpu_load[type-1], total);
}

/*
 * Return a high guess at the load of a migration-target cpu weighted
 * according to the scheduling class and "nice" value.
 */
static unsigned long target_load(int cpu, int type)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long total = weighted_cpuload(cpu);

        if (type == 0 || !sched_feat(LB_BIAS))
                return total;

        return max(rq->cpu_load[type-1], total);
}

static unsigned long capacity_of(int cpu)
{
        return cpu_rq(cpu)->cpu_capacity;
}

static unsigned long cpu_avg_load_per_task(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long nr_running = ACCESS_ONCE(rq->nr_running);
        unsigned long load_avg = rq->cfs.runnable_load_avg;

        if (nr_running)
                return load_avg / nr_running;

        return 0;
}

static void record_wakee(struct task_struct *p)
{
        /*
         * Rough decay (wiping) for cost saving, don't worry
         * about the boundary, really active task won't care
         * about the loss.
         */
        if (time_after(jiffies, current->wakee_flip_decay_ts + HZ)) {
                current->wakee_flips >>= 1;
                current->wakee_flip_decay_ts = jiffies;
        }

        if (current->last_wakee != p) {
                current->last_wakee = p;
                current->wakee_flips++;
        }
}

static void task_waking_fair(struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        u64 min_vruntime;

#ifndef CONFIG_64BIT
        u64 min_vruntime_copy;

        do {
                min_vruntime_copy = cfs_rq->min_vruntime_copy;
                smp_rmb();
                min_vruntime = cfs_rq->min_vruntime;
        } while (min_vruntime != min_vruntime_copy);
#else
        min_vruntime = cfs_rq->min_vruntime;
#endif

        se->vruntime -= min_vruntime;
        record_wakee(p);
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
 * effective_load() calculates the load change as seen from the root_task_group
 *
 * Adding load to a group doesn't make a group heavier, but can cause movement
 * of group shares between cpus. Assuming the shares were perfectly aligned one
 * can calculate the shift in shares.
 *
 * Calculate the effective load difference if @wl is added (subtracted) to @tg
 * on this @cpu and results in a total addition (subtraction) of @wg to the
 * total group weight.
 *
 * Given a runqueue weight distribution (rw_i) we can compute a shares
 * distribution (s_i) using:
 *
 *   s_i = rw_i / \Sum rw_j                                             (1)
 *
 * Suppose we have 4 CPUs and our @tg is a direct child of the root group and
 * has 7 equal weight tasks, distributed as below (rw_i), with the resulting
 * shares distribution (s_i):
 *
 *   rw_i = {   2,   4,   1,   0 }
 *   s_i  = { 2/7, 4/7, 1/7,   0 }
 *
 * As per wake_affine() we're interested in the load of two CPUs (the CPU the
 * task used to run on and the CPU the waker is running on), we need to
 * compute the effect of waking a task on either CPU and, in case of a sync
 * wakeup, compute the effect of the current task going to sleep.
 *
 * So for a change of @wl to the local @cpu with an overall group weight change
 * of @wl we can compute the new shares distribution (s'_i) using:
 *
 *   s'_i = (rw_i + @wl) / (@wg + \Sum rw_j)                            (2)
 *
 * Suppose we're interested in CPUs 0 and 1, and want to compute the load
 * differences in waking a task to CPU 0. The additional task changes the
 * weight and shares distributions like:
 *
 *   rw'_i = {   3,   4,   1,   0 }
 *   s'_i  = { 3/8, 4/8, 1/8,   0 }
 *
 * We can then compute the difference in effective weight by using:
 *
 *   dw_i = S * (s'_i - s_i)                                            (3)
 *
 * Where 'S' is the group weight as seen by its parent.
 *
 * Therefore the effective change in loads on CPU 0 would be 5/56 (3/8 - 2/7)
 * times the weight of the group. The effect on CPU 1 would be -4/56 (4/8 -
 * 4/7) times the weight of the group.
 */
static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
{
        struct sched_entity *se = tg->se[cpu];

        if (!tg->parent)        /* the trivial, non-cgroup case */
                return wl;

        for_each_sched_entity(se) {
                long w, W;

                tg = se->my_q->tg;

                /*
                 * W = @wg + \Sum rw_j
                 */
                W = wg + calc_tg_weight(tg, se->my_q);

                /*
                 * w = rw_i + @wl
                 */
                w = se->my_q->load.weight + wl;

                /*
                 * wl = S * s'_i; see (2)
                 */
                if (W > 0 && w < W)
                        wl = (w * tg->shares) / W;
                else
                        wl = tg->shares;

                /*
                 * Per the above, wl is the new se->load.weight value; since
                 * those are clipped to [MIN_SHARES, ...) do so now. See
                 * calc_cfs_shares().
                 */
                if (wl < MIN_SHARES)
                        wl = MIN_SHARES;

                /*
                 * wl = dw_i = S * (s'_i - s_i); see (3)
                 */
                wl -= se->load.weight;

                /*
                 * Recursively apply this logic to all parent groups to compute
                 * the final effective load change on the root group. Since
                 * only the @tg group gets extra weight, all parent groups can
                 * only redistribute existing shares. @wl is the shift in shares
                 * resulting from this level per the above.
                 */
                wg = 0;
        }

        return wl;
}
#else

static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
{
        return wl;
}

#endif

static int wake_wide(struct task_struct *p)
{
        int factor = this_cpu_read(sd_llc_size);

        /*
         * Yeah, it's the switching-frequency, could means many wakee or
         * rapidly switch, use factor here will just help to automatically
         * adjust the loose-degree, so bigger node will lead to more pull.
         */
        if (p->wakee_flips > factor) {
                /*
                 * wakee is somewhat hot, it needs certain amount of cpu
                 * resource, so if waker is far more hot, prefer to leave
                 * it alone.
                 */
                if (current->wakee_flips > (factor * p->wakee_flips))
                        return 1;
        }

        return 0;
}

static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
{
        s64 this_load, load;
        int idx, this_cpu, prev_cpu;
        unsigned long tl_per_task;
        struct task_group *tg;
        unsigned long weight;
        int balanced;

        /*
         * If we wake multiple tasks be careful to not bounce
         * ourselves around too much.
         */
        if (wake_wide(p))
                return 0;

        idx       = sd->wake_idx;
        this_cpu  = smp_processor_id();
        prev_cpu  = task_cpu(p);
        load      = source_load(prev_cpu, idx);
        this_load = target_load(this_cpu, idx);

        /*
         * If sync wakeup then subtract the (maximum possible)
         * effect of the currently running task from the load
         * of the current CPU:
         */
        if (sync) {
                tg = task_group(current);
                weight = current->se.load.weight;

                this_load += effective_load(tg, this_cpu, -weight, -weight);
                load += effective_load(tg, prev_cpu, 0, -weight);
        }

        tg = task_group(p);
        weight = p->se.load.weight;

        /*
         * In low-load situations, where prev_cpu is idle and this_cpu is idle
         * due to the sync cause above having dropped this_load to 0, we'll
         * always have an imbalance, but there's really nothing you can do
         * about that, so that's good too.
         *
         * Otherwise check if either cpus are near enough in load to allow this
         * task to be woken on this_cpu.
         */
        if (this_load > 0) {
                s64 this_eff_load, prev_eff_load;

                this_eff_load = 100;
                this_eff_load *= capacity_of(prev_cpu);
                this_eff_load *= this_load +
                        effective_load(tg, this_cpu, weight, weight);

                prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
                prev_eff_load *= capacity_of(this_cpu);
                prev_eff_load *= load + effective_load(tg, prev_cpu, 0, weight);

                balanced = this_eff_load <= prev_eff_load;
        } else
                balanced = true;

        /*
         * If the currently running task will sleep within
         * a reasonable amount of time then attract this newly
         * woken task:
         */
        if (sync && balanced)
                return 1;

        schedstat_inc(p, se.statistics.nr_wakeups_affine_attempts);
        tl_per_task = cpu_avg_load_per_task(this_cpu);

        if (balanced ||
            (this_load <= load &&
             this_load + target_load(prev_cpu, idx) <= tl_per_task)) {
                /*
                 * This domain has SD_WAKE_AFFINE and
                 * p is cache cold in this domain, and
                 * there is no bad imbalance.
                 */
                schedstat_inc(sd, ttwu_move_affine);
                schedstat_inc(p, se.statistics.nr_wakeups_affine);

                return 1;
        }
        return 0;
}

/*
 * find_idlest_group finds and returns the least busy CPU group within the
 * domain.
 */
static struct sched_group *
find_idlest_group(struct sched_domain *sd, struct task_struct *p,
                  int this_cpu, int sd_flag)
{
        struct sched_group *idlest = NULL, *group = sd->groups;
        unsigned long min_load = ULONG_MAX, this_load = 0;
        int load_idx = sd->forkexec_idx;
        int imbalance = 100 + (sd->imbalance_pct-100)/2;

        if (sd_flag & SD_BALANCE_WAKE)
                load_idx = sd->wake_idx;

        do {
                unsigned long load, avg_load;
                int local_group;
                int i;

                /* Skip over this group if it has no CPUs allowed */
                if (!cpumask_intersects(sched_group_cpus(group),
                                        tsk_cpus_allowed(p)))
                        continue;

                local_group = cpumask_test_cpu(this_cpu,
                                               sched_group_cpus(group));

                /* Tally up the load of all CPUs in the group */
                avg_load = 0;

                for_each_cpu(i, sched_group_cpus(group)) {
                        /* Bias balancing toward cpus of our domain */
                        if (local_group)
                                load = source_load(i, load_idx);
                        else
                                load = target_load(i, load_idx);

                        avg_load += load;
                }

                /* Adjust by relative CPU capacity of the group */
                avg_load = (avg_load * SCHED_CAPACITY_SCALE) / group->sgc->capacity;

                if (local_group) {
                        this_load = avg_load;
                } else if (avg_load < min_load) {
                        min_load = avg_load;
                        idlest = group;
                }
        } while (group = group->next, group != sd->groups);

        if (!idlest || 100*this_load < imbalance*min_load)
                return NULL;
        return idlest;
}

/*
 * find_idlest_cpu - find the idlest cpu among the cpus in group.
 */
static int
find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
{
        unsigned long load, min_load = ULONG_MAX;
        int idlest = -1;
        int i;

        /* Traverse only the allowed CPUs */
        for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
                load = weighted_cpuload(i);

                if (load < min_load || (load == min_load && i == this_cpu)) {
                        min_load = load;
                        idlest = i;
                }
        }

        return idlest;
}

/*
 * Try and locate an idle CPU in the sched_domain.
 */
static int select_idle_sibling(struct task_struct *p, int target)
{
        struct sched_domain *sd;
        struct sched_group *sg;
        int i = task_cpu(p);

        if (idle_cpu(target))
                return target;

        /*
         * If the prevous cpu is cache affine and idle, don't be stupid.
         */
        if (i != target && cpus_share_cache(i, target) && idle_cpu(i))
                return i;

        /*
         * Otherwise, iterate the domains and find an elegible idle cpu.
         */
        sd = rcu_dereference(per_cpu(sd_llc, target));
        for_each_lower_domain(sd) {
                sg = sd->groups;
                do {
                        if (!cpumask_intersects(sched_group_cpus(sg),
                                                tsk_cpus_allowed(p)))
                                goto next;

                        for_each_cpu(i, sched_group_cpus(sg)) {
                                if (i == target || !idle_cpu(i))
                                        goto next;
                        }

                        target = cpumask_first_and(sched_group_cpus(sg),
                                        tsk_cpus_allowed(p));
                        goto done;
next:
                        sg = sg->next;
                } while (sg != sd->groups);
        }
done:
        return target;
}

/*
 * select_task_rq_fair: Select target runqueue for the waking task in domains
 * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
 * SD_BALANCE_FORK, or SD_BALANCE_EXEC.
 *
 * Balances load by selecting the idlest cpu in the idlest group, or under
 * certain conditions an idle sibling cpu if the domain has SD_WAKE_AFFINE set.
 *
 * Returns the target cpu number.
 *
 * preempt must be disabled.
 */
static int
select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
{
        struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
        int cpu = smp_processor_id();
        int new_cpu = cpu;
        int want_affine = 0;
        int sync = wake_flags & WF_SYNC;

        if (p->nr_cpus_allowed == 1)
                return prev_cpu;

        if (sd_flag & SD_BALANCE_WAKE) {
                if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p)))
                        want_affine = 1;
                new_cpu = prev_cpu;
        }

        rcu_read_lock();
        for_each_domain(cpu, tmp) {
                if (!(tmp->flags & SD_LOAD_BALANCE))
                        continue;

                /*
                 * If both cpu and prev_cpu are part of this domain,
                 * cpu is a valid SD_WAKE_AFFINE target.
                 */
                if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
                    cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
                        affine_sd = tmp;
                        break;
                }

                if (tmp->flags & sd_flag)
                        sd = tmp;
        }

        if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync))
                prev_cpu = cpu;

        if (sd_flag & SD_BALANCE_WAKE) {
                new_cpu = select_idle_sibling(p, prev_cpu);
                goto unlock;
        }

        while (sd) {
                struct sched_group *group;
                int weight;

                if (!(sd->flags & sd_flag)) {
                        sd = sd->child;
                        continue;
                }

                group = find_idlest_group(sd, p, cpu, sd_flag);
                if (!group) {
                        sd = sd->child;
                        continue;
                }

                new_cpu = find_idlest_cpu(group, p, cpu);
                if (new_cpu == -1 || new_cpu == cpu) {
                        /* Now try balancing at a lower domain level of cpu */
                        sd = sd->child;
                        continue;
                }

                /* Now try balancing at a lower domain level of new_cpu */
                cpu = new_cpu;
                weight = sd->span_weight;
                sd = NULL;
                for_each_domain(cpu, tmp) {
                        if (weight <= tmp->span_weight)
                                break;
                        if (tmp->flags & sd_flag)
                                sd = tmp;
                }
                /* while loop will break here if sd == NULL */
        }
unlock:
        rcu_read_unlock();

        return new_cpu;
}

/*
 * Called immediately before a task is migrated to a new cpu; task_cpu(p) and
 * cfs_rq_of(p) references at time of call are still valid and identify the
 * previous cpu.  However, the caller only guarantees p->pi_lock is held; no
 * other assumptions, including the state of rq->lock, should be made.
 */
static void
migrate_task_rq_fair(struct task_struct *p, int next_cpu)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        /*
         * Load tracking: accumulate removed load so that it can be processed
         * when we next update owning cfs_rq under rq->lock.  Tasks contribute
         * to blocked load iff they have a positive decay-count.  It can never
         * be negative here since on-rq tasks have decay-count == 0.
         */
        if (se->avg.decay_count) {
                se->avg.decay_count = -__synchronize_entity_decay(se);
                atomic_long_add(se->avg.load_avg_contrib,
                                                &cfs_rq->removed_load);
        }

        /* We have migrated, no longer consider this task hot */
        se->exec_start = 0;
}
#endif /* CONFIG_SMP */

static unsigned long
wakeup_gran(struct sched_entity *curr, struct sched_entity *se)
{
        unsigned long gran = sysctl_sched_wakeup_granularity;

        /*
         * Since its curr running now, convert the gran from real-time
         * to virtual-time in his units.
         *
         * By using 'se' instead of 'curr' we penalize light tasks, so
         * they get preempted easier. That is, if 'se' < 'curr' then
         * the resulting gran will be larger, therefore penalizing the
         * lighter, if otoh 'se' > 'curr' then the resulting gran will
         * be smaller, again penalizing the lighter task.
         *
         * This is especially important for buddies when the leftmost
         * task is higher priority than the buddy.
         */
        return calc_delta_fair(gran, se);
}

/*
 * Should 'se' preempt 'curr'.
 *
 *             |s1
 *        |s2
 *   |s3
 *         g
 *      |<--->|c
 *
 *  w(c, s1) = -1
 *  w(c, s2) =  0
 *  w(c, s3) =  1
 *
 */
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
        s64 gran, vdiff = curr->vruntime - se->vruntime;

        if (vdiff <= 0)
                return -1;

        gran = wakeup_gran(curr, se);
        if (vdiff > gran)
                return 1;

        return 0;
}

static void set_last_buddy(struct sched_entity *se)
{
        if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
                return;

        for_each_sched_entity(se)
                cfs_rq_of(se)->last = se;
}

static void set_next_buddy(struct sched_entity *se)
{
        if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
                return;

        for_each_sched_entity(se)
                cfs_rq_of(se)->next = se;
}

static void set_skip_buddy(struct sched_entity *se)
{
        for_each_sched_entity(se)
                cfs_rq_of(se)->skip = se;
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
{
        struct task_struct *curr = rq->curr;
        struct sched_entity *se = &curr->se, *pse = &p->se;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
        int scale = cfs_rq->nr_running >= sched_nr_latency;
        int next_buddy_marked = 0;

        if (unlikely(se == pse))
                return;

        /*
         * This is possible from callers such as move_task(), in which we
         * unconditionally check_prempt_curr() after an enqueue (which may have
         * lead to a throttle).  This both saves work and prevents false
         * next-buddy nomination below.
         */
        if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
                return;

        if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
                set_next_buddy(pse);
                next_buddy_marked = 1;
        }

        /*
         * We can come here with TIF_NEED_RESCHED already set from new task
         * wake up path.
         *
         * Note: this also catches the edge-case of curr being in a throttled
         * group (e.g. via set_curr_task), since update_curr() (in the
         * enqueue of curr) will have resulted in resched being set.  This
         * prevents us from potentially nominating it as a false LAST_BUDDY
         * below.
         */
        if (test_tsk_need_resched(curr))
                return;

        /* Idle tasks are by definition preempted by non-idle tasks. */
        if (unlikely(curr->policy == SCHED_IDLE) &&
            likely(p->policy != SCHED_IDLE))
                goto preempt;

        /*
         * Batch and idle tasks do not preempt non-idle tasks (their preemption
         * is driven by the tick):
         */
        if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
                return;

        find_matching_se(&se, &pse);
        update_curr(cfs_rq_of(se));
        BUG_ON(!pse);
        if (wakeup_preempt_entity(se, pse) == 1) {
                /*
                 * Bias pick_next to pick the sched entity that is
                 * triggering this preemption.
                 */
                if (!next_buddy_marked)
                        set_next_buddy(pse);
                goto preempt;
        }

        return;

preempt:
        resched_task(curr);
        /*
         * Only set the backward buddy when the current task is still
         * on the rq. This can happen when a wakeup gets interleaved
         * with schedule on the ->pre_schedule() or idle_balance()
         * point, either of which can * drop the rq lock.
         *
         * Also, during early boot the idle thread is in the fair class,
         * for obvious reasons its a bad idea to schedule back to it.
         */
        if (unlikely(!se->on_rq || curr == rq->idle))
                return;

        if (sched_feat(LAST_BUDDY) && scale && entity_is_task(se))
                set_last_buddy(se);
}

static struct task_struct *
pick_next_task_fair(struct rq *rq, struct task_struct *prev)
{
        struct cfs_rq *cfs_rq = &rq->cfs;
        struct sched_entity *se;
        struct task_struct *p;
        int new_tasks;

again:
#ifdef CONFIG_FAIR_GROUP_SCHED
        if (!cfs_rq->nr_running)
                goto idle;

        if (prev->sched_class != &fair_sched_class)
                goto simple;

        /*
         * Because of the set_next_buddy() in dequeue_task_fair() it is rather
         * likely that a next task is from the same cgroup as the current.
         *
         * Therefore attempt to avoid putting and setting the entire cgroup
         * hierarchy, only change the part that actually changes.
         */

        do {
                struct sched_entity *curr = cfs_rq->curr;

                /*
                 * Since we got here without doing put_prev_entity() we also
                 * have to consider cfs_rq->curr. If it is still a runnable
                 * entity, update_curr() will update its vruntime, otherwise
                 * forget we've ever seen it.
                 */
                if (curr && curr->on_rq)
                        update_curr(cfs_rq);
                else
                        curr = NULL;

                /*
                 * This call to check_cfs_rq_runtime() will do the throttle and
                 * dequeue its entity in the parent(s). Therefore the 'simple'
                 * nr_running test will indeed be correct.
                 */
                if (unlikely(check_cfs_rq_runtime(cfs_rq)))
                        goto simple;

                se = pick_next_entity(cfs_rq, curr);
                cfs_rq = group_cfs_rq(se);
        } while (cfs_rq);

        p = task_of(se);

        /*
         * Since we haven't yet done put_prev_entity and if the selected task
         * is a different task than we started out with, try and touch the
         * least amount of cfs_rqs.
         */
        if (prev != p) {
                struct sched_entity *pse = &prev->se;

                while (!(cfs_rq = is_same_group(se, pse))) {
                        int se_depth = se->depth;
                        int pse_depth = pse->depth;

                        if (se_depth <= pse_depth) {
                                put_prev_entity(cfs_rq_of(pse), pse);
                                pse = parent_entity(pse);
                        }
                        if (se_depth >= pse_depth) {
                                set_next_entity(cfs_rq_of(se), se);
                                se = parent_entity(se);
                        }
                }

                put_prev_entity(cfs_rq, pse);
                set_next_entity(cfs_rq, se);
        }

        if (hrtick_enabled(rq))
                hrtick_start_fair(rq, p);

        return p;
simple:
        cfs_rq = &rq->cfs;
#endif

        if (!cfs_rq->nr_running)
                goto idle;

        put_prev_task(rq, prev);

        do {
                se = pick_next_entity(cfs_rq, NULL);
                set_next_entity(cfs_rq, se);
                cfs_rq = group_cfs_rq(se);
        } while (cfs_rq);

        p = task_of(se);

        if (hrtick_enabled(rq))
                hrtick_start_fair(rq, p);

        return p;

idle:
        new_tasks = idle_balance(rq);
        /*
         * Because idle_balance() releases (and re-acquires) rq->lock, it is
         * possible for any higher priority task to appear. In that case we
         * must re-start the pick_next_entity() loop.
         */
        if (new_tasks < 0)
                return RETRY_TASK;

        if (new_tasks > 0)
                goto again;

        return NULL;
}

/*
 * Account for a descheduled task:
 */
static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
{
        struct sched_entity *se = &prev->se;
        struct cfs_rq *cfs_rq;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                put_prev_entity(cfs_rq, se);
        }
}

/*
 * sched_yield() is very simple
 *
 * The magic of dealing with the ->skip buddy is in pick_next_entity.
 */
static void yield_task_fair(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
        struct sched_entity *se = &curr->se;

        /*
         * Are we the only task in the tree?
         */
        if (unlikely(rq->nr_running == 1))
                return;

        clear_buddies(cfs_rq, se);

        if (curr->policy != SCHED_BATCH) {
                update_rq_clock(rq);
                /*
                 * Update run-time statistics of the 'current'.
                 */
                update_curr(cfs_rq);
                /*
                 * Tell update_rq_clock() that we've just updated,
                 * so we don't do microscopic update in schedule()
                 * and double the fastpath cost.
                 */
                 rq->skip_clock_update = 1;
        }

        set_skip_buddy(se);
}

static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)
{
        struct sched_entity *se = &p->se;

        /* throttled hierarchies are not runnable */
        if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))
                return false;

        /* Tell the scheduler that we'd really like pse to run next. */
        set_next_buddy(se);

        yield_task_fair(rq);

        return true;
}

#ifdef CONFIG_SMP
/**************************************************
 * Fair scheduling class load-balancing methods.
 *
 * BASICS
 *
 * The purpose of load-balancing is to achieve the same basic fairness the
 * per-cpu scheduler provides, namely provide a proportional amount of compute
 * time to each task. This is expressed in the following equation:
 *
 *   W_i,n/P_i == W_j,n/P_j for all i,j                               (1)
 *
 * Where W_i,n is the n-th weight average for cpu i. The instantaneous weight
 * W_i,0 is defined as:
 *
 *   W_i,0 = \Sum_j w_i,j                                             (2)
 *
 * Where w_i,j is the weight of the j-th runnable task on cpu i. This weight
 * is derived from the nice value as per prio_to_weight[].
 *
 * The weight average is an exponential decay average of the instantaneous
 * weight:
 *
 *   W'_i,n = (2^n - 1) / 2^n * W_i,n + 1 / 2^n * W_i,0               (3)
 *
 * C_i is the compute capacity of cpu i, typically it is the
 * fraction of 'recent' time available for SCHED_OTHER task execution. But it
 * can also include other factors [XXX].
 *
 * To achieve this balance we define a measure of imbalance which follows
 * directly from (1):
 *
 *   imb_i,j = max{ avg(W/C), W_i/C_i } - min{ avg(W/C), W_j/C_j }    (4)
 *
 * We them move tasks around to minimize the imbalance. In the continuous
 * function space it is obvious this converges, in the discrete case we get
 * a few fun cases generally called infeasible weight scenarios.
 *
 * [XXX expand on:
 *     - infeasible weights;
 *     - local vs global optima in the discrete case. ]
 *
 *
 * SCHED DOMAINS
 *
 * In order to solve the imbalance equation (4), and avoid the obvious O(n^2)
 * for all i,j solution, we create a tree of cpus that follows the hardware
 * topology where each level pairs two lower groups (or better). This results
 * in O(log n) layers. Furthermore we reduce the number of cpus going up the
 * tree to only the first of the previous level and we decrease the frequency
 * of load-balance at each level inv. proportional to the number of cpus in
 * the groups.
 *
 * This yields:
 *
 *     log_2 n     1     n
 *   \Sum       { --- * --- * 2^i } = O(n)                            (5)
 *     i = 0      2^i   2^i
 *                               `- size of each group
 *         |         |     `- number of cpus doing load-balance
 *         |         `- freq
 *         `- sum over all levels
 *
 * Coupled with a limit on how many tasks we can migrate every balance pass,
 * this makes (5) the runtime complexity of the balancer.
 *
 * An important property here is that each CPU is still (indirectly) connected
 * to every other cpu in at most O(log n) steps:
 *
 * The adjacency matrix of the resulting graph is given by:
 *
 *             log_2 n     
 *   A_i,j = \Union     (i % 2^k == 0) && i / 2^(k+1) == j / 2^(k+1)  (6)
 *             k = 0
 *
 * And you'll find that:
 *
 *   A^(log_2 n)_i,j != 0  for all i,j                                (7)
 *
 * Showing there's indeed a path between every cpu in at most O(log n) steps.
 * The task movement gives a factor of O(m), giving a convergence complexity
 * of:
 *
 *   O(nm log n),  n := nr_cpus, m := nr_tasks                        (8)
 *
 *
 * WORK CONSERVING
 *
 * In order to avoid CPUs going idle while there's still work to do, new idle
 * balancing is more aggressive and has the newly idle cpu iterate up the domain
 * tree itself instead of relying on other CPUs to bring it work.
 *
 * This adds some complexity to both (5) and (8) but it reduces the total idle
 * time.
 *
 * [XXX more?]
 *
 *
 * CGROUPS
 *
 * Cgroups make a horror show out of (2), instead of a simple sum we get:
 *
 *                                s_k,i
 *   W_i,0 = \Sum_j \Prod_k w_k * -----                               (9)
 *                                 S_k
 *
 * Where
 *
 *   s_k,i = \Sum_j w_i,j,k  and  S_k = \Sum_i s_k,i                 (10)
 *
 * w_i,j,k is the weight of the j-th runnable task in the k-th cgroup on cpu i.
 *
 * The big problem is S_k, its a global sum needed to compute a local (W_i)
 * property.
 *
 * [XXX write more on how we solve this.. _after_ merging pjt's patches that
 *      rewrite all of this once again.]
 */ 

static unsigned long __read_mostly max_load_balance_interval = HZ/10;

enum fbq_type { regular, remote, all };

#define LBF_ALL_PINNED  0x01
#define LBF_NEED_BREAK  0x02
#define LBF_DST_PINNED  0x04
#define LBF_SOME_PINNED 0x08

struct lb_env {
        struct sched_domain     *sd;

        struct rq               *src_rq;
        int                     src_cpu;

        int                     dst_cpu;
        struct rq               *dst_rq;

        struct cpumask          *dst_grpmask;
        int                     new_dst_cpu;
        enum cpu_idle_type      idle;
        long                    imbalance;
        /* The set of CPUs under consideration for load-balancing */
        struct cpumask          *cpus;

        unsigned int            flags;

        unsigned int            loop;
        unsigned int            loop_break;
        unsigned int            loop_max;

        enum fbq_type           fbq_type;
};

/*
 * move_task - move a task from one runqueue to another runqueue.
 * Both runqueues must be locked.
 */
static void move_task(struct task_struct *p, struct lb_env *env)
{
        deactivate_task(env->src_rq, p, 0);
        set_task_cpu(p, env->dst_cpu);
        activate_task(env->dst_rq, p, 0);
        check_preempt_curr(env->dst_rq, p, 0);
}

/*
 * Is this task likely cache-hot:
 */
static int task_hot(struct task_struct *p, struct lb_env *env)
{
        s64 delta;

        if (p->sched_class != &fair_sched_class)
                return 0;

        if (unlikely(p->policy == SCHED_IDLE))
                return 0;

        /*
         * Buddy candidates are cache hot:
         */
        if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running &&
                        (&p->se == cfs_rq_of(&p->se)->next ||
                         &p->se == cfs_rq_of(&p->se)->last))
                return 1;

        if (sysctl_sched_migration_cost == -1)
                return 1;
        if (sysctl_sched_migration_cost == 0)
                return 0;

        delta = rq_clock_task(env->src_rq) - p->se.exec_start;

        return delta < (s64)sysctl_sched_migration_cost;
}

#ifdef CONFIG_NUMA_BALANCING
/* Returns true if the destination node has incurred more faults */
static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
{
        struct numa_group *numa_group = rcu_dereference(p->numa_group);
        int src_nid, dst_nid;

        if (!sched_feat(NUMA_FAVOUR_HIGHER) || !p->numa_faults_memory ||
            !(env->sd->flags & SD_NUMA)) {
                return false;
        }

        src_nid = cpu_to_node(env->src_cpu);
        dst_nid = cpu_to_node(env->dst_cpu);

        if (src_nid == dst_nid)
                return false;

        if (numa_group) {
                /* Task is already in the group's interleave set. */
                if (node_isset(src_nid, numa_group->active_nodes))
                        return false;

                /* Task is moving into the group's interleave set. */
                if (node_isset(dst_nid, numa_group->active_nodes))
                        return true;

                return group_faults(p, dst_nid) > group_faults(p, src_nid);
        }

        /* Encourage migration to the preferred node. */
        if (dst_nid == p->numa_preferred_nid)
                return true;

        return task_faults(p, dst_nid) > task_faults(p, src_nid);
}


static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
{
        struct numa_group *numa_group = rcu_dereference(p->numa_group);
        int src_nid, dst_nid;

        if (!sched_feat(NUMA) || !sched_feat(NUMA_RESIST_LOWER))
                return false;

        if (!p->numa_faults_memory || !(env->sd->flags & SD_NUMA))
                return false;

        src_nid = cpu_to_node(env->src_cpu);
        dst_nid = cpu_to_node(env->dst_cpu);

        if (src_nid == dst_nid)
                return false;

        if (numa_group) {
                /* Task is moving within/into the group's interleave set. */
                if (node_isset(dst_nid, numa_group->active_nodes))
                        return false;

                /* Task is moving out of the group's interleave set. */
                if (node_isset(src_nid, numa_group->active_nodes))
                        return true;

                return group_faults(p, dst_nid) < group_faults(p, src_nid);
        }

        /* Migrating away from the preferred node is always bad. */
        if (src_nid == p->numa_preferred_nid)
                return true;

        return task_faults(p, dst_nid) < task_faults(p, src_nid);
}

#else
static inline bool migrate_improves_locality(struct task_struct *p,
                                             struct lb_env *env)
{
        return false;
}

static inline bool migrate_degrades_locality(struct task_struct *p,
                                             struct lb_env *env)
{
        return false;
}
#endif

/*
 * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
 */
static
int can_migrate_task(struct task_struct *p, struct lb_env *env)
{
        int tsk_cache_hot = 0;
        /*
         * We do not migrate tasks that are:
         * 1) throttled_lb_pair, or
         * 2) cannot be migrated to this CPU due to cpus_allowed, or
         * 3) running (obviously), or
         * 4) are cache-hot on their current CPU.
         */
        if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
                return 0;

        if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {
                int cpu;

                schedstat_inc(p, se.statistics.nr_failed_migrations_affine);

                env->flags |= LBF_SOME_PINNED;

                /*
                 * Remember if this task can be migrated to any other cpu in
                 * our sched_group. We may want to revisit it if we couldn't
                 * meet load balance goals by pulling other tasks on src_cpu.
                 *
                 * Also avoid computing new_dst_cpu if we have already computed
                 * one in current iteration.
                 */
                if (!env->dst_grpmask || (env->flags & LBF_DST_PINNED))
                        return 0;

                /* Prevent to re-select dst_cpu via env's cpus */
                for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {
                        if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) {
                                env->flags |= LBF_DST_PINNED;
                                env->new_dst_cpu = cpu;
                                break;
                        }
                }

                return 0;
        }

        /* Record that we found atleast one task that could run on dst_cpu */
        env->flags &= ~LBF_ALL_PINNED;

        if (task_running(env->src_rq, p)) {
                schedstat_inc(p, se.statistics.nr_failed_migrations_running);
                return 0;
        }

        /*
         * Aggressive migration if:
         * 1) destination numa is preferred
         * 2) task is cache cold, or
         * 3) too many balance attempts have failed.
         */
        tsk_cache_hot = task_hot(p, env);
        if (!tsk_cache_hot)
                tsk_cache_hot = migrate_degrades_locality(p, env);

        if (migrate_improves_locality(p, env)) {
#ifdef CONFIG_SCHEDSTATS
                if (tsk_cache_hot) {
                        schedstat_inc(env->sd, lb_hot_gained[env->idle]);
                        schedstat_inc(p, se.statistics.nr_forced_migrations);
                }
#endif
                return 1;
        }

        if (!tsk_cache_hot ||
                env->sd->nr_balance_failed > env->sd->cache_nice_tries) {

                if (tsk_cache_hot) {
                        schedstat_inc(env->sd, lb_hot_gained[env->idle]);
                        schedstat_inc(p, se.statistics.nr_forced_migrations);
                }

                return 1;
        }

        schedstat_inc(p, se.statistics.nr_failed_migrations_hot);
        return 0;
}

/*
 * move_one_task tries to move exactly one task from busiest to this_rq, as
 * part of active balancing operations within "domain".
 * Returns 1 if successful and 0 otherwise.
 *
 * Called with both runqueues locked.
 */
static int move_one_task(struct lb_env *env)
{
        struct task_struct *p, *n;

        list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {
                if (!can_migrate_task(p, env))
                        continue;

                move_task(p, env);
                /*
                 * Right now, this is only the second place move_task()
                 * is called, so we can safely collect move_task()
                 * stats here rather than inside move_task().
                 */
                schedstat_inc(env->sd, lb_gained[env->idle]);
                return 1;
        }
        return 0;
}

static const unsigned int sched_nr_migrate_break = 32;

/*
 * move_tasks tries to move up to imbalance weighted load from busiest to
 * this_rq, as part of a balancing operation within domain "sd".
 * Returns 1 if successful and 0 otherwise.
 *
 * Called with both runqueues locked.
 */
static int move_tasks(struct lb_env *env)
{
        struct list_head *tasks = &env->src_rq->cfs_tasks;
        struct task_struct *p;
        unsigned long load;
        int pulled = 0;

        if (env->imbalance <= 0)
                return 0;

        while (!list_empty(tasks)) {
                p = list_first_entry(tasks, struct task_struct, se.group_node);

                env->loop++;
                /* We've more or less seen every task there is, call it quits */
                if (env->loop > env->loop_max)
                        break;

                /* take a breather every nr_migrate tasks */
                if (env->loop > env->loop_break) {
                        env->loop_break += sched_nr_migrate_break;
                        env->flags |= LBF_NEED_BREAK;
                        break;
                }

                if (!can_migrate_task(p, env))
                        goto next;

                load = task_h_load(p);

                if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
                        goto next;

                if ((load / 2) > env->imbalance)
                        goto next;

                move_task(p, env);
                pulled++;
                env->imbalance -= load;

#ifdef CONFIG_PREEMPT
                /*
                 * NEWIDLE balancing is a source of latency, so preemptible
                 * kernels will stop after the first task is pulled to minimize
                 * the critical section.
                 */
                if (env->idle == CPU_NEWLY_IDLE)
                        break;
#endif

                /*
                 * We only want to steal up to the prescribed amount of
                 * weighted load.
                 */
                if (env->imbalance <= 0)
                        break;

                continue;
next:
                list_move_tail(&p->se.group_node, tasks);
        }

        /*
         * Right now, this is one of only two places move_task() is called,
         * so we can safely collect move_task() stats here rather than
         * inside move_task().
         */
        schedstat_add(env->sd, lb_gained[env->idle], pulled);

        return pulled;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
 * update tg->load_weight by folding this cpu's load_avg
 */
static void __update_blocked_averages_cpu(struct task_group *tg, int cpu)
{
        struct sched_entity *se = tg->se[cpu];
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu];

        /* throttled entities do not contribute to load */
        if (throttled_hierarchy(cfs_rq))
                return;

        update_cfs_rq_blocked_load(cfs_rq, 1);

        if (se) {
                update_entity_load_avg(se, 1);
                /*
                 * We pivot on our runnable average having decayed to zero for
                 * list removal.  This generally implies that all our children
                 * have also been removed (modulo rounding error or bandwidth
                 * control); however, such cases are rare and we can fix these
                 * at enqueue.
                 *
                 * TODO: fix up out-of-order children on enqueue.
                 */
                if (!se->avg.runnable_avg_sum && !cfs_rq->nr_running)
                        list_del_leaf_cfs_rq(cfs_rq);
        } else {
                struct rq *rq = rq_of(cfs_rq);
                update_rq_runnable_avg(rq, rq->nr_running);
        }
}

static void update_blocked_averages(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct cfs_rq *cfs_rq;
        unsigned long flags;

        raw_spin_lock_irqsave(&rq->lock, flags);
        update_rq_clock(rq);
        /*
         * Iterates the task_group tree in a bottom up fashion, see
         * list_add_leaf_cfs_rq() for details.
         */
        for_each_leaf_cfs_rq(rq, cfs_rq) {
                /*
                 * Note: We may want to consider periodically releasing
                 * rq->lock about these updates so that creating many task
                 * groups does not result in continually extending hold time.
                 */
                __update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
        }

        raw_spin_unlock_irqrestore(&rq->lock, flags);
}

/*
 * Compute the hierarchical load factor for cfs_rq and all its ascendants.
 * This needs to be done in a top-down fashion because the load of a child
 * group is a fraction of its parents load.
 */
static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct sched_entity *se = cfs_rq->tg->se[cpu_of(rq)];
        unsigned long now = jiffies;
        unsigned long load;

        if (cfs_rq->last_h_load_update == now)
                return;

        cfs_rq->h_load_next = NULL;
        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                cfs_rq->h_load_next = se;
                if (cfs_rq->last_h_load_update == now)
                        break;
        }

        if (!se) {
                cfs_rq->h_load = cfs_rq->runnable_load_avg;
                cfs_rq->last_h_load_update = now;
        }

        while ((se = cfs_rq->h_load_next) != NULL) {
                load = cfs_rq->h_load;
                load = div64_ul(load * se->avg.load_avg_contrib,
                                cfs_rq->runnable_load_avg + 1);
                cfs_rq = group_cfs_rq(se);
                cfs_rq->h_load = load;
                cfs_rq->last_h_load_update = now;
        }
}

static unsigned long task_h_load(struct task_struct *p)
{
        struct cfs_rq *cfs_rq = task_cfs_rq(p);

        update_cfs_rq_h_load(cfs_rq);
        return div64_ul(p->se.avg.load_avg_contrib * cfs_rq->h_load,
                        cfs_rq->runnable_load_avg + 1);
}
#else
static inline void update_blocked_averages(int cpu)
{
}

static unsigned long task_h_load(struct task_struct *p)
{
        return p->se.avg.load_avg_contrib;
}
#endif

/********** Helpers for find_busiest_group ************************/
/*
 * sg_lb_stats - stats of a sched_group required for load_balancing
 */
struct sg_lb_stats {
        unsigned long avg_load; /*Avg load across the CPUs of the group */
        unsigned long group_load; /* Total load over the CPUs of the group */
        unsigned long sum_weighted_load; /* Weighted load of group's tasks */
        unsigned long load_per_task;
        unsigned long group_capacity;
        unsigned int sum_nr_running; /* Nr tasks running in the group */
        unsigned int group_capacity_factor;
        unsigned int idle_cpus;
        unsigned int group_weight;
        int group_imb; /* Is there an imbalance in the group ? */
        int group_has_free_capacity;
#ifdef CONFIG_NUMA_BALANCING
        unsigned int nr_numa_running;
        unsigned int nr_preferred_running;
#endif
};

/*
 * sd_lb_stats - Structure to store the statistics of a sched_domain
 *               during load balancing.
 */
struct sd_lb_stats {
        struct sched_group *busiest;    /* Busiest group in this sd */
        struct sched_group *local;      /* Local group in this sd */
        unsigned long total_load;       /* Total load of all groups in sd */
        unsigned long total_capacity;   /* Total capacity of all groups in sd */
        unsigned long avg_load; /* Average load across all groups in sd */

        struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */
        struct sg_lb_stats local_stat;  /* Statistics of the local group */
};

static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
{
        /*
         * Skimp on the clearing to avoid duplicate work. We can avoid clearing
         * local_stat because update_sg_lb_stats() does a full clear/assignment.
         * We must however clear busiest_stat::avg_load because
         * update_sd_pick_busiest() reads this before assignment.
         */
        *sds = (struct sd_lb_stats){
                .busiest = NULL,
                .local = NULL,
                .total_load = 0UL,
                .total_capacity = 0UL,
                .busiest_stat = {
                        .avg_load = 0UL,
                },
        };
}

/**
 * get_sd_load_idx - Obtain the load index for a given sched domain.
 * @sd: The sched_domain whose load_idx is to be obtained.
 * @idle: The idle status of the CPU for whose sd load_idx is obtained.
 *
 * Return: The load index.
 */
static inline int get_sd_load_idx(struct sched_domain *sd,
                                        enum cpu_idle_type idle)
{
        int load_idx;

        switch (idle) {
        case CPU_NOT_IDLE:
                load_idx = sd->busy_idx;
                break;

        case CPU_NEWLY_IDLE:
                load_idx = sd->newidle_idx;
                break;
        default:
                load_idx = sd->idle_idx;
                break;
        }

        return load_idx;
}

static unsigned long default_scale_capacity(struct sched_domain *sd, int cpu)
{
        return SCHED_CAPACITY_SCALE;
}

unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
{
        return default_scale_capacity(sd, cpu);
}

static unsigned long default_scale_smt_capacity(struct sched_domain *sd, int cpu)
{
        unsigned long weight = sd->span_weight;
        unsigned long smt_gain = sd->smt_gain;

        smt_gain /= weight;

        return smt_gain;
}

unsigned long __weak arch_scale_smt_capacity(struct sched_domain *sd, int cpu)
{
        return default_scale_smt_capacity(sd, cpu);
}

static unsigned long scale_rt_capacity(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        u64 total, available, age_stamp, avg;
        s64 delta;

        /*
         * Since we're reading these variables without serialization make sure
         * we read them once before doing sanity checks on them.
         */
        age_stamp = ACCESS_ONCE(rq->age_stamp);
        avg = ACCESS_ONCE(rq->rt_avg);

        delta = rq_clock(rq) - age_stamp;
        if (unlikely(delta < 0))
                delta = 0;

        total = sched_avg_period() + delta;

        if (unlikely(total < avg)) {
                /* Ensures that capacity won't end up being negative */
                available = 0;
        } else {
                available = total - avg;
        }

        if (unlikely((s64)total < SCHED_CAPACITY_SCALE))
                total = SCHED_CAPACITY_SCALE;

        total >>= SCHED_CAPACITY_SHIFT;

        return div_u64(available, total);
}

static void update_cpu_capacity(struct sched_domain *sd, int cpu)
{
        unsigned long weight = sd->span_weight;
        unsigned long capacity = SCHED_CAPACITY_SCALE;
        struct sched_group *sdg = sd->groups;

        if ((sd->flags & SD_SHARE_CPUCAPACITY) && weight > 1) {
                if (sched_feat(ARCH_CAPACITY))
                        capacity *= arch_scale_smt_capacity(sd, cpu);
                else
                        capacity *= default_scale_smt_capacity(sd, cpu);

                capacity >>= SCHED_CAPACITY_SHIFT;
        }

        sdg->sgc->capacity_orig = capacity;

        if (sched_feat(ARCH_CAPACITY))
                capacity *= arch_scale_freq_capacity(sd, cpu);
        else
                capacity *= default_scale_capacity(sd, cpu);

        capacity >>= SCHED_CAPACITY_SHIFT;

        capacity *= scale_rt_capacity(cpu);
        capacity >>= SCHED_CAPACITY_SHIFT;

        if (!capacity)
                capacity = 1;

        cpu_rq(cpu)->cpu_capacity = capacity;
        sdg->sgc->capacity = capacity;
}

void update_group_capacity(struct sched_domain *sd, int cpu)
{
        struct sched_domain *child = sd->child;
        struct sched_group *group, *sdg = sd->groups;
        unsigned long capacity, capacity_orig;
        unsigned long interval;

        interval = msecs_to_jiffies(sd->balance_interval);
        interval = clamp(interval, 1UL, max_load_balance_interval);
        sdg->sgc->next_update = jiffies + interval;

        if (!child) {
                update_cpu_capacity(sd, cpu);
                return;
        }

        capacity_orig = capacity = 0;

        if (child->flags & SD_OVERLAP) {
                /*
                 * SD_OVERLAP domains cannot assume that child groups
                 * span the current group.
                 */

                for_each_cpu(cpu, sched_group_cpus(sdg)) {
                        struct sched_group_capacity *sgc;
                        struct rq *rq = cpu_rq(cpu);

                        /*
                         * build_sched_domains() -> init_sched_groups_capacity()
                         * gets here before we've attached the domains to the
                         * runqueues.
                         *
                         * Use capacity_of(), which is set irrespective of domains
                         * in update_cpu_capacity().
                         *
                         * This avoids capacity/capacity_orig from being 0 and
                         * causing divide-by-zero issues on boot.
                         *
                         * Runtime updates will correct capacity_orig.
                         */
                        if (unlikely(!rq->sd)) {
                                capacity_orig += capacity_of(cpu);
                                capacity += capacity_of(cpu);
                                continue;
                        }

                        sgc = rq->sd->groups->sgc;
                        capacity_orig += sgc->capacity_orig;
                        capacity += sgc->capacity;
                }
        } else  {
                /*
                 * !SD_OVERLAP domains can assume that child groups
                 * span the current group.
                 */ 

                group = child->groups;
                do {
                        capacity_orig += group->sgc->capacity_orig;
                        capacity += group->sgc->capacity;
                        group = group->next;
                } while (group != child->groups);
        }

        sdg->sgc->capacity_orig = capacity_orig;
        sdg->sgc->capacity = capacity;
}

/*
 * Try and fix up capacity for tiny siblings, this is needed when
 * things like SD_ASYM_PACKING need f_b_g to select another sibling
 * which on its own isn't powerful enough.
 *
 * See update_sd_pick_busiest() and check_asym_packing().
 */
static inline int
fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
{
        /*
         * Only siblings can have significantly less than SCHED_CAPACITY_SCALE
         */
        if (!(sd->flags & SD_SHARE_CPUCAPACITY))
                return 0;

        /*
         * If ~90% of the cpu_capacity is still there, we're good.
         */
        if (group->sgc->capacity * 32 > group->sgc->capacity_orig * 29)
                return 1;

        return 0;
}

/*
 * Group imbalance indicates (and tries to solve) the problem where balancing
 * groups is inadequate due to tsk_cpus_allowed() constraints.
 *
 * Imagine a situation of two groups of 4 cpus each and 4 tasks each with a
 * cpumask covering 1 cpu of the first group and 3 cpus of the second group.
 * Something like:
 *
 *      { 0 1 2 3 } { 4 5 6 7 }
 *              *     * * *
 *
 * If we were to balance group-wise we'd place two tasks in the first group and
 * two tasks in the second group. Clearly this is undesired as it will overload
 * cpu 3 and leave one of the cpus in the second group unused.
 *
 * The current solution to this issue is detecting the skew in the first group
 * by noticing the lower domain failed to reach balance and had difficulty
 * moving tasks due to affinity constraints.
 *
 * When this is so detected; this group becomes a candidate for busiest; see
 * update_sd_pick_busiest(). And calculate_imbalance() and
 * find_busiest_group() avoid some of the usual balance conditions to allow it
 * to create an effective group imbalance.
 *
 * This is a somewhat tricky proposition since the next run might not find the
 * group imbalance and decide the groups need to be balanced again. A most
 * subtle and fragile situation.
 */

static inline int sg_imbalanced(struct sched_group *group)
{
        return group->sgc->imbalance;
}

/*
 * Compute the group capacity factor.
 *
 * Avoid the issue where N*frac(smt_capacity) >= 1 creates 'phantom' cores by
 * first dividing out the smt factor and computing the actual number of cores
 * and limit unit capacity with that.
 */
static inline int sg_capacity_factor(struct lb_env *env, struct sched_group *group)
{
        unsigned int capacity_factor, smt, cpus;
        unsigned int capacity, capacity_orig;

        capacity = group->sgc->capacity;
        capacity_orig = group->sgc->capacity_orig;
        cpus = group->group_weight;

        /* smt := ceil(cpus / capacity), assumes: 1 < smt_capacity < 2 */
        smt = DIV_ROUND_UP(SCHED_CAPACITY_SCALE * cpus, capacity_orig);
        capacity_factor = cpus / smt; /* cores */

        capacity_factor = min_t(unsigned,
                capacity_factor, DIV_ROUND_CLOSEST(capacity, SCHED_CAPACITY_SCALE));
        if (!capacity_factor)
                capacity_factor = fix_small_capacity(env->sd, group);

        return capacity_factor;
}

/**
 * update_sg_lb_stats - Update sched_group's statistics for load balancing.
 * @env: The load balancing environment.
 * @group: sched_group whose statistics are to be updated.
 * @load_idx: Load index of sched_domain of this_cpu for load calc.
 * @local_group: Does group contain this_cpu.
 * @sgs: variable to hold the statistics for this group.
 */
static inline void update_sg_lb_stats(struct lb_env *env,
                        struct sched_group *group, int load_idx,
                        int local_group, struct sg_lb_stats *sgs,
                        bool *overload)
{
        unsigned long load;
        int i;

        memset(sgs, 0, sizeof(*sgs));

        for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
                struct rq *rq = cpu_rq(i);

                /* Bias balancing toward cpus of our domain */
                if (local_group)
                        load = target_load(i, load_idx);
                else
                        load = source_load(i, load_idx);

                sgs->group_load += load;
                sgs->sum_nr_running += rq->nr_running;

                if (rq->nr_running > 1)
                        *overload = true;

#ifdef CONFIG_NUMA_BALANCING
                sgs->nr_numa_running += rq->nr_numa_running;
                sgs->nr_preferred_running += rq->nr_preferred_running;
#endif
                sgs->sum_weighted_load += weighted_cpuload(i);
                if (idle_cpu(i))
                        sgs->idle_cpus++;
        }

        /* Adjust by relative CPU capacity of the group */
        sgs->group_capacity = group->sgc->capacity;
        sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity;

        if (sgs->sum_nr_running)
                sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;

        sgs->group_weight = group->group_weight;

        sgs->group_imb = sg_imbalanced(group);
        sgs->group_capacity_factor = sg_capacity_factor(env, group);

        if (sgs->group_capacity_factor > sgs->sum_nr_running)
                sgs->group_has_free_capacity = 1;
}

/**
 * update_sd_pick_busiest - return 1 on busiest group
 * @env: The load balancing environment.
 * @sds: sched_domain statistics
 * @sg: sched_group candidate to be checked for being the busiest
 * @sgs: sched_group statistics
 *
 * Determine if @sg is a busier group than the previously selected
 * busiest group.
 *
 * Return: %true if @sg is a busier group than the previously selected
 * busiest group. %false otherwise.
 */
static bool update_sd_pick_busiest(struct lb_env *env,
                                   struct sd_lb_stats *sds,
                                   struct sched_group *sg,
                                   struct sg_lb_stats *sgs)
{
        if (sgs->avg_load <= sds->busiest_stat.avg_load)
                return false;

        if (sgs->sum_nr_running > sgs->group_capacity_factor)
                return true;

        if (sgs->group_imb)
                return true;

        /*
         * ASYM_PACKING needs to move all the work to the lowest
         * numbered CPUs in the group, therefore mark all groups
         * higher than ourself as busy.
         */
        if ((env->sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running &&
            env->dst_cpu < group_first_cpu(sg)) {
                if (!sds->busiest)
                        return true;

                if (group_first_cpu(sds->busiest) > group_first_cpu(sg))
                        return true;
        }

        return false;
}

#ifdef CONFIG_NUMA_BALANCING
static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
{
        if (sgs->sum_nr_running > sgs->nr_numa_running)
                return regular;
        if (sgs->sum_nr_running > sgs->nr_preferred_running)
                return remote;
        return all;
}

static inline enum fbq_type fbq_classify_rq(struct rq *rq)
{
        if (rq->nr_running > rq->nr_numa_running)
                return regular;
        if (rq->nr_running > rq->nr_preferred_running)
                return remote;
        return all;
}
#else
static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
{
        return all;
}

static inline enum fbq_type fbq_classify_rq(struct rq *rq)
{
        return regular;
}
#endif /* CONFIG_NUMA_BALANCING */

/**
 * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
 * @env: The load balancing environment.
 * @sds: variable to hold the statistics for this sched_domain.
 */
static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
{
        struct sched_domain *child = env->sd->child;
        struct sched_group *sg = env->sd->groups;
        struct sg_lb_stats tmp_sgs;
        int load_idx, prefer_sibling = 0;
        bool overload = false;

        if (child && child->flags & SD_PREFER_SIBLING)
                prefer_sibling = 1;

        load_idx = get_sd_load_idx(env->sd, env->idle);

        do {
                struct sg_lb_stats *sgs = &tmp_sgs;
                int local_group;

                local_group = cpumask_test_cpu(env->dst_cpu, sched_group_cpus(sg));
                if (local_group) {
                        sds->local = sg;
                        sgs = &sds->local_stat;

                        if (env->idle != CPU_NEWLY_IDLE ||
                            time_after_eq(jiffies, sg->sgc->next_update))
                                update_group_capacity(env->sd, env->dst_cpu);
                }

                update_sg_lb_stats(env, sg, load_idx, local_group, sgs,
                                                &overload);

                if (local_group)
                        goto next_group;

                /*
                 * In case the child domain prefers tasks go to siblings
                 * first, lower the sg capacity factor to one so that we'll try
                 * and move all the excess tasks away. We lower the capacity
                 * of a group only if the local group has the capacity to fit
                 * these excess tasks, i.e. nr_running < group_capacity_factor. The
                 * extra check prevents the case where you always pull from the
                 * heaviest group when it is already under-utilized (possible
                 * with a large weight task outweighs the tasks on the system).
                 */
                if (prefer_sibling && sds->local &&
                    sds->local_stat.group_has_free_capacity)
                        sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);

                if (update_sd_pick_busiest(env, sds, sg, sgs)) {
                        sds->busiest = sg;
                        sds->busiest_stat = *sgs;
                }

next_group:
                /* Now, start updating sd_lb_stats */
                sds->total_load += sgs->group_load;
                sds->total_capacity += sgs->group_capacity;

                sg = sg->next;
        } while (sg != env->sd->groups);

        if (env->sd->flags & SD_NUMA)
                env->fbq_type = fbq_classify_group(&sds->busiest_stat);

        if (!env->sd->parent) {
                /* update overload indicator if we are at root domain */
                if (env->dst_rq->rd->overload != overload)
                        env->dst_rq->rd->overload = overload;
        }

}

/**
 * check_asym_packing - Check to see if the group is packed into the
 *                      sched doman.
 *
 * This is primarily intended to used at the sibling level.  Some
 * cores like POWER7 prefer to use lower numbered SMT threads.  In the
 * case of POWER7, it can move to lower SMT modes only when higher
 * threads are idle.  When in lower SMT modes, the threads will
 * perform better since they share less core resources.  Hence when we
 * have idle threads, we want them to be the higher ones.
 *
 * This packing function is run on idle threads.  It checks to see if
 * the busiest CPU in this domain (core in the P7 case) has a higher
 * CPU number than the packing function is being run on.  Here we are
 * assuming lower CPU number will be equivalent to lower a SMT thread
 * number.
 *
 * Return: 1 when packing is required and a task should be moved to
 * this CPU.  The amount of the imbalance is returned in *imbalance.
 *
 * @env: The load balancing environment.
 * @sds: Statistics of the sched_domain which is to be packed
 */
static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
{
        int busiest_cpu;

        if (!(env->sd->flags & SD_ASYM_PACKING))
                return 0;

        if (!sds->busiest)
                return 0;

        busiest_cpu = group_first_cpu(sds->busiest);
        if (env->dst_cpu > busiest_cpu)
                return 0;

        env->imbalance = DIV_ROUND_CLOSEST(
                sds->busiest_stat.avg_load * sds->busiest_stat.group_capacity,
                SCHED_CAPACITY_SCALE);

        return 1;
}

/**
 * fix_small_imbalance - Calculate the minor imbalance that exists
 *                      amongst the groups of a sched_domain, during
 *                      load balancing.
 * @env: The load balancing environment.
 * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
 */
static inline
void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
{
        unsigned long tmp, capa_now = 0, capa_move = 0;
        unsigned int imbn = 2;
        unsigned long scaled_busy_load_per_task;
        struct sg_lb_stats *local, *busiest;

        local = &sds->local_stat;
        busiest = &sds->busiest_stat;

        if (!local->sum_nr_running)
                local->load_per_task = cpu_avg_load_per_task(env->dst_cpu);
        else if (busiest->load_per_task > local->load_per_task)
                imbn = 1;

        scaled_busy_load_per_task =
                (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
                busiest->group_capacity;

        if (busiest->avg_load + scaled_busy_load_per_task >=
            local->avg_load + (scaled_busy_load_per_task * imbn)) {
                env->imbalance = busiest->load_per_task;
                return;
        }

        /*
         * OK, we don't have enough imbalance to justify moving tasks,
         * however we may be able to increase total CPU capacity used by
         * moving them.
         */

        capa_now += busiest->group_capacity *
                        min(busiest->load_per_task, busiest->avg_load);
        capa_now += local->group_capacity *
                        min(local->load_per_task, local->avg_load);
        capa_now /= SCHED_CAPACITY_SCALE;

        /* Amount of load we'd subtract */
        if (busiest->avg_load > scaled_busy_load_per_task) {
                capa_move += busiest->group_capacity *
                            min(busiest->load_per_task,
                                busiest->avg_load - scaled_busy_load_per_task);
        }

        /* Amount of load we'd add */
        if (busiest->avg_load * busiest->group_capacity <
            busiest->load_per_task * SCHED_CAPACITY_SCALE) {
                tmp = (busiest->avg_load * busiest->group_capacity) /
                      local->group_capacity;
        } else {
                tmp = (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
                      local->group_capacity;
        }
        capa_move += local->group_capacity *
                    min(local->load_per_task, local->avg_load + tmp);
        capa_move /= SCHED_CAPACITY_SCALE;

        /* Move if we gain throughput */
        if (capa_move > capa_now)
                env->imbalance = busiest->load_per_task;
}

/**
 * calculate_imbalance - Calculate the amount of imbalance present within the
 *                       groups of a given sched_domain during load balance.
 * @env: load balance environment
 * @sds: statistics of the sched_domain whose imbalance is to be calculated.
 */
static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
{
        unsigned long max_pull, load_above_capacity = ~0UL;
        struct sg_lb_stats *local, *busiest;

        local = &sds->local_stat;
        busiest = &sds->busiest_stat;

        if (busiest->group_imb) {
                /*
                 * In the group_imb case we cannot rely on group-wide averages
                 * to ensure cpu-load equilibrium, look at wider averages. XXX
                 */
                busiest->load_per_task =
                        min(busiest->load_per_task, sds->avg_load);
        }

        /*
         * In the presence of smp nice balancing, certain scenarios can have
         * max load less than avg load(as we skip the groups at or below
         * its cpu_capacity, while calculating max_load..)
         */
        if (busiest->avg_load <= sds->avg_load ||
            local->avg_load >= sds->avg_load) {
                env->imbalance = 0;
                return fix_small_imbalance(env, sds);
        }

        if (!busiest->group_imb) {
                /*
                 * Don't want to pull so many tasks that a group would go idle.
                 * Except of course for the group_imb case, since then we might
                 * have to drop below capacity to reach cpu-load equilibrium.
                 */
                load_above_capacity =
                        (busiest->sum_nr_running - busiest->group_capacity_factor);

                load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_CAPACITY_SCALE);
                load_above_capacity /= busiest->group_capacity;
        }

        /*
         * We're trying to get all the cpus to the average_load, so we don't
         * want to push ourselves above the average load, nor do we wish to
         * reduce the max loaded cpu below the average load. At the same time,
         * we also don't want to reduce the group load below the group capacity
         * (so that we can implement power-savings policies etc). Thus we look
         * for the minimum possible imbalance.
         */
        max_pull = min(busiest->avg_load - sds->avg_load, load_above_capacity);

        /* How much load to actually move to equalise the imbalance */
        env->imbalance = min(
                max_pull * busiest->group_capacity,
                (sds->avg_load - local->avg_load) * local->group_capacity
        ) / SCHED_CAPACITY_SCALE;

        /*
         * if *imbalance is less than the average load per runnable task
         * there is no guarantee that any tasks will be moved so we'll have
         * a think about bumping its value to force at least one task to be
         * moved
         */
        if (env->imbalance < busiest->load_per_task)
                return fix_small_imbalance(env, sds);
}

/******* find_busiest_group() helpers end here *********************/

/**
 * find_busiest_group - Returns the busiest group within the sched_domain
 * if there is an imbalance. If there isn't an imbalance, and
 * the user has opted for power-savings, it returns a group whose
 * CPUs can be put to idle by rebalancing those tasks elsewhere, if
 * such a group exists.
 *
 * Also calculates the amount of weighted load which should be moved
 * to restore balance.
 *
 * @env: The load balancing environment.
 *
 * Return:      - The busiest group if imbalance exists.
 *              - If no imbalance and user has opted for power-savings balance,
 *                 return the least loaded group whose CPUs can be
 *                 put to idle by rebalancing its tasks onto our group.
 */
static struct sched_group *find_busiest_group(struct lb_env *env)
{
        struct sg_lb_stats *local, *busiest;
        struct sd_lb_stats sds;

        init_sd_lb_stats(&sds);

        /*
         * Compute the various statistics relavent for load balancing at
         * this level.
         */
        update_sd_lb_stats(env, &sds);
        local = &sds.local_stat;
        busiest = &sds.busiest_stat;

        if ((env->idle == CPU_IDLE || env->idle == CPU_NEWLY_IDLE) &&
            check_asym_packing(env, &sds))
                return sds.busiest;

        /* There is no busy sibling group to pull tasks from */
        if (!sds.busiest || busiest->sum_nr_running == 0)
                goto out_balanced;

        sds.avg_load = (SCHED_CAPACITY_SCALE * sds.total_load)
                                                / sds.total_capacity;

        /*
         * If the busiest group is imbalanced the below checks don't
         * work because they assume all things are equal, which typically
         * isn't true due to cpus_allowed constraints and the like.
         */
        if (busiest->group_imb)
                goto force_balance;

        /* SD_BALANCE_NEWIDLE trumps SMP nice when underutilized */
        if (env->idle == CPU_NEWLY_IDLE && local->group_has_free_capacity &&
            !busiest->group_has_free_capacity)
                goto force_balance;

        /*
         * If the local group is more busy than the selected busiest group
         * don't try and pull any tasks.
         */
        if (local->avg_load >= busiest->avg_load)
                goto out_balanced;

        /*
         * Don't pull any tasks if this group is already above the domain
         * average load.
         */
        if (local->avg_load >= sds.avg_load)
                goto out_balanced;

        if (env->idle == CPU_IDLE) {
                /*
                 * This cpu is idle. If the busiest group load doesn't
                 * have more tasks than the number of available cpu's and
                 * there is no imbalance between this and busiest group
                 * wrt to idle cpu's, it is balanced.
                 */
                if ((local->idle_cpus < busiest->idle_cpus) &&
                    busiest->sum_nr_running <= busiest->group_weight)
                        goto out_balanced;
        } else {
                /*
                 * In the CPU_NEWLY_IDLE, CPU_NOT_IDLE cases, use
                 * imbalance_pct to be conservative.
                 */
                if (100 * busiest->avg_load <=
                                env->sd->imbalance_pct * local->avg_load)
                        goto out_balanced;
        }

force_balance:
        /* Looks like there is an imbalance. Compute it */
        calculate_imbalance(env, &sds);
        return sds.busiest;

out_balanced:
        env->imbalance = 0;
        return NULL;
}

/*
 * find_busiest_queue - find the busiest runqueue among the cpus in group.
 */
static struct rq *find_busiest_queue(struct lb_env *env,
                                     struct sched_group *group)
{
        struct rq *busiest = NULL, *rq;
        unsigned long busiest_load = 0, busiest_capacity = 1;
        int i;

        for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
                unsigned long capacity, capacity_factor, wl;
                enum fbq_type rt;

                rq = cpu_rq(i);
                rt = fbq_classify_rq(rq);

                /*
                 * We classify groups/runqueues into three groups:
                 *  - regular: there are !numa tasks
                 *  - remote:  there are numa tasks that run on the 'wrong' node
                 *  - all:     there is no distinction
                 *
                 * In order to avoid migrating ideally placed numa tasks,
                 * ignore those when there's better options.
                 *
                 * If we ignore the actual busiest queue to migrate another
                 * task, the next balance pass can still reduce the busiest
                 * queue by moving tasks around inside the node.
                 *
                 * If we cannot move enough load due to this classification
                 * the next pass will adjust the group classification and
                 * allow migration of more tasks.
                 *
                 * Both cases only affect the total convergence complexity.
                 */
                if (rt > env->fbq_type)
                        continue;

                capacity = capacity_of(i);
                capacity_factor = DIV_ROUND_CLOSEST(capacity, SCHED_CAPACITY_SCALE);
                if (!capacity_factor)
                        capacity_factor = fix_small_capacity(env->sd, group);

                wl = weighted_cpuload(i);

                /*
                 * When comparing with imbalance, use weighted_cpuload()
                 * which is not scaled with the cpu capacity.
                 */
                if (capacity_factor && rq->nr_running == 1 && wl > env->imbalance)
                        continue;

                /*
                 * For the load comparisons with the other cpu's, consider
                 * the weighted_cpuload() scaled with the cpu capacity, so
                 * that the load can be moved away from the cpu that is
                 * potentially running at a lower capacity.
                 *
                 * Thus we're looking for max(wl_i / capacity_i), crosswise
                 * multiplication to rid ourselves of the division works out
                 * to: wl_i * capacity_j > wl_j * capacity_i;  where j is
                 * our previous maximum.
                 */
                if (wl * busiest_capacity > busiest_load * capacity) {
                        busiest_load = wl;
                        busiest_capacity = capacity;
                        busiest = rq;
                }
        }

        return busiest;
}

/*
 * Max backoff if we encounter pinned tasks. Pretty arbitrary value, but
 * so long as it is large enough.
 */
#define MAX_PINNED_INTERVAL     512

/* Working cpumask for load_balance and load_balance_newidle. */
DEFINE_PER_CPU(cpumask_var_t, load_balance_mask);

static int need_active_balance(struct lb_env *env)
{
        struct sched_domain *sd = env->sd;

        if (env->idle == CPU_NEWLY_IDLE) {

                /*
                 * ASYM_PACKING needs to force migrate tasks from busy but
                 * higher numbered CPUs in order to pack all tasks in the
                 * lowest numbered CPUs.
                 */
                if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu)
                        return 1;
        }

        return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}

static int active_load_balance_cpu_stop(void *data);

static int should_we_balance(struct lb_env *env)
{
        struct sched_group *sg = env->sd->groups;
        struct cpumask *sg_cpus, *sg_mask;
        int cpu, balance_cpu = -1;

        /*
         * In the newly idle case, we will allow all the cpu's
         * to do the newly idle load balance.
         */
        if (env->idle == CPU_NEWLY_IDLE)
                return 1;

        sg_cpus = sched_group_cpus(sg);
        sg_mask = sched_group_mask(sg);
        /* Try to find first idle cpu */
        for_each_cpu_and(cpu, sg_cpus, env->cpus) {
                if (!cpumask_test_cpu(cpu, sg_mask) || !idle_cpu(cpu))
                        continue;

                balance_cpu = cpu;
                break;
        }

        if (balance_cpu == -1)
                balance_cpu = group_balance_cpu(sg);

        /*
         * First idle cpu or the first cpu(busiest) in this sched group
         * is eligible for doing load balancing at this and above domains.
         */
        return balance_cpu == env->dst_cpu;
}

/*
 * Check this_cpu to ensure it is balanced within domain. Attempt to move
 * tasks if there is an imbalance.
 */
static int load_balance(int this_cpu, struct rq *this_rq,
                        struct sched_domain *sd, enum cpu_idle_type idle,
                        int *continue_balancing)
{
        int ld_moved, cur_ld_moved, active_balance = 0;
        struct sched_domain *sd_parent = sd->parent;
        struct sched_group *group;
        struct rq *busiest;
        unsigned long flags;
        struct cpumask *cpus = __get_cpu_var(load_balance_mask);

        struct lb_env env = {
                .sd             = sd,
                .dst_cpu        = this_cpu,
                .dst_rq         = this_rq,
                .dst_grpmask    = sched_group_cpus(sd->groups),
                .idle           = idle,
                .loop_break     = sched_nr_migrate_break,
                .cpus           = cpus,
                .fbq_type       = all,
        };

        /*
         * For NEWLY_IDLE load_balancing, we don't need to consider
         * other cpus in our group
         */
        if (idle == CPU_NEWLY_IDLE)
                env.dst_grpmask = NULL;

        cpumask_copy(cpus, cpu_active_mask);

        schedstat_inc(sd, lb_count[idle]);

redo:
        if (!should_we_balance(&env)) {
                *continue_balancing = 0;
                goto out_balanced;
        }

        group = find_busiest_group(&env);
        if (!group) {
                schedstat_inc(sd, lb_nobusyg[idle]);
                goto out_balanced;
        }

        busiest = find_busiest_queue(&env, group);
        if (!busiest) {
                schedstat_inc(sd, lb_nobusyq[idle]);
                goto out_balanced;
        }

        BUG_ON(busiest == env.dst_rq);

        schedstat_add(sd, lb_imbalance[idle], env.imbalance);

        ld_moved = 0;
        if (busiest->nr_running > 1) {
                /*
                 * Attempt to move tasks. If find_busiest_group has found
                 * an imbalance but busiest->nr_running <= 1, the group is
                 * still unbalanced. ld_moved simply stays zero, so it is
                 * correctly treated as an imbalance.
                 */
                env.flags |= LBF_ALL_PINNED;
                env.src_cpu   = busiest->cpu;
                env.src_rq    = busiest;
                env.loop_max  = min(sysctl_sched_nr_migrate, busiest->nr_running);

more_balance:
                local_irq_save(flags);
                double_rq_lock(env.dst_rq, busiest);

                /*
                 * cur_ld_moved - load moved in current iteration
                 * ld_moved     - cumulative load moved across iterations
                 */
                cur_ld_moved = move_tasks(&env);
                ld_moved += cur_ld_moved;
                double_rq_unlock(env.dst_rq, busiest);
                local_irq_restore(flags);

                /*
                 * some other cpu did the load balance for us.
                 */
                if (cur_ld_moved && env.dst_cpu != smp_processor_id())
                        resched_cpu(env.dst_cpu);

                if (env.flags & LBF_NEED_BREAK) {
                        env.flags &= ~LBF_NEED_BREAK;
                        goto more_balance;
                }

                /*
                 * Revisit (affine) tasks on src_cpu that couldn't be moved to
                 * us and move them to an alternate dst_cpu in our sched_group
                 * where they can run. The upper limit on how many times we
                 * iterate on same src_cpu is dependent on number of cpus in our
                 * sched_group.
                 *
                 * This changes load balance semantics a bit on who can move
                 * load to a given_cpu. In addition to the given_cpu itself
                 * (or a ilb_cpu acting on its behalf where given_cpu is
                 * nohz-idle), we now have balance_cpu in a position to move
                 * load to given_cpu. In rare situations, this may cause
                 * conflicts (balance_cpu and given_cpu/ilb_cpu deciding
                 * _independently_ and at _same_ time to move some load to
                 * given_cpu) causing exceess load to be moved to given_cpu.
                 * This however should not happen so much in practice and
                 * moreover subsequent load balance cycles should correct the
                 * excess load moved.
                 */
                if ((env.flags & LBF_DST_PINNED) && env.imbalance > 0) {

                        /* Prevent to re-select dst_cpu via env's cpus */
                        cpumask_clear_cpu(env.dst_cpu, env.cpus);

                        env.dst_rq       = cpu_rq(env.new_dst_cpu);
                        env.dst_cpu      = env.new_dst_cpu;
                        env.flags       &= ~LBF_DST_PINNED;
                        env.loop         = 0;
                        env.loop_break   = sched_nr_migrate_break;

                        /*
                         * Go back to "more_balance" rather than "redo" since we
                         * need to continue with same src_cpu.
                         */
                        goto more_balance;
                }

                /*
                 * We failed to reach balance because of affinity.
                 */
                if (sd_parent) {
                        int *group_imbalance = &sd_parent->groups->sgc->imbalance;

                        if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0) {
                                *group_imbalance = 1;
                        } else if (*group_imbalance)
                                *group_imbalance = 0;
                }

                /* All tasks on this runqueue were pinned by CPU affinity */
                if (unlikely(env.flags & LBF_ALL_PINNED)) {
                        cpumask_clear_cpu(cpu_of(busiest), cpus);
                        if (!cpumask_empty(cpus)) {
                                env.loop = 0;
                                env.loop_break = sched_nr_migrate_break;
                                goto redo;
                        }
                        goto out_balanced;
                }
        }

        if (!ld_moved) {
                schedstat_inc(sd, lb_failed[idle]);
                /*
                 * Increment the failure counter only on periodic balance.
                 * We do not want newidle balance, which can be very
                 * frequent, pollute the failure counter causing
                 * excessive cache_hot migrations and active balances.
                 */
                if (idle != CPU_NEWLY_IDLE)
                        sd->nr_balance_failed++;

                if (need_active_balance(&env)) {
                        raw_spin_lock_irqsave(&busiest->lock, flags);

                        /* don't kick the active_load_balance_cpu_stop,
                         * if the curr task on busiest cpu can't be
                         * moved to this_cpu
                         */
                        if (!cpumask_test_cpu(this_cpu,
                                        tsk_cpus_allowed(busiest->curr))) {
                                raw_spin_unlock_irqrestore(&busiest->lock,
                                                            flags);
                                env.flags |= LBF_ALL_PINNED;
                                goto out_one_pinned;
                        }

                        /*
                         * ->active_balance synchronizes accesses to
                         * ->active_balance_work.  Once set, it's cleared
                         * only after active load balance is finished.
                         */
                        if (!busiest->active_balance) {
                                busiest->active_balance = 1;
                                busiest->push_cpu = this_cpu;
                                active_balance = 1;
                        }
                        raw_spin_unlock_irqrestore(&busiest->lock, flags);

                        if (active_balance) {
                                stop_one_cpu_nowait(cpu_of(busiest),
                                        active_load_balance_cpu_stop, busiest,
                                        &busiest->active_balance_work);
                        }

                        /*
                         * We've kicked active balancing, reset the failure
                         * counter.
                         */
                        sd->nr_balance_failed = sd->cache_nice_tries+1;
                }
        } else
                sd->nr_balance_failed = 0;

        if (likely(!active_balance)) {
                /* We were unbalanced, so reset the balancing interval */
                sd->balance_interval = sd->min_interval;
        } else {
                /*
                 * If we've begun active balancing, start to back off. This
                 * case may not be covered by the all_pinned logic if there
                 * is only 1 task on the busy runqueue (because we don't call
                 * move_tasks).
                 */
                if (sd->balance_interval < sd->max_interval)
                        sd->balance_interval *= 2;
        }

        goto out;

out_balanced:
        schedstat_inc(sd, lb_balanced[idle]);

        sd->nr_balance_failed = 0;

out_one_pinned:
        /* tune up the balancing interval */
        if (((env.flags & LBF_ALL_PINNED) &&
                        sd->balance_interval < MAX_PINNED_INTERVAL) ||
                        (sd->balance_interval < sd->max_interval))
                sd->balance_interval *= 2;

        ld_moved = 0;
out:
        return ld_moved;
}

static inline unsigned long
get_sd_balance_interval(struct sched_domain *sd, int cpu_busy)
{
        unsigned long interval = sd->balance_interval;

        if (cpu_busy)
                interval *= sd->busy_factor;

        /* scale ms to jiffies */
        interval = msecs_to_jiffies(interval);
        interval = clamp(interval, 1UL, max_load_balance_interval);

        return interval;
}

static inline void
update_next_balance(struct sched_domain *sd, int cpu_busy, unsigned long *next_balance)
{
        unsigned long interval, next;

        interval = get_sd_balance_interval(sd, cpu_busy);
        next = sd->last_balance + interval;

        if (time_after(*next_balance, next))
                *next_balance = next;
}

/*
 * idle_balance is called by schedule() if this_cpu is about to become
 * idle. Attempts to pull tasks from other CPUs.
 */
static int idle_balance(struct rq *this_rq)
{
        unsigned long next_balance = jiffies + HZ;
        int this_cpu = this_rq->cpu;
        struct sched_domain *sd;
        int pulled_task = 0;
        u64 curr_cost = 0;

        idle_enter_fair(this_rq);

        /*
         * We must set idle_stamp _before_ calling idle_balance(), such that we
         * measure the duration of idle_balance() as idle time.
         */
        this_rq->idle_stamp = rq_clock(this_rq);

        if (this_rq->avg_idle < sysctl_sched_migration_cost ||
            !this_rq->rd->overload) {
                rcu_read_lock();
                sd = rcu_dereference_check_sched_domain(this_rq->sd);
                if (sd)
                        update_next_balance(sd, 0, &next_balance);
                rcu_read_unlock();

                goto out;
        }

        /*
         * Drop the rq->lock, but keep IRQ/preempt disabled.
         */
        raw_spin_unlock(&this_rq->lock);

        update_blocked_averages(this_cpu);
        rcu_read_lock();
        for_each_domain(this_cpu, sd) {
                int continue_balancing = 1;
                u64 t0, domain_cost;

                if (!(sd->flags & SD_LOAD_BALANCE))
                        continue;

                if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) {
                        update_next_balance(sd, 0, &next_balance);
                        break;
                }

                if (sd->flags & SD_BALANCE_NEWIDLE) {
                        t0 = sched_clock_cpu(this_cpu);

                        pulled_task = load_balance(this_cpu, this_rq,
                                                   sd, CPU_NEWLY_IDLE,
                                                   &continue_balancing);

                        domain_cost = sched_clock_cpu(this_cpu) - t0;
                        if (domain_cost > sd->max_newidle_lb_cost)
                                sd->max_newidle_lb_cost = domain_cost;

                        curr_cost += domain_cost;
                }

                update_next_balance(sd, 0, &next_balance);

                /*
                 * Stop searching for tasks to pull if there are
                 * now runnable tasks on this rq.
                 */
                if (pulled_task || this_rq->nr_running > 0)
                        break;
        }
        rcu_read_unlock();

        raw_spin_lock(&this_rq->lock);

        if (curr_cost > this_rq->max_idle_balance_cost)
                this_rq->max_idle_balance_cost = curr_cost;

        /*
         * While browsing the domains, we released the rq lock, a task could
         * have been enqueued in the meantime. Since we're not going idle,
         * pretend we pulled a task.
         */
        if (this_rq->cfs.h_nr_running && !pulled_task)
                pulled_task = 1;

out:
        /* Move the next balance forward */
        if (time_after(this_rq->next_balance, next_balance))
                this_rq->next_balance = next_balance;

        /* Is there a task of a high priority class? */
        if (this_rq->nr_running != this_rq->cfs.h_nr_running)
                pulled_task = -1;

        if (pulled_task) {
                idle_exit_fair(this_rq);
                this_rq->idle_stamp = 0;
        }

        return pulled_task;
}

/*
 * active_load_balance_cpu_stop is run by cpu stopper. It pushes
 * running tasks off the busiest CPU onto idle CPUs. It requires at
 * least 1 task to be running on each physical CPU where possible, and
 * avoids physical / logical imbalances.
 */
static int active_load_balance_cpu_stop(void *data)
{
        struct rq *busiest_rq = data;
        int busiest_cpu = cpu_of(busiest_rq);
        int target_cpu = busiest_rq->push_cpu;
        struct rq *target_rq = cpu_rq(target_cpu);
        struct sched_domain *sd;

        raw_spin_lock_irq(&busiest_rq->lock);

        /* make sure the requested cpu hasn't gone down in the meantime */
        if (unlikely(busiest_cpu != smp_processor_id() ||
                     !busiest_rq->active_balance))
                goto out_unlock;

        /* Is there any task to move? */
        if (busiest_rq->nr_running <= 1)
                goto out_unlock;

        /*
         * This condition is "impossible", if it occurs
         * we need to fix it. Originally reported by
         * Bjorn Helgaas on a 128-cpu setup.
         */
        BUG_ON(busiest_rq == target_rq);

        /* move a task from busiest_rq to target_rq */
        double_lock_balance(busiest_rq, target_rq);

        /* Search for an sd spanning us and the target CPU. */
        rcu_read_lock();
        for_each_domain(target_cpu, sd) {
                if ((sd->flags & SD_LOAD_BALANCE) &&
                    cpumask_test_cpu(busiest_cpu, sched_domain_span(sd)))
                                break;
        }

        if (likely(sd)) {
                struct lb_env env = {
                        .sd             = sd,
                        .dst_cpu        = target_cpu,
                        .dst_rq         = target_rq,
                        .src_cpu        = busiest_rq->cpu,
                        .src_rq         = busiest_rq,
                        .idle           = CPU_IDLE,
                };

                schedstat_inc(sd, alb_count);

                if (move_one_task(&env))
                        schedstat_inc(sd, alb_pushed);
                else
                        schedstat_inc(sd, alb_failed);
        }
        rcu_read_unlock();
        double_unlock_balance(busiest_rq, target_rq);
out_unlock:
        busiest_rq->active_balance = 0;
        raw_spin_unlock_irq(&busiest_rq->lock);
        return 0;
}

static inline int on_null_domain(struct rq *rq)
{
        return unlikely(!rcu_dereference_sched(rq->sd));
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * idle load balancing details
 * - When one of the busy CPUs notice that there may be an idle rebalancing
 *   needed, they will kick the idle load balancer, which then does idle
 *   load balancing for all the idle CPUs.
 */
static struct {
        cpumask_var_t idle_cpus_mask;
        atomic_t nr_cpus;
        unsigned long next_balance;     /* in jiffy units */
} nohz ____cacheline_aligned;

static inline int find_new_ilb(void)
{
        int ilb = cpumask_first(nohz.idle_cpus_mask);

        if (ilb < nr_cpu_ids && idle_cpu(ilb))
                return ilb;

        return nr_cpu_ids;
}

/*
 * Kick a CPU to do the nohz balancing, if it is time for it. We pick the
 * nohz_load_balancer CPU (if there is one) otherwise fallback to any idle
 * CPU (if there is one).
 */
static void nohz_balancer_kick(void)
{
        int ilb_cpu;

        nohz.next_balance++;

        ilb_cpu = find_new_ilb();

        if (ilb_cpu >= nr_cpu_ids)
                return;

        if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu)))
                return;
        /*
         * Use smp_send_reschedule() instead of resched_cpu().
         * This way we generate a sched IPI on the target cpu which
         * is idle. And the softirq performing nohz idle load balance
         * will be run before returning from the IPI.
         */
        smp_send_reschedule(ilb_cpu);
        return;
}

static inline void nohz_balance_exit_idle(int cpu)
{
        if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
                /*
                 * Completely isolated CPUs don't ever set, so we must test.
                 */
                if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
                        cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
                        atomic_dec(&nohz.nr_cpus);
                }
                clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
        }
}

static inline void set_cpu_sd_state_busy(void)
{
        struct sched_domain *sd;
        int cpu = smp_processor_id();

        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_busy, cpu));

        if (!sd || !sd->nohz_idle)
                goto unlock;
        sd->nohz_idle = 0;

        atomic_inc(&sd->groups->sgc->nr_busy_cpus);
unlock:
        rcu_read_unlock();
}

void set_cpu_sd_state_idle(void)
{
        struct sched_domain *sd;
        int cpu = smp_processor_id();

        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_busy, cpu));

        if (!sd || sd->nohz_idle)
                goto unlock;
        sd->nohz_idle = 1;

        atomic_dec(&sd->groups->sgc->nr_busy_cpus);
unlock:
        rcu_read_unlock();
}

/*
 * This routine will record that the cpu is going idle with tick stopped.
 * This info will be used in performing idle load balancing in the future.
 */
void nohz_balance_enter_idle(int cpu)
{
        /*
         * If this cpu is going down, then nothing needs to be done.
         */
        if (!cpu_active(cpu))
                return;

        if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
                return;

        /*
         * If we're a completely isolated CPU, we don't play.
         */
        if (on_null_domain(cpu_rq(cpu)))
                return;

        cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
        atomic_inc(&nohz.nr_cpus);
        set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
}

static int sched_ilb_notifier(struct notifier_block *nfb,
                                        unsigned long action, void *hcpu)
{
        switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_DYING:
                nohz_balance_exit_idle(smp_processor_id());
                return NOTIFY_OK;
        default:
                return NOTIFY_DONE;
        }
}
#endif

static DEFINE_SPINLOCK(balancing);

/*
 * Scale the max load_balance interval with the number of CPUs in the system.
 * This trades load-balance latency on larger machines for less cross talk.
 */
void update_max_interval(void)
{
        max_load_balance_interval = HZ*num_online_cpus()/10;
}

/*
 * It checks each scheduling domain to see if it is due to be balanced,
 * and initiates a balancing operation if so.
 *
 * Balancing parameters are set up in init_sched_domains.
 */
static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
{
        int continue_balancing = 1;
        int cpu = rq->cpu;
        unsigned long interval;
        struct sched_domain *sd;
        /* Earliest time when we have to do rebalance again */
        unsigned long next_balance = jiffies + 60*HZ;
        int update_next_balance = 0;
        int need_serialize, need_decay = 0;
        u64 max_cost = 0;

        update_blocked_averages(cpu);

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                /*
                 * Decay the newidle max times here because this is a regular
                 * visit to all the domains. Decay ~1% per second.
                 */
                if (time_after(jiffies, sd->next_decay_max_lb_cost)) {
                        sd->max_newidle_lb_cost =
                                (sd->max_newidle_lb_cost * 253) / 256;
                        sd->next_decay_max_lb_cost = jiffies + HZ;
                        need_decay = 1;
                }
                max_cost += sd->max_newidle_lb_cost;

                if (!(sd->flags & SD_LOAD_BALANCE))
                        continue;

                /*
                 * Stop the load balance at this level. There is another
                 * CPU in our sched group which is doing load balancing more
                 * actively.
                 */
                if (!continue_balancing) {
                        if (need_decay)
                                continue;
                        break;
                }

                interval = get_sd_balance_interval(sd, idle != CPU_IDLE);

                need_serialize = sd->flags & SD_SERIALIZE;
                if (need_serialize) {
                        if (!spin_trylock(&balancing))
                                goto out;
                }

                if (time_after_eq(jiffies, sd->last_balance + interval)) {
                        if (load_balance(cpu, rq, sd, idle, &continue_balancing)) {
                                /*
                                 * The LBF_DST_PINNED logic could have changed
                                 * env->dst_cpu, so we can't know our idle
                                 * state even if we migrated tasks. Update it.
                                 */
                                idle = idle_cpu(cpu) ? CPU_IDLE : CPU_NOT_IDLE;
                        }
                        sd->last_balance = jiffies;
                        interval = get_sd_balance_interval(sd, idle != CPU_IDLE);
                }
                if (need_serialize)
                        spin_unlock(&balancing);
out:
                if (time_after(next_balance, sd->last_balance + interval)) {
                        next_balance = sd->last_balance + interval;
                        update_next_balance = 1;
                }
        }
        if (need_decay) {
                /*
                 * Ensure the rq-wide value also decays but keep it at a
                 * reasonable floor to avoid funnies with rq->avg_idle.
                 */
                rq->max_idle_balance_cost =
                        max((u64)sysctl_sched_migration_cost, max_cost);
        }
        rcu_read_unlock();

        /*
         * next_balance will be updated only when there is a need.
         * When the cpu is attached to null domain for ex, it will not be
         * updated.
         */
        if (likely(update_next_balance))
                rq->next_balance = next_balance;
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
 * rebalancing for all the cpus for whom scheduler ticks are stopped.
 */
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
{
        int this_cpu = this_rq->cpu;
        struct rq *rq;
        int balance_cpu;

        if (idle != CPU_IDLE ||
            !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
                goto end;

        for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
                if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
                        continue;

                /*
                 * If this cpu gets work to do, stop the load balancing
                 * work being done for other cpus. Next load
                 * balancing owner will pick it up.
                 */
                if (need_resched())
                        break;

                rq = cpu_rq(balance_cpu);

                /*
                 * If time for next balance is due,
                 * do the balance.
                 */
                if (time_after_eq(jiffies, rq->next_balance)) {
                        raw_spin_lock_irq(&rq->lock);
                        update_rq_clock(rq);
                        update_idle_cpu_load(rq);
                        raw_spin_unlock_irq(&rq->lock);
                        rebalance_domains(rq, CPU_IDLE);
                }

                if (time_after(this_rq->next_balance, rq->next_balance))
                        this_rq->next_balance = rq->next_balance;
        }
        nohz.next_balance = this_rq->next_balance;
end:
        clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
}

/*
 * Current heuristic for kicking the idle load balancer in the presence
 * of an idle cpu is the system.
 *   - This rq has more than one task.
 *   - At any scheduler domain level, this cpu's scheduler group has multiple
 *     busy cpu's exceeding the group's capacity.
 *   - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
 *     domain span are idle.
 */
static inline int nohz_kick_needed(struct rq *rq)
{
        unsigned long now = jiffies;
        struct sched_domain *sd;
        struct sched_group_capacity *sgc;
        int nr_busy, cpu = rq->cpu;

        if (unlikely(rq->idle_balance))
                return 0;

       /*
        * We may be recently in ticked or tickless idle mode. At the first
        * busy tick after returning from idle, we will update the busy stats.
        */
        set_cpu_sd_state_busy();
        nohz_balance_exit_idle(cpu);

        /*
         * None are in tickless mode and hence no need for NOHZ idle load
         * balancing.
         */
        if (likely(!atomic_read(&nohz.nr_cpus)))
                return 0;

        if (time_before(now, nohz.next_balance))
                return 0;

        if (rq->nr_running >= 2)
                goto need_kick;

        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_busy, cpu));

        if (sd) {
                sgc = sd->groups->sgc;
                nr_busy = atomic_read(&sgc->nr_busy_cpus);

                if (nr_busy > 1)
                        goto need_kick_unlock;
        }

        sd = rcu_dereference(per_cpu(sd_asym, cpu));

        if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
                                  sched_domain_span(sd)) < cpu))
                goto need_kick_unlock;

        rcu_read_unlock();
        return 0;

need_kick_unlock:
        rcu_read_unlock();
need_kick:
        return 1;
}
#else
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
#endif

/*
 * run_rebalance_domains is triggered when needed from the scheduler tick.
 * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
 */
static void run_rebalance_domains(struct softirq_action *h)
{
        struct rq *this_rq = this_rq();
        enum cpu_idle_type idle = this_rq->idle_balance ?
                                                CPU_IDLE : CPU_NOT_IDLE;

        rebalance_domains(this_rq, idle);

        /*
         * If this cpu has a pending nohz_balance_kick, then do the
         * balancing on behalf of the other idle cpus whose ticks are
         * stopped.
         */
        nohz_idle_balance(this_rq, idle);
}

/*
 * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
 */
void trigger_load_balance(struct rq *rq)
{
        /* Don't need to rebalance while attached to NULL domain */
        if (unlikely(on_null_domain(rq)))
                return;

        if (time_after_eq(jiffies, rq->next_balance))
                raise_softirq(SCHED_SOFTIRQ);
#ifdef CONFIG_NO_HZ_COMMON
        if (nohz_kick_needed(rq))
                nohz_balancer_kick();
#endif
}

static void rq_online_fair(struct rq *rq)
{
        update_sysctl();

        update_runtime_enabled(rq);
}

static void rq_offline_fair(struct rq *rq)
{
        update_sysctl();

        /* Ensure any throttled groups are reachable by pick_next_task */
        unthrottle_offline_cfs_rqs(rq);
}

#endif /* CONFIG_SMP */

/*
 * scheduler tick hitting a task of our scheduling class:
 */
static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &curr->se;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                entity_tick(cfs_rq, se, queued);
        }

        if (numabalancing_enabled)
                task_tick_numa(rq, curr);

        update_rq_runnable_avg(rq, 1);
}

/*
 * called on fork with the child task as argument from the parent's context
 *  - child not yet on the tasklist
 *  - preemption disabled
 */
static void task_fork_fair(struct task_struct *p)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se, *curr;
        int this_cpu = smp_processor_id();
        struct rq *rq = this_rq();
        unsigned long flags;

        raw_spin_lock_irqsave(&rq->lock, flags);

        update_rq_clock(rq);

        cfs_rq = task_cfs_rq(current);
        curr = cfs_rq->curr;

        /*
         * Not only the cpu but also the task_group of the parent might have
         * been changed after parent->se.parent,cfs_rq were copied to
         * child->se.parent,cfs_rq. So call __set_task_cpu() to make those
         * of child point to valid ones.
         */
        rcu_read_lock();
        __set_task_cpu(p, this_cpu);
        rcu_read_unlock();

        update_curr(cfs_rq);

        if (curr)
                se->vruntime = curr->vruntime;
        place_entity(cfs_rq, se, 1);

        if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) {
                /*
                 * Upon rescheduling, sched_class::put_prev_task() will place
                 * 'current' within the tree based on its new key value.
                 */
                swap(curr->vruntime, se->vruntime);
                resched_task(rq->curr);
        }

        se->vruntime -= cfs_rq->min_vruntime;

        raw_spin_unlock_irqrestore(&rq->lock, flags);
}

/*
 * Priority of the task has changed. Check to see if we preempt
 * the current task.
 */
static void
prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
{
        if (!p->se.on_rq)
                return;

        /*
         * Reschedule if we are currently running on this runqueue and
         * our priority decreased, or if we are not currently running on
         * this runqueue and our priority is higher than the current's
         */
        if (rq->curr == p) {
                if (p->prio > oldprio)
                        resched_task(rq->curr);
        } else
                check_preempt_curr(rq, p, 0);
}

static void switched_from_fair(struct rq *rq, struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        /*
         * Ensure the task's vruntime is normalized, so that when it's
         * switched back to the fair class the enqueue_entity(.flags=0) will
         * do the right thing.
         *
         * If it's on_rq, then the dequeue_entity(.flags=0) will already
         * have normalized the vruntime, if it's !on_rq, then only when
         * the task is sleeping will it still have non-normalized vruntime.
         */
        if (!p->on_rq && p->state != TASK_RUNNING) {
                /*
                 * Fix up our vruntime so that the current sleep doesn't
                 * cause 'unlimited' sleep bonus.
                 */
                place_entity(cfs_rq, se, 0);
                se->vruntime -= cfs_rq->min_vruntime;
        }

#ifdef CONFIG_SMP
        /*
        * Remove our load from contribution when we leave sched_fair
        * and ensure we don't carry in an old decay_count if we
        * switch back.
        */
        if (se->avg.decay_count) {
                __synchronize_entity_decay(se);
                subtract_blocked_load_contrib(cfs_rq, se->avg.load_avg_contrib);
        }
#endif
}

/*
 * We switched to the sched_fair class.
 */
static void switched_to_fair(struct rq *rq, struct task_struct *p)
{
        struct sched_entity *se = &p->se;
#ifdef CONFIG_FAIR_GROUP_SCHED
        /*
         * Since the real-depth could have been changed (only FAIR
         * class maintain depth value), reset depth properly.
         */
        se->depth = se->parent ? se->parent->depth + 1 : 0;
#endif
        if (!se->on_rq)
                return;

        /*
         * We were most likely switched from sched_rt, so
         * kick off the schedule if running, otherwise just see
         * if we can still preempt the current task.
         */
        if (rq->curr == p)
                resched_task(rq->curr);
        else
                check_preempt_curr(rq, p, 0);
}

/* Account for a task changing its policy or group.
 *
 * This routine is mostly called to set cfs_rq->curr field when a task
 * migrates between groups/classes.
 */
static void set_curr_task_fair(struct rq *rq)
{
        struct sched_entity *se = &rq->curr->se;

        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);

                set_next_entity(cfs_rq, se);
                /* ensure bandwidth has been allocated on our new cfs_rq */
                account_cfs_rq_runtime(cfs_rq, 0);
        }
}

void init_cfs_rq(struct cfs_rq *cfs_rq)
{
        cfs_rq->tasks_timeline = RB_ROOT;
        cfs_rq->min_vruntime = (u64)(-(1LL << 20));
#ifndef CONFIG_64BIT
        cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
#ifdef CONFIG_SMP
        atomic64_set(&cfs_rq->decay_counter, 1);
        atomic_long_set(&cfs_rq->removed_load, 0);
#endif
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void task_move_group_fair(struct task_struct *p, int on_rq)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq;

        /*
         * If the task was not on the rq at the time of this cgroup movement
         * it must have been asleep, sleeping tasks keep their ->vruntime
         * absolute on their old rq until wakeup (needed for the fair sleeper
         * bonus in place_entity()).
         *
         * If it was on the rq, we've just 'preempted' it, which does convert
         * ->vruntime to a relative base.
         *
         * Make sure both cases convert their relative position when migrating
         * to another cgroup's rq. This does somewhat interfere with the
         * fair sleeper stuff for the first placement, but who cares.
         */
        /*
         * When !on_rq, vruntime of the task has usually NOT been normalized.
         * But there are some cases where it has already been normalized:
         *
         * - Moving a forked child which is waiting for being woken up by
         *   wake_up_new_task().
         * - Moving a task which has been woken up by try_to_wake_up() and
         *   waiting for actually being woken up by sched_ttwu_pending().
         *
         * To prevent boost or penalty in the new cfs_rq caused by delta
         * min_vruntime between the two cfs_rqs, we skip vruntime adjustment.
         */
        if (!on_rq && (!se->sum_exec_runtime || p->state == TASK_WAKING))
                on_rq = 1;

        if (!on_rq)
                se->vruntime -= cfs_rq_of(se)->min_vruntime;
        set_task_rq(p, task_cpu(p));
        se->depth = se->parent ? se->parent->depth + 1 : 0;
        if (!on_rq) {
                cfs_rq = cfs_rq_of(se);
                se->vruntime += cfs_rq->min_vruntime;
#ifdef CONFIG_SMP
                /*
                 * migrate_task_rq_fair() will have removed our previous
                 * contribution, but we must synchronize for ongoing future
                 * decay.
                 */
                se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);
                cfs_rq->blocked_load_avg += se->avg.load_avg_contrib;
#endif
        }
}

void free_fair_sched_group(struct task_group *tg)
{
        int i;

        destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));

        for_each_possible_cpu(i) {
                if (tg->cfs_rq)
                        kfree(tg->cfs_rq[i]);
                if (tg->se)
                        kfree(tg->se[i]);
        }

        kfree(tg->cfs_rq);
        kfree(tg->se);
}

int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se;
        int i;

        tg->cfs_rq = kzalloc(sizeof(cfs_rq) * nr_cpu_ids, GFP_KERNEL);
        if (!tg->cfs_rq)
                goto err;
        tg->se = kzalloc(sizeof(se) * nr_cpu_ids, GFP_KERNEL);
        if (!tg->se)
                goto err;

        tg->shares = NICE_0_LOAD;

        init_cfs_bandwidth(tg_cfs_bandwidth(tg));

        for_each_possible_cpu(i) {
                cfs_rq = kzalloc_node(sizeof(struct cfs_rq),
                                      GFP_KERNEL, cpu_to_node(i));
                if (!cfs_rq)
                        goto err;

                se = kzalloc_node(sizeof(struct sched_entity),
                                  GFP_KERNEL, cpu_to_node(i));
                if (!se)
                        goto err_free_rq;

                init_cfs_rq(cfs_rq);
                init_tg_cfs_entry(tg, cfs_rq, se, i, parent->se[i]);
        }

        return 1;

err_free_rq:
        kfree(cfs_rq);
err:
        return 0;
}

void unregister_fair_sched_group(struct task_group *tg, int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long flags;

        /*
        * Only empty task groups can be destroyed; so we can speculatively
        * check on_list without danger of it being re-added.
        */
        if (!tg->cfs_rq[cpu]->on_list)
                return;

        raw_spin_lock_irqsave(&rq->lock, flags);
        list_del_leaf_cfs_rq(tg->cfs_rq[cpu]);
        raw_spin_unlock_irqrestore(&rq->lock, flags);
}

void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
                        struct sched_entity *se, int cpu,
                        struct sched_entity *parent)
{
        struct rq *rq = cpu_rq(cpu);

        cfs_rq->tg = tg;
        cfs_rq->rq = rq;
        init_cfs_rq_runtime(cfs_rq);

        tg->cfs_rq[cpu] = cfs_rq;
        tg->se[cpu] = se;

        /* se could be NULL for root_task_group */
        if (!se)
                return;

        if (!parent) {
                se->cfs_rq = &rq->cfs;
                se->depth = 0;
        } else {
                se->cfs_rq = parent->my_q;
                se->depth = parent->depth + 1;
        }

        se->my_q = cfs_rq;
        /* guarantee group entities always have weight */
        update_load_set(&se->load, NICE_0_LOAD);
        se->parent = parent;
}

static DEFINE_MUTEX(shares_mutex);

int sched_group_set_shares(struct task_group *tg, unsigned long shares)
{
        int i;
        unsigned long flags;

        /*
         * We can't change the weight of the root cgroup.
         */
        if (!tg->se[0])
                return -EINVAL;

        shares = clamp(shares, scale_load(MIN_SHARES), scale_load(MAX_SHARES));

        mutex_lock(&shares_mutex);
        if (tg->shares == shares)
                goto done;

        tg->shares = shares;
        for_each_possible_cpu(i) {
                struct rq *rq = cpu_rq(i);
                struct sched_entity *se;

                se = tg->se[i];
                /* Propagate contribution to hierarchy */
                raw_spin_lock_irqsave(&rq->lock, flags);

                /* Possible calls to update_curr() need rq clock */
                update_rq_clock(rq);
                for_each_sched_entity(se)
                        update_cfs_shares(group_cfs_rq(se));
                raw_spin_unlock_irqrestore(&rq->lock, flags);
        }

done:
        mutex_unlock(&shares_mutex);
        return 0;
}
#else /* CONFIG_FAIR_GROUP_SCHED */

void free_fair_sched_group(struct task_group *tg) { }

int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
{
        return 1;
}

void unregister_fair_sched_group(struct task_group *tg, int cpu) { }

#endif /* CONFIG_FAIR_GROUP_SCHED */


static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
{
        struct sched_entity *se = &task->se;
        unsigned int rr_interval = 0;

        /*
         * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
         * idle runqueue:
         */
        if (rq->cfs.load.weight)
                rr_interval = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));

        return rr_interval;
}

/*
 * All the scheduling class methods:
 */
const struct sched_class fair_sched_class = {
        .next                   = &idle_sched_class,
        .enqueue_task           = enqueue_task_fair,
        .dequeue_task           = dequeue_task_fair,
        .yield_task             = yield_task_fair,
        .yield_to_task          = yield_to_task_fair,

        .check_preempt_curr     = check_preempt_wakeup,

        .pick_next_task         = pick_next_task_fair,
        .put_prev_task          = put_prev_task_fair,

#ifdef CONFIG_SMP
        .select_task_rq         = select_task_rq_fair,
        .migrate_task_rq        = migrate_task_rq_fair,

        .rq_online              = rq_online_fair,
        .rq_offline             = rq_offline_fair,

        .task_waking            = task_waking_fair,
#endif

        .set_curr_task          = set_curr_task_fair,
        .task_tick              = task_tick_fair,
        .task_fork              = task_fork_fair,

        .prio_changed           = prio_changed_fair,
        .switched_from          = switched_from_fair,
        .switched_to            = switched_to_fair,

        .get_rr_interval        = get_rr_interval_fair,

#ifdef CONFIG_FAIR_GROUP_SCHED
        .task_move_group        = task_move_group_fair,
#endif
};

#ifdef CONFIG_SCHED_DEBUG
void print_cfs_stats(struct seq_file *m, int cpu)
{
        struct cfs_rq *cfs_rq;

        rcu_read_lock();
        for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
                print_cfs_rq(m, cpu, cfs_rq);
        rcu_read_unlock();
}
#endif

__init void init_sched_fair_class(void)
{
#ifdef CONFIG_SMP
        open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);

#ifdef CONFIG_NO_HZ_COMMON
        nohz.next_balance = jiffies;
        zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
        cpu_notifier(sched_ilb_notifier, 0);
#endif
#endif /* SMP */

}