sched: Cleanup select_task_rq_fair()

[mirror_ubuntu-jammy-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>

/*
 * Targeted preemption latency for CPU-bound tasks:
 * (default: 5ms * (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 = 5000000ULL;

/*
 * Minimal preemption granularity for CPU-bound tasks:
 * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_min_granularity = 1000000ULL;

/*
 * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
 */
static unsigned int sched_nr_latency = 5;

/*
 * 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;

/*
 * sys_sched_yield() compat mode
 *
 * This option switches the agressive yield implementation of the
 * old scheduler back on.
 */
unsigned int __read_mostly sysctl_sched_compat_yield;

/*
 * 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;

const_debug unsigned int sysctl_sched_migration_cost = 500000UL;

static 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;
}

/* Given a group's cfs_rq on one cpu, return its corresponding cfs_rq on
 * another cpu ('this_cpu')
 */
static inline struct cfs_rq *cpu_cfs_rq(struct cfs_rq *cfs_rq, int this_cpu)
{
        return cfs_rq->tg->cfs_rq[this_cpu];
}

/* 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 int
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        if (se->cfs_rq == pse->cfs_rq)
                return 1;

        return 0;
}

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

/* return depth at which a sched entity is present in the hierarchy */
static inline int depth_se(struct sched_entity *se)
{
        int depth = 0;

        for_each_sched_entity(se)
                depth++;

        return depth;
}

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 = depth_se(*se);
        pse_depth = depth_se(*pse);

        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 struct cfs_rq *cpu_cfs_rq(struct cfs_rq *cfs_rq, int this_cpu)
{
        return &cpu_rq(this_cpu)->cfs;
}

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

static inline int
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        return 1;
}

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 */


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

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

        return min_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 inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        return se->vruntime - cfs_rq->min_vruntime;
}

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);
        }

        cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
}

/*
 * 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;
        s64 key = entity_key(cfs_rq, se);
        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 (key < entity_key(cfs_rq, 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);
}

static struct sched_entity *__pick_next_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_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:
 */

#ifdef CONFIG_SCHED_DEBUG
int sched_nr_latency_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);

        if (ret || !write)
                return ret;

        sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
                                        sysctl_sched_min_granularity);

        return 0;
}
#endif

/*
 * delta /= w
 */
static inline unsigned long
calc_delta_fair(unsigned long delta, struct sched_entity *se)
{
        if (unlikely(se->load.weight != NICE_0_LOAD))
                delta = calc_delta_mine(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 (sysctl_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_mine(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);
}

/*
 * Update the current task's runtime statistics. Skip current tasks that
 * are not in our scheduling class.
 */
static inline void
__update_curr(struct cfs_rq *cfs_rq, struct sched_entity *curr,
              unsigned long delta_exec)
{
        unsigned long delta_exec_weighted;

        schedstat_set(curr->exec_max, max((u64)delta_exec, curr->exec_max));

        curr->sum_exec_runtime += delta_exec;
        schedstat_add(cfs_rq, exec_clock, delta_exec);
        delta_exec_weighted = calc_delta_fair(delta_exec, curr);
        curr->vruntime += delta_exec_weighted;
        update_min_vruntime(cfs_rq);
}

static void update_curr(struct cfs_rq *cfs_rq)
{
        struct sched_entity *curr = cfs_rq->curr;
        u64 now = rq_of(cfs_rq)->clock;
        unsigned long delta_exec;

        if (unlikely(!curr))
                return;

        /*
         * Get the amount of time the current task was running
         * since the last time we changed load (this cannot
         * overflow on 32 bits):
         */
        delta_exec = (unsigned long)(now - curr->exec_start);
        if (!delta_exec)
                return;

        __update_curr(cfs_rq, curr, delta_exec);
        curr->exec_start = now;

        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);
        }
}

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

/*
 * 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->wait_max, max(se->wait_max,
                        rq_of(cfs_rq)->clock - se->wait_start));
        schedstat_set(se->wait_count, se->wait_count + 1);
        schedstat_set(se->wait_sum, se->wait_sum +
                        rq_of(cfs_rq)->clock - se->wait_start);
#ifdef CONFIG_SCHEDSTATS
        if (entity_is_task(se)) {
                trace_sched_stat_wait(task_of(se),
                        rq_of(cfs_rq)->clock - se->wait_start);
        }
#endif
        schedstat_set(se->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_of(cfs_rq)->clock;
}

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

#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
static void
add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
{
        cfs_rq->task_weight += weight;
}
#else
static inline void
add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
{
}
#endif

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))
                inc_cpu_load(rq_of(cfs_rq), se->load.weight);
        if (entity_is_task(se)) {
                add_cfs_task_weight(cfs_rq, se->load.weight);
                list_add(&se->group_node, &cfs_rq->tasks);
        }
        cfs_rq->nr_running++;
        se->on_rq = 1;
}

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))
                dec_cpu_load(rq_of(cfs_rq), se->load.weight);
        if (entity_is_task(se)) {
                add_cfs_task_weight(cfs_rq, -se->load.weight);
                list_del_init(&se->group_node);
        }
        cfs_rq->nr_running--;
        se->on_rq = 0;
}

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->sleep_start) {
                u64 delta = rq_of(cfs_rq)->clock - se->sleep_start;

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

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

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

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

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

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

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

                if (tsk) {
                        if (tsk->in_iowait) {
                                se->iowait_sum += delta;
                                se->iowait_count++;
                                trace_sched_stat_iowait(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 && sched_feat(FAIR_SLEEPERS)) {
                unsigned long thresh = sysctl_sched_latency;

                /*
                 * Convert the sleeper threshold into virtual time.
                 * SCHED_IDLE is a special sub-class.  We care about
                 * fairness only relative to other SCHED_IDLE tasks,
                 * all of which have the same weight.
                 */
                if (sched_feat(NORMALIZED_SLEEPER) && (!entity_is_task(se) ||
                                 task_of(se)->policy != SCHED_IDLE))
                        thresh = calc_delta_fair(thresh, se);

                /*
                 * 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. */
        vruntime = max_vruntime(se->vruntime, vruntime);

        se->vruntime = vruntime;
}

static void
enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);
        account_entity_enqueue(cfs_rq, se);

        if (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);
}

static void __clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (!se || cfs_rq->last == se)
                cfs_rq->last = NULL;

        if (!se || cfs_rq->next == se)
                cfs_rq->next = NULL;
}

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        for_each_sched_entity(se)
                __clear_buddies(cfs_rq_of(se), se);
}

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

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

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

        clear_buddies(cfs_rq, se);

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

        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);
        }
}

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->slice_max = max(se->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);

static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
{
        struct sched_entity *se = __pick_next_entity(cfs_rq);

        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, se) < 1)
                return cfs_rq->next;

        if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, se) < 1)
                return cfs_rq->last;

        return se;
}

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);

        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);
        }
        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);

#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 || !sched_feat(WAKEUP_PREEMPT))
                check_preempt_tick(cfs_rq, curr);
}

/**************************************************
 * 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 (hrtick_enabled(rq) && 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 (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 wakeup)
{
        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, wakeup);
                wakeup = 1;
        }

        hrtick_update(rq);
}

/*
 * 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 sleep)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                dequeue_entity(cfs_rq, se, sleep);
                /* Don't dequeue parent if it has other entities besides us */
                if (cfs_rq->load.weight)
                        break;
                sleep = 1;
        }

        hrtick_update(rq);
}

/*
 * sched_yield() support is very simple - we dequeue and enqueue.
 *
 * If compat_yield is turned on then we requeue to the end of the tree.
 */
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 *rightmost, *se = &curr->se;

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

        clear_buddies(cfs_rq, se);

        if (likely(!sysctl_sched_compat_yield) && curr->policy != SCHED_BATCH) {
                update_rq_clock(rq);
                /*
                 * Update run-time statistics of the 'current'.
                 */
                update_curr(cfs_rq);

                return;
        }
        /*
         * Find the rightmost entry in the rbtree:
         */
        rightmost = __pick_last_entity(cfs_rq);
        /*
         * Already in the rightmost position?
         */
        if (unlikely(!rightmost || entity_before(rightmost, se)))
                return;

        /*
         * Minimally necessary key value to be last in the tree:
         * Upon rescheduling, sched_class::put_prev_task() will place
         * 'current' within the tree based on its new key value.
         */
        se->vruntime = rightmost->vruntime + 1;
}

#ifdef CONFIG_SMP

#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.
 *
 * The problem is that perfectly aligning the shares is rather expensive, hence
 * we try to avoid doing that too often - see update_shares(), which ratelimits
 * this change.
 *
 * We compensate this by not only taking the current delta into account, but
 * also considering the delta between when the shares were last adjusted and
 * now.
 *
 * We still saw a performance dip, some tracing learned us that between
 * cgroup:/ and cgroup:/foo balancing the number of affine wakeups increased
 * significantly. Therefore try to bias the error in direction of failing
 * the affine wakeup.
 *
 */
static long effective_load(struct task_group *tg, int cpu,
                long wl, long wg)
{
        struct sched_entity *se = tg->se[cpu];

        if (!tg->parent)
                return wl;

        /*
         * By not taking the decrease of shares on the other cpu into
         * account our error leans towards reducing the affine wakeups.
         */
        if (!wl && sched_feat(ASYM_EFF_LOAD))
                return wl;

        for_each_sched_entity(se) {
                long S, rw, s, a, b;
                long more_w;

                /*
                 * Instead of using this increment, also add the difference
                 * between when the shares were last updated and now.
                 */
                more_w = se->my_q->load.weight - se->my_q->rq_weight;
                wl += more_w;
                wg += more_w;

                S = se->my_q->tg->shares;
                s = se->my_q->shares;
                rw = se->my_q->rq_weight;

                a = S*(rw + wl);
                b = S*rw + s*wg;

                wl = s*(a-b);

                if (likely(b))
                        wl /= b;

                /*
                 * Assume the group is already running and will
                 * thus already be accounted for in the weight.
                 *
                 * That is, moving shares between CPUs, does not
                 * alter the group weight.
                 */
                wg = 0;
        }

        return wl;
}

#else

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

#endif

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

        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) {
               if (sched_feat(SYNC_LESS) &&
                   (curr->se.avg_overlap > sysctl_sched_migration_cost ||
                    p->se.avg_overlap > sysctl_sched_migration_cost))
                       sync = 0;
        } else {
                if (sched_feat(SYNC_MORE) &&
                    (curr->se.avg_overlap < sysctl_sched_migration_cost &&
                     p->se.avg_overlap < sysctl_sched_migration_cost))
                        sync = 1;
        }

        /*
         * 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;

        imbalance = 100 + (sd->imbalance_pct - 100) / 2;

        /*
         * 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.
         */
        balanced = !this_load ||
                100*(this_load + effective_load(tg, this_cpu, weight, weight)) <=
                imbalance*(load + effective_load(tg, prev_cpu, 0, weight));

        /*
         * 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.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.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 load_idx)
{
        struct sched_group *idlest = NULL, *this = NULL, *group = sd->groups;
        unsigned long min_load = ULONG_MAX, this_load = 0;
        int imbalance = 100 + (sd->imbalance_pct-100)/2;

        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),
                                        &p->cpus_allowed))
                        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 power of the group */
                avg_load = (avg_load * SCHED_LOAD_SCALE) / group->cpu_power;

                if (local_group) {
                        this_load = avg_load;
                        this = group;
                } 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), &p->cpus_allowed) {
                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, struct sched_domain *sd, int target)
{
        int cpu = smp_processor_id();
        int prev_cpu = task_cpu(p);
        int i;

        /*
         * If this domain spans both cpu and prev_cpu (see the SD_WAKE_AFFINE
         * test in select_task_rq_fair) and the prev_cpu is idle then that's
         * always a better target than the current cpu.
         */
        if (target == cpu) {
                if (!cpu_rq(prev_cpu)->cfs.nr_running)
                        target = prev_cpu;
        }

        /*
         * Otherwise, iterate the domain and find an elegible idle cpu.
         */
        if (target == -1 || target == cpu) {
                for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
                        if (!cpu_rq(i)->cfs.nr_running) {
                                target = i;
                                break;
                        }
                }
        }

        return target;
}

/*
 * sched_balance_self: balance the current task (running on cpu) in domains
 * that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
 * SD_BALANCE_EXEC.
 *
 * Balance, ie. select the least loaded group.
 *
 * Returns the target CPU number, or the same CPU if no balancing is needed.
 *
 * preempt must be disabled.
 */
static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
{
        struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
        int cpu = smp_processor_id();
        int prev_cpu = task_cpu(p);
        int new_cpu = cpu;
        int want_affine = 0;
        int want_sd = 1;
        int sync = wake_flags & WF_SYNC;

        if (sd_flag & SD_BALANCE_WAKE) {
                if (sched_feat(AFFINE_WAKEUPS) &&
                    cpumask_test_cpu(cpu, &p->cpus_allowed))
                        want_affine = 1;
                new_cpu = prev_cpu;
        }

        rcu_read_lock();
        for_each_domain(cpu, tmp) {
                /*
                 * If power savings logic is enabled for a domain, see if we
                 * are not overloaded, if so, don't balance wider.
                 */
                if (tmp->flags & (SD_POWERSAVINGS_BALANCE|SD_PREFER_LOCAL)) {
                        unsigned long power = 0;
                        unsigned long nr_running = 0;
                        unsigned long capacity;
                        int i;

                        for_each_cpu(i, sched_domain_span(tmp)) {
                                power += power_of(i);
                                nr_running += cpu_rq(i)->cfs.nr_running;
                        }

                        capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);

                        if (tmp->flags & SD_POWERSAVINGS_BALANCE)
                                nr_running /= 2;

                        if (nr_running < capacity)
                                want_sd = 0;
                }

                if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
                        int target = -1;

                        /*
                         * If both cpu and prev_cpu are part of this domain,
                         * cpu is a valid SD_WAKE_AFFINE target.
                         */
                        if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
                                target = cpu;

                        /*
                         * If there's an idle sibling in this domain, make that
                         * the wake_affine target instead of the current cpu.
                         *
                         * XXX: should we possibly do this outside of
                         * WAKE_AFFINE, in case the shared cache domain is
                         * smaller than the WAKE_AFFINE domain?
                         */
                        if (tmp->flags & SD_PREFER_SIBLING)
                                target = select_idle_sibling(p, tmp, target);

                        if (target >= 0) {
                                affine_sd = tmp;
                                want_affine = 0;
                                cpu = target;
                        }
                }

                if (!want_sd && !want_affine)
                        break;

                if (!(tmp->flags & sd_flag))
                        continue;

                if (want_sd)
                        sd = tmp;
        }

        if (sched_feat(LB_SHARES_UPDATE)) {
                /*
                 * Pick the largest domain to update shares over
                 */
                tmp = sd;
                if (affine_sd && (!tmp ||
                                  cpumask_weight(sched_domain_span(affine_sd)) >
                                  cpumask_weight(sched_domain_span(sd))))
                        tmp = affine_sd;

                if (tmp)
                        update_shares(tmp);
        }

        if (affine_sd && wake_affine(affine_sd, p, sync)) {
                new_cpu = cpu;
                goto out;
        }

        while (sd) {
                int load_idx = sd->forkexec_idx;
                struct sched_group *group;
                int weight;

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

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

                group = find_idlest_group(sd, p, cpu, load_idx);
                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 = cpumask_weight(sched_domain_span(sd));
                sd = NULL;
                for_each_domain(cpu, tmp) {
                        if (weight <= cpumask_weight(sched_domain_span(tmp)))
                                break;
                        if (tmp->flags & sd_flag)
                                sd = tmp;
                }
                /* while loop will break here if sd == NULL */
        }

out:
        rcu_read_unlock();
        return new_cpu;
}
#endif /* CONFIG_SMP */

/*
 * Adaptive granularity
 *
 * se->avg_wakeup gives the average time a task runs until it does a wakeup,
 * with the limit of wakeup_gran -- when it never does a wakeup.
 *
 * So the smaller avg_wakeup is the faster we want this task to preempt,
 * but we don't want to treat the preemptee unfairly and therefore allow it
 * to run for at least the amount of time we'd like to run.
 *
 * NOTE: we use 2*avg_wakeup to increase the probability of actually doing one
 *
 * NOTE: we use *nr_running to scale with load, this nicely matches the
 *       degrading latency on load.
 */
static unsigned long
adaptive_gran(struct sched_entity *curr, struct sched_entity *se)
{
        u64 this_run = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
        u64 expected_wakeup = 2*se->avg_wakeup * cfs_rq_of(se)->nr_running;
        u64 gran = 0;

        if (this_run < expected_wakeup)
                gran = expected_wakeup - this_run;

        return min_t(s64, gran, sysctl_sched_wakeup_granularity);
}

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

        if (cfs_rq_of(curr)->curr && sched_feat(ADAPTIVE_GRAN))
                gran = adaptive_gran(curr, se);

        /*
         * Since its curr running now, convert the gran from real-time
         * to virtual-time in his units.
         */
        if (sched_feat(ASYM_GRAN)) {
                /*
                 * 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.
                 */
                if (unlikely(se->load.weight != NICE_0_LOAD))
                        gran = calc_delta_fair(gran, se);
        } else {
                if (unlikely(curr->load.weight != NICE_0_LOAD))
                        gran = calc_delta_fair(gran, curr);
        }

        return gran;
}

/*
 * 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 (likely(task_of(se)->policy != SCHED_IDLE)) {
                for_each_sched_entity(se)
                        cfs_rq_of(se)->last = se;
        }
}

static void set_next_buddy(struct sched_entity *se)
{
        if (likely(task_of(se)->policy != SCHED_IDLE)) {
                for_each_sched_entity(se)
                        cfs_rq_of(se)->next = 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 sync = wake_flags & WF_SYNC;

        update_curr(cfs_rq);

        if (unlikely(rt_prio(p->prio))) {
                resched_task(curr);
                return;
        }

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

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

        /*
         * 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 the idle thread.
         */
        if (sched_feat(LAST_BUDDY) && likely(se->on_rq && curr != rq->idle))
                set_last_buddy(se);
        if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK))
                set_next_buddy(pse);

        /*
         * We can come here with TIF_NEED_RESCHED already set from new task
         * wake up path.
         */
        if (test_tsk_need_resched(curr))
                return;

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

        /* Idle tasks are by definition preempted by everybody. */
        if (unlikely(curr->policy == SCHED_IDLE)) {
                resched_task(curr);
                return;
        }

        if ((sched_feat(WAKEUP_SYNC) && sync) ||
            (sched_feat(WAKEUP_OVERLAP) &&
             (se->avg_overlap < sysctl_sched_migration_cost &&
              pse->avg_overlap < sysctl_sched_migration_cost))) {
                resched_task(curr);
                return;
        }

        if (sched_feat(WAKEUP_RUNNING)) {
                if (pse->avg_running < se->avg_running) {
                        set_next_buddy(pse);
                        resched_task(curr);
                        return;
                }
        }

        if (!sched_feat(WAKEUP_PREEMPT))
                return;

        find_matching_se(&se, &pse);

        BUG_ON(!pse);

        if (wakeup_preempt_entity(se, pse) == 1)
                resched_task(curr);
}

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

        if (unlikely(!cfs_rq->nr_running))
                return NULL;

        do {
                se = pick_next_entity(cfs_rq);
                /*
                 * If se was a buddy, clear it so that it will have to earn
                 * the favour again.
                 *
                 * If se was not a buddy, clear the buddies because neither
                 * was elegible to run, let them earn it again.
                 *
                 * IOW. unconditionally clear buddies.
                 */
                __clear_buddies(cfs_rq, NULL);
                set_next_entity(cfs_rq, se);
                cfs_rq = group_cfs_rq(se);
        } while (cfs_rq);

        p = task_of(se);
        hrtick_start_fair(rq, p);

        return p;
}

/*
 * 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);
        }
}

#ifdef CONFIG_SMP
/**************************************************
 * Fair scheduling class load-balancing methods:
 */

/*
 * Load-balancing iterator. Note: while the runqueue stays locked
 * during the whole iteration, the current task might be
 * dequeued so the iterator has to be dequeue-safe. Here we
 * achieve that by always pre-iterating before returning
 * the current task:
 */
static struct task_struct *
__load_balance_iterator(struct cfs_rq *cfs_rq, struct list_head *next)
{
        struct task_struct *p = NULL;
        struct sched_entity *se;

        if (next == &cfs_rq->tasks)
                return NULL;

        se = list_entry(next, struct sched_entity, group_node);
        p = task_of(se);
        cfs_rq->balance_iterator = next->next;

        return p;
}

static struct task_struct *load_balance_start_fair(void *arg)
{
        struct cfs_rq *cfs_rq = arg;

        return __load_balance_iterator(cfs_rq, cfs_rq->tasks.next);
}

static struct task_struct *load_balance_next_fair(void *arg)
{
        struct cfs_rq *cfs_rq = arg;

        return __load_balance_iterator(cfs_rq, cfs_rq->balance_iterator);
}

static unsigned long
__load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                unsigned long max_load_move, struct sched_domain *sd,
                enum cpu_idle_type idle, int *all_pinned, int *this_best_prio,
                struct cfs_rq *cfs_rq)
{
        struct rq_iterator cfs_rq_iterator;

        cfs_rq_iterator.start = load_balance_start_fair;
        cfs_rq_iterator.next = load_balance_next_fair;
        cfs_rq_iterator.arg = cfs_rq;

        return balance_tasks(this_rq, this_cpu, busiest,
                        max_load_move, sd, idle, all_pinned,
                        this_best_prio, &cfs_rq_iterator);
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static unsigned long
load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                  unsigned long max_load_move,
                  struct sched_domain *sd, enum cpu_idle_type idle,
                  int *all_pinned, int *this_best_prio)
{
        long rem_load_move = max_load_move;
        int busiest_cpu = cpu_of(busiest);
        struct task_group *tg;

        rcu_read_lock();
        update_h_load(busiest_cpu);

        list_for_each_entry_rcu(tg, &task_groups, list) {
                struct cfs_rq *busiest_cfs_rq = tg->cfs_rq[busiest_cpu];
                unsigned long busiest_h_load = busiest_cfs_rq->h_load;
                unsigned long busiest_weight = busiest_cfs_rq->load.weight;
                u64 rem_load, moved_load;

                /*
                 * empty group
                 */
                if (!busiest_cfs_rq->task_weight)
                        continue;

                rem_load = (u64)rem_load_move * busiest_weight;
                rem_load = div_u64(rem_load, busiest_h_load + 1);

                moved_load = __load_balance_fair(this_rq, this_cpu, busiest,
                                rem_load, sd, idle, all_pinned, this_best_prio,
                                tg->cfs_rq[busiest_cpu]);

                if (!moved_load)
                        continue;

                moved_load *= busiest_h_load;
                moved_load = div_u64(moved_load, busiest_weight + 1);

                rem_load_move -= moved_load;
                if (rem_load_move < 0)
                        break;
        }
        rcu_read_unlock();

        return max_load_move - rem_load_move;
}
#else
static unsigned long
load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                  unsigned long max_load_move,
                  struct sched_domain *sd, enum cpu_idle_type idle,
                  int *all_pinned, int *this_best_prio)
{
        return __load_balance_fair(this_rq, this_cpu, busiest,
                        max_load_move, sd, idle, all_pinned,
                        this_best_prio, &busiest->cfs);
}
#endif

static int
move_one_task_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                   struct sched_domain *sd, enum cpu_idle_type idle)
{
        struct cfs_rq *busy_cfs_rq;
        struct rq_iterator cfs_rq_iterator;

        cfs_rq_iterator.start = load_balance_start_fair;
        cfs_rq_iterator.next = load_balance_next_fair;

        for_each_leaf_cfs_rq(busiest, busy_cfs_rq) {
                /*
                 * pass busy_cfs_rq argument into
                 * load_balance_[start|next]_fair iterators
                 */
                cfs_rq_iterator.arg = busy_cfs_rq;
                if (iter_move_one_task(this_rq, this_cpu, busiest, sd, idle,
                                       &cfs_rq_iterator))
                    return 1;
        }

        return 0;
}
#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);
        }
}

/*
 * Share the fairness runtime between parent and child, thus the
 * total amount of pressure for CPU stays equal - new tasks
 * get a chance to run but frequent forkers are not allowed to
 * monopolize the CPU. Note: the parent runqueue is locked,
 * the child is not running yet.
 */
static void task_new_fair(struct rq *rq, struct task_struct *p)
{
        struct cfs_rq *cfs_rq = task_cfs_rq(p);
        struct sched_entity *se = &p->se, *curr = cfs_rq->curr;
        int this_cpu = smp_processor_id();

        sched_info_queued(p);

        update_curr(cfs_rq);
        if (curr)
                se->vruntime = curr->vruntime;
        place_entity(cfs_rq, se, 1);

        /* 'curr' will be NULL if the child belongs to a different group */
        if (sysctl_sched_child_runs_first && this_cpu == task_cpu(p) &&
                        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);
        }

        enqueue_task_fair(rq, p, 0);
}

/*
 * 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, int running)
{
        /*
         * 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 (running) {
                if (p->prio > oldprio)
                        resched_task(rq->curr);
        } else
                check_preempt_curr(rq, p, 0);
}

/*
 * We switched to the sched_fair class.
 */
static void switched_to_fair(struct rq *rq, struct task_struct *p,
                             int running)
{
        /*
         * 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 (running)
                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)
                set_next_entity(cfs_rq_of(se), se);
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void moved_group_fair(struct task_struct *p)
{
        struct cfs_rq *cfs_rq = task_cfs_rq(p);

        update_curr(cfs_rq);
        place_entity(cfs_rq, &p->se, 1);
}
#endif

unsigned int get_rr_interval_fair(struct task_struct *task)
{
        struct sched_entity *se = &task->se;
        unsigned long flags;
        struct rq *rq;
        unsigned int rr_interval = 0;

        /*
         * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
         * idle runqueue:
         */
        rq = task_rq_lock(task, &flags);
        if (rq->cfs.load.weight)
                rr_interval = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
        task_rq_unlock(rq, &flags);

        return rr_interval;
}

/*
 * All the scheduling class methods:
 */
static 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,

        .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,

        .load_balance           = load_balance_fair,
        .move_one_task          = move_one_task_fair,
#endif

        .set_curr_task          = set_curr_task_fair,
        .task_tick              = task_tick_fair,
        .task_new               = task_new_fair,

        .prio_changed           = prio_changed_fair,
        .switched_to            = switched_to_fair,

        .get_rr_interval        = get_rr_interval_fair,

#ifdef CONFIG_FAIR_GROUP_SCHED
        .moved_group            = moved_group_fair,
#endif
};

#ifdef CONFIG_SCHED_DEBUG
static 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