powerpc/spufs: Fix multiple get_spu_context()

[mirror_ubuntu-bionic-kernel.git] / arch / powerpc / platforms / cell / spufs / sched.c

/* sched.c - SPU scheduler.
 *
 * Copyright (C) IBM 2005
 * Author: Mark Nutter <mnutter@us.ibm.com>
 *
 * 2006-03-31   NUMA domains added.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#undef DEBUG

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/completion.h>
#include <linux/vmalloc.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/numa.h>
#include <linux/mutex.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/pid_namespace.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/marker.h>

#include <asm/io.h>
#include <asm/mmu_context.h>
#include <asm/spu.h>
#include <asm/spu_csa.h>
#include <asm/spu_priv1.h>
#include "spufs.h"

struct spu_prio_array {
        DECLARE_BITMAP(bitmap, MAX_PRIO);
        struct list_head runq[MAX_PRIO];
        spinlock_t runq_lock;
        int nr_waiting;
};

static unsigned long spu_avenrun[3];
static struct spu_prio_array *spu_prio;
static struct task_struct *spusched_task;
static struct timer_list spusched_timer;
static struct timer_list spuloadavg_timer;

/*
 * Priority of a normal, non-rt, non-niced'd process (aka nice level 0).
 */
#define NORMAL_PRIO             120

/*
 * Frequency of the spu scheduler tick.  By default we do one SPU scheduler
 * tick for every 10 CPU scheduler ticks.
 */
#define SPUSCHED_TICK           (10)

/*
 * These are the 'tuning knobs' of the scheduler:
 *
 * Minimum timeslice is 5 msecs (or 1 spu scheduler tick, whichever is
 * larger), default timeslice is 100 msecs, maximum timeslice is 800 msecs.
 */
#define MIN_SPU_TIMESLICE       max(5 * HZ / (1000 * SPUSCHED_TICK), 1)
#define DEF_SPU_TIMESLICE       (100 * HZ / (1000 * SPUSCHED_TICK))

#define MAX_USER_PRIO           (MAX_PRIO - MAX_RT_PRIO)
#define SCALE_PRIO(x, prio) \
        max(x * (MAX_PRIO - prio) / (MAX_USER_PRIO / 2), MIN_SPU_TIMESLICE)

/*
 * scale user-nice values [ -20 ... 0 ... 19 ] to time slice values:
 * [800ms ... 100ms ... 5ms]
 *
 * The higher a thread's priority, the bigger timeslices
 * it gets during one round of execution. But even the lowest
 * priority thread gets MIN_TIMESLICE worth of execution time.
 */
void spu_set_timeslice(struct spu_context *ctx)
{
        if (ctx->prio < NORMAL_PRIO)
                ctx->time_slice = SCALE_PRIO(DEF_SPU_TIMESLICE * 4, ctx->prio);
        else
                ctx->time_slice = SCALE_PRIO(DEF_SPU_TIMESLICE, ctx->prio);
}

/*
 * Update scheduling information from the owning thread.
 */
void __spu_update_sched_info(struct spu_context *ctx)
{
        /*
         * assert that the context is not on the runqueue, so it is safe
         * to change its scheduling parameters.
         */
        BUG_ON(!list_empty(&ctx->rq));

        /*
         * 32-Bit assignments are atomic on powerpc, and we don't care about
         * memory ordering here because retrieving the controlling thread is
         * per definition racy.
         */
        ctx->tid = current->pid;

        /*
         * We do our own priority calculations, so we normally want
         * ->static_prio to start with. Unfortunately this field
         * contains junk for threads with a realtime scheduling
         * policy so we have to look at ->prio in this case.
         */
        if (rt_prio(current->prio))
                ctx->prio = current->prio;
        else
                ctx->prio = current->static_prio;
        ctx->policy = current->policy;

        /*
         * TO DO: the context may be loaded, so we may need to activate
         * it again on a different node. But it shouldn't hurt anything
         * to update its parameters, because we know that the scheduler
         * is not actively looking at this field, since it is not on the
         * runqueue. The context will be rescheduled on the proper node
         * if it is timesliced or preempted.
         */
        ctx->cpus_allowed = current->cpus_allowed;

        /* Save the current cpu id for spu interrupt routing. */
        ctx->last_ran = raw_smp_processor_id();
}

void spu_update_sched_info(struct spu_context *ctx)
{
        int node;

        if (ctx->state == SPU_STATE_RUNNABLE) {
                node = ctx->spu->node;

                /*
                 * Take list_mutex to sync with find_victim().
                 */
                mutex_lock(&cbe_spu_info[node].list_mutex);
                __spu_update_sched_info(ctx);
                mutex_unlock(&cbe_spu_info[node].list_mutex);
        } else {
                __spu_update_sched_info(ctx);
        }
}

static int __node_allowed(struct spu_context *ctx, int node)
{
        if (nr_cpus_node(node)) {
                cpumask_t mask = node_to_cpumask(node);

                if (cpus_intersects(mask, ctx->cpus_allowed))
                        return 1;
        }

        return 0;
}

static int node_allowed(struct spu_context *ctx, int node)
{
        int rval;

        spin_lock(&spu_prio->runq_lock);
        rval = __node_allowed(ctx, node);
        spin_unlock(&spu_prio->runq_lock);

        return rval;
}

void do_notify_spus_active(void)
{
        int node;

        /*
         * Wake up the active spu_contexts.
         *
         * When the awakened processes see their "notify_active" flag is set,
         * they will call spu_switch_notify().
         */
        for_each_online_node(node) {
                struct spu *spu;

                mutex_lock(&cbe_spu_info[node].list_mutex);
                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list) {
                        if (spu->alloc_state != SPU_FREE) {
                                struct spu_context *ctx = spu->ctx;
                                set_bit(SPU_SCHED_NOTIFY_ACTIVE,
                                        &ctx->sched_flags);
                                mb();
                                wake_up_all(&ctx->stop_wq);
                        }
                }
                mutex_unlock(&cbe_spu_info[node].list_mutex);
        }
}

/**
 * spu_bind_context - bind spu context to physical spu
 * @spu:        physical spu to bind to
 * @ctx:        context to bind
 */
static void spu_bind_context(struct spu *spu, struct spu_context *ctx)
{
        spu_context_trace(spu_bind_context__enter, ctx, spu);

        spuctx_switch_state(ctx, SPU_UTIL_SYSTEM);

        if (ctx->flags & SPU_CREATE_NOSCHED)
                atomic_inc(&cbe_spu_info[spu->node].reserved_spus);

        ctx->stats.slb_flt_base = spu->stats.slb_flt;
        ctx->stats.class2_intr_base = spu->stats.class2_intr;

        spu_associate_mm(spu, ctx->owner);

        spin_lock_irq(&spu->register_lock);
        spu->ctx = ctx;
        spu->flags = 0;
        ctx->spu = spu;
        ctx->ops = &spu_hw_ops;
        spu->pid = current->pid;
        spu->tgid = current->tgid;
        spu->ibox_callback = spufs_ibox_callback;
        spu->wbox_callback = spufs_wbox_callback;
        spu->stop_callback = spufs_stop_callback;
        spu->mfc_callback = spufs_mfc_callback;
        spin_unlock_irq(&spu->register_lock);

        spu_unmap_mappings(ctx);

        spu_switch_log_notify(spu, ctx, SWITCH_LOG_START, 0);
        spu_restore(&ctx->csa, spu);
        spu->timestamp = jiffies;
        spu_switch_notify(spu, ctx);
        ctx->state = SPU_STATE_RUNNABLE;

        spuctx_switch_state(ctx, SPU_UTIL_USER);
}

/*
 * Must be used with the list_mutex held.
 */
static inline int sched_spu(struct spu *spu)
{
        BUG_ON(!mutex_is_locked(&cbe_spu_info[spu->node].list_mutex));

        return (!spu->ctx || !(spu->ctx->flags & SPU_CREATE_NOSCHED));
}

static void aff_merge_remaining_ctxs(struct spu_gang *gang)
{
        struct spu_context *ctx;

        list_for_each_entry(ctx, &gang->aff_list_head, aff_list) {
                if (list_empty(&ctx->aff_list))
                        list_add(&ctx->aff_list, &gang->aff_list_head);
        }
        gang->aff_flags |= AFF_MERGED;
}

static void aff_set_offsets(struct spu_gang *gang)
{
        struct spu_context *ctx;
        int offset;

        offset = -1;
        list_for_each_entry_reverse(ctx, &gang->aff_ref_ctx->aff_list,
                                                                aff_list) {
                if (&ctx->aff_list == &gang->aff_list_head)
                        break;
                ctx->aff_offset = offset--;
        }

        offset = 0;
        list_for_each_entry(ctx, gang->aff_ref_ctx->aff_list.prev, aff_list) {
                if (&ctx->aff_list == &gang->aff_list_head)
                        break;
                ctx->aff_offset = offset++;
        }

        gang->aff_flags |= AFF_OFFSETS_SET;
}

static struct spu *aff_ref_location(struct spu_context *ctx, int mem_aff,
                 int group_size, int lowest_offset)
{
        struct spu *spu;
        int node, n;

        /*
         * TODO: A better algorithm could be used to find a good spu to be
         *       used as reference location for the ctxs chain.
         */
        node = cpu_to_node(raw_smp_processor_id());
        for (n = 0; n < MAX_NUMNODES; n++, node++) {
                int available_spus;

                node = (node < MAX_NUMNODES) ? node : 0;
                if (!node_allowed(ctx, node))
                        continue;

                available_spus = 0;
                mutex_lock(&cbe_spu_info[node].list_mutex);
                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list) {
                        if (spu->ctx && spu->ctx->gang
                                        && spu->ctx->aff_offset == 0)
                                available_spus -=
                                        (spu->ctx->gang->contexts - 1);
                        else
                                available_spus++;
                }
                if (available_spus < ctx->gang->contexts) {
                        mutex_unlock(&cbe_spu_info[node].list_mutex);
                        continue;
                }

                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list) {
                        if ((!mem_aff || spu->has_mem_affinity) &&
                                                        sched_spu(spu)) {
                                mutex_unlock(&cbe_spu_info[node].list_mutex);
                                return spu;
                        }
                }
                mutex_unlock(&cbe_spu_info[node].list_mutex);
        }
        return NULL;
}

static void aff_set_ref_point_location(struct spu_gang *gang)
{
        int mem_aff, gs, lowest_offset;
        struct spu_context *ctx;
        struct spu *tmp;

        mem_aff = gang->aff_ref_ctx->flags & SPU_CREATE_AFFINITY_MEM;
        lowest_offset = 0;
        gs = 0;

        list_for_each_entry(tmp, &gang->aff_list_head, aff_list)
                gs++;

        list_for_each_entry_reverse(ctx, &gang->aff_ref_ctx->aff_list,
                                                                aff_list) {
                if (&ctx->aff_list == &gang->aff_list_head)
                        break;
                lowest_offset = ctx->aff_offset;
        }

        gang->aff_ref_spu = aff_ref_location(gang->aff_ref_ctx, mem_aff, gs,
                                                        lowest_offset);
}

static struct spu *ctx_location(struct spu *ref, int offset, int node)
{
        struct spu *spu;

        spu = NULL;
        if (offset >= 0) {
                list_for_each_entry(spu, ref->aff_list.prev, aff_list) {
                        BUG_ON(spu->node != node);
                        if (offset == 0)
                                break;
                        if (sched_spu(spu))
                                offset--;
                }
        } else {
                list_for_each_entry_reverse(spu, ref->aff_list.next, aff_list) {
                        BUG_ON(spu->node != node);
                        if (offset == 0)
                                break;
                        if (sched_spu(spu))
                                offset++;
                }
        }

        return spu;
}

/*
 * affinity_check is called each time a context is going to be scheduled.
 * It returns the spu ptr on which the context must run.
 */
static int has_affinity(struct spu_context *ctx)
{
        struct spu_gang *gang = ctx->gang;

        if (list_empty(&ctx->aff_list))
                return 0;

        if (atomic_read(&ctx->gang->aff_sched_count) == 0)
                ctx->gang->aff_ref_spu = NULL;

        if (!gang->aff_ref_spu) {
                if (!(gang->aff_flags & AFF_MERGED))
                        aff_merge_remaining_ctxs(gang);
                if (!(gang->aff_flags & AFF_OFFSETS_SET))
                        aff_set_offsets(gang);
                aff_set_ref_point_location(gang);
        }

        return gang->aff_ref_spu != NULL;
}

/**
 * spu_unbind_context - unbind spu context from physical spu
 * @spu:        physical spu to unbind from
 * @ctx:        context to unbind
 */
static void spu_unbind_context(struct spu *spu, struct spu_context *ctx)
{
        u32 status;

        spu_context_trace(spu_unbind_context__enter, ctx, spu);

        spuctx_switch_state(ctx, SPU_UTIL_SYSTEM);

        if (spu->ctx->flags & SPU_CREATE_NOSCHED)
                atomic_dec(&cbe_spu_info[spu->node].reserved_spus);

        if (ctx->gang)
                atomic_dec_if_positive(&ctx->gang->aff_sched_count);

        spu_switch_notify(spu, NULL);
        spu_unmap_mappings(ctx);
        spu_save(&ctx->csa, spu);
        spu_switch_log_notify(spu, ctx, SWITCH_LOG_STOP, 0);

        spin_lock_irq(&spu->register_lock);
        spu->timestamp = jiffies;
        ctx->state = SPU_STATE_SAVED;
        spu->ibox_callback = NULL;
        spu->wbox_callback = NULL;
        spu->stop_callback = NULL;
        spu->mfc_callback = NULL;
        spu->pid = 0;
        spu->tgid = 0;
        ctx->ops = &spu_backing_ops;
        spu->flags = 0;
        spu->ctx = NULL;
        spin_unlock_irq(&spu->register_lock);

        spu_associate_mm(spu, NULL);

        ctx->stats.slb_flt +=
                (spu->stats.slb_flt - ctx->stats.slb_flt_base);
        ctx->stats.class2_intr +=
                (spu->stats.class2_intr - ctx->stats.class2_intr_base);

        /* This maps the underlying spu state to idle */
        spuctx_switch_state(ctx, SPU_UTIL_IDLE_LOADED);
        ctx->spu = NULL;

        if (spu_stopped(ctx, &status))
                wake_up_all(&ctx->stop_wq);
}

/**
 * spu_add_to_rq - add a context to the runqueue
 * @ctx:       context to add
 */
static void __spu_add_to_rq(struct spu_context *ctx)
{
        /*
         * Unfortunately this code path can be called from multiple threads
         * on behalf of a single context due to the way the problem state
         * mmap support works.
         *
         * Fortunately we need to wake up all these threads at the same time
         * and can simply skip the runqueue addition for every but the first
         * thread getting into this codepath.
         *
         * It's still quite hacky, and long-term we should proxy all other
         * threads through the owner thread so that spu_run is in control
         * of all the scheduling activity for a given context.
         */
        if (list_empty(&ctx->rq)) {
                list_add_tail(&ctx->rq, &spu_prio->runq[ctx->prio]);
                set_bit(ctx->prio, spu_prio->bitmap);
                if (!spu_prio->nr_waiting++)
                        __mod_timer(&spusched_timer, jiffies + SPUSCHED_TICK);
        }
}

static void spu_add_to_rq(struct spu_context *ctx)
{
        spin_lock(&spu_prio->runq_lock);
        __spu_add_to_rq(ctx);
        spin_unlock(&spu_prio->runq_lock);
}

static void __spu_del_from_rq(struct spu_context *ctx)
{
        int prio = ctx->prio;

        if (!list_empty(&ctx->rq)) {
                if (!--spu_prio->nr_waiting)
                        del_timer(&spusched_timer);
                list_del_init(&ctx->rq);

                if (list_empty(&spu_prio->runq[prio]))
                        clear_bit(prio, spu_prio->bitmap);
        }
}

void spu_del_from_rq(struct spu_context *ctx)
{
        spin_lock(&spu_prio->runq_lock);
        __spu_del_from_rq(ctx);
        spin_unlock(&spu_prio->runq_lock);
}

static void spu_prio_wait(struct spu_context *ctx)
{
        DEFINE_WAIT(wait);

        /*
         * The caller must explicitly wait for a context to be loaded
         * if the nosched flag is set.  If NOSCHED is not set, the caller
         * queues the context and waits for an spu event or error.
         */
        BUG_ON(!(ctx->flags & SPU_CREATE_NOSCHED));

        spin_lock(&spu_prio->runq_lock);
        prepare_to_wait_exclusive(&ctx->stop_wq, &wait, TASK_INTERRUPTIBLE);
        if (!signal_pending(current)) {
                __spu_add_to_rq(ctx);
                spin_unlock(&spu_prio->runq_lock);
                mutex_unlock(&ctx->state_mutex);
                schedule();
                mutex_lock(&ctx->state_mutex);
                spin_lock(&spu_prio->runq_lock);
                __spu_del_from_rq(ctx);
        }
        spin_unlock(&spu_prio->runq_lock);
        __set_current_state(TASK_RUNNING);
        remove_wait_queue(&ctx->stop_wq, &wait);
}

static struct spu *spu_get_idle(struct spu_context *ctx)
{
        struct spu *spu, *aff_ref_spu;
        int node, n;

        spu_context_nospu_trace(spu_get_idle__enter, ctx);

        if (ctx->gang) {
                mutex_lock(&ctx->gang->aff_mutex);
                if (has_affinity(ctx)) {
                        aff_ref_spu = ctx->gang->aff_ref_spu;
                        atomic_inc(&ctx->gang->aff_sched_count);
                        mutex_unlock(&ctx->gang->aff_mutex);
                        node = aff_ref_spu->node;

                        mutex_lock(&cbe_spu_info[node].list_mutex);
                        spu = ctx_location(aff_ref_spu, ctx->aff_offset, node);
                        if (spu && spu->alloc_state == SPU_FREE)
                                goto found;
                        mutex_unlock(&cbe_spu_info[node].list_mutex);

                        atomic_dec(&ctx->gang->aff_sched_count);
                        goto not_found;
                }
                mutex_unlock(&ctx->gang->aff_mutex);
        }
        node = cpu_to_node(raw_smp_processor_id());
        for (n = 0; n < MAX_NUMNODES; n++, node++) {
                node = (node < MAX_NUMNODES) ? node : 0;
                if (!node_allowed(ctx, node))
                        continue;

                mutex_lock(&cbe_spu_info[node].list_mutex);
                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list) {
                        if (spu->alloc_state == SPU_FREE)
                                goto found;
                }
                mutex_unlock(&cbe_spu_info[node].list_mutex);
        }

 not_found:
        spu_context_nospu_trace(spu_get_idle__not_found, ctx);
        return NULL;

 found:
        spu->alloc_state = SPU_USED;
        mutex_unlock(&cbe_spu_info[node].list_mutex);
        spu_context_trace(spu_get_idle__found, ctx, spu);
        spu_init_channels(spu);
        return spu;
}

/**
 * find_victim - find a lower priority context to preempt
 * @ctx:        canidate context for running
 *
 * Returns the freed physical spu to run the new context on.
 */
static struct spu *find_victim(struct spu_context *ctx)
{
        struct spu_context *victim = NULL;
        struct spu *spu;
        int node, n;

        spu_context_nospu_trace(spu_find_victim__enter, ctx);

        /*
         * Look for a possible preemption candidate on the local node first.
         * If there is no candidate look at the other nodes.  This isn't
         * exactly fair, but so far the whole spu scheduler tries to keep
         * a strong node affinity.  We might want to fine-tune this in
         * the future.
         */
 restart:
        node = cpu_to_node(raw_smp_processor_id());
        for (n = 0; n < MAX_NUMNODES; n++, node++) {
                node = (node < MAX_NUMNODES) ? node : 0;
                if (!node_allowed(ctx, node))
                        continue;

                mutex_lock(&cbe_spu_info[node].list_mutex);
                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list) {
                        struct spu_context *tmp = spu->ctx;

                        if (tmp && tmp->prio > ctx->prio &&
                            !(tmp->flags & SPU_CREATE_NOSCHED) &&
                            (!victim || tmp->prio > victim->prio)) {
                                victim = spu->ctx;
                        }
                }
                if (victim)
                        get_spu_context(victim);
                mutex_unlock(&cbe_spu_info[node].list_mutex);

                if (victim) {
                        /*
                         * This nests ctx->state_mutex, but we always lock
                         * higher priority contexts before lower priority
                         * ones, so this is safe until we introduce
                         * priority inheritance schemes.
                         *
                         * XXX if the highest priority context is locked,
                         * this can loop a long time.  Might be better to
                         * look at another context or give up after X retries.
                         */
                        if (!mutex_trylock(&victim->state_mutex)) {
                                put_spu_context(victim);
                                victim = NULL;
                                goto restart;
                        }

                        spu = victim->spu;
                        if (!spu || victim->prio <= ctx->prio) {
                                /*
                                 * This race can happen because we've dropped
                                 * the active list mutex.  Not a problem, just
                                 * restart the search.
                                 */
                                mutex_unlock(&victim->state_mutex);
                                put_spu_context(victim);
                                victim = NULL;
                                goto restart;
                        }

                        spu_context_trace(__spu_deactivate__unload, ctx, spu);

                        mutex_lock(&cbe_spu_info[node].list_mutex);
                        cbe_spu_info[node].nr_active--;
                        spu_unbind_context(spu, victim);
                        mutex_unlock(&cbe_spu_info[node].list_mutex);

                        victim->stats.invol_ctx_switch++;
                        spu->stats.invol_ctx_switch++;
                        if (test_bit(SPU_SCHED_SPU_RUN, &victim->sched_flags))
                                spu_add_to_rq(victim);

                        mutex_unlock(&victim->state_mutex);
                        put_spu_context(victim);

                        return spu;
                }
        }

        return NULL;
}

static void __spu_schedule(struct spu *spu, struct spu_context *ctx)
{
        int node = spu->node;
        int success = 0;

        spu_set_timeslice(ctx);

        mutex_lock(&cbe_spu_info[node].list_mutex);
        if (spu->ctx == NULL) {
                spu_bind_context(spu, ctx);
                cbe_spu_info[node].nr_active++;
                spu->alloc_state = SPU_USED;
                success = 1;
        }
        mutex_unlock(&cbe_spu_info[node].list_mutex);

        if (success)
                wake_up_all(&ctx->run_wq);
        else
                spu_add_to_rq(ctx);
}

static void spu_schedule(struct spu *spu, struct spu_context *ctx)
{
        /* not a candidate for interruptible because it's called either
           from the scheduler thread or from spu_deactivate */
        mutex_lock(&ctx->state_mutex);
        __spu_schedule(spu, ctx);
        spu_release(ctx);
}

static void spu_unschedule(struct spu *spu, struct spu_context *ctx)
{
        int node = spu->node;

        mutex_lock(&cbe_spu_info[node].list_mutex);
        cbe_spu_info[node].nr_active--;
        spu->alloc_state = SPU_FREE;
        spu_unbind_context(spu, ctx);
        ctx->stats.invol_ctx_switch++;
        spu->stats.invol_ctx_switch++;
        mutex_unlock(&cbe_spu_info[node].list_mutex);
}

/**
 * spu_activate - find a free spu for a context and execute it
 * @ctx:        spu context to schedule
 * @flags:      flags (currently ignored)
 *
 * Tries to find a free spu to run @ctx.  If no free spu is available
 * add the context to the runqueue so it gets woken up once an spu
 * is available.
 */
int spu_activate(struct spu_context *ctx, unsigned long flags)
{
        struct spu *spu;

        /*
         * If there are multiple threads waiting for a single context
         * only one actually binds the context while the others will
         * only be able to acquire the state_mutex once the context
         * already is in runnable state.
         */
        if (ctx->spu)
                return 0;

spu_activate_top:
        if (signal_pending(current))
                return -ERESTARTSYS;

        spu = spu_get_idle(ctx);
        /*
         * If this is a realtime thread we try to get it running by
         * preempting a lower priority thread.
         */
        if (!spu && rt_prio(ctx->prio))
                spu = find_victim(ctx);
        if (spu) {
                unsigned long runcntl;

                runcntl = ctx->ops->runcntl_read(ctx);
                __spu_schedule(spu, ctx);
                if (runcntl & SPU_RUNCNTL_RUNNABLE)
                        spuctx_switch_state(ctx, SPU_UTIL_USER);

                return 0;
        }

        if (ctx->flags & SPU_CREATE_NOSCHED) {
                spu_prio_wait(ctx);
                goto spu_activate_top;
        }

        spu_add_to_rq(ctx);

        return 0;
}

/**
 * grab_runnable_context - try to find a runnable context
 *
 * Remove the highest priority context on the runqueue and return it
 * to the caller.  Returns %NULL if no runnable context was found.
 */
static struct spu_context *grab_runnable_context(int prio, int node)
{
        struct spu_context *ctx;
        int best;

        spin_lock(&spu_prio->runq_lock);
        best = find_first_bit(spu_prio->bitmap, prio);
        while (best < prio) {
                struct list_head *rq = &spu_prio->runq[best];

                list_for_each_entry(ctx, rq, rq) {
                        /* XXX(hch): check for affinity here aswell */
                        if (__node_allowed(ctx, node)) {
                                __spu_del_from_rq(ctx);
                                goto found;
                        }
                }
                best++;
        }
        ctx = NULL;
 found:
        spin_unlock(&spu_prio->runq_lock);
        return ctx;
}

static int __spu_deactivate(struct spu_context *ctx, int force, int max_prio)
{
        struct spu *spu = ctx->spu;
        struct spu_context *new = NULL;

        if (spu) {
                new = grab_runnable_context(max_prio, spu->node);
                if (new || force) {
                        spu_unschedule(spu, ctx);
                        if (new) {
                                if (new->flags & SPU_CREATE_NOSCHED)
                                        wake_up(&new->stop_wq);
                                else {
                                        spu_release(ctx);
                                        spu_schedule(spu, new);
                                        /* this one can't easily be made
                                           interruptible */
                                        mutex_lock(&ctx->state_mutex);
                                }
                        }
                }
        }

        return new != NULL;
}

/**
 * spu_deactivate - unbind a context from it's physical spu
 * @ctx:        spu context to unbind
 *
 * Unbind @ctx from the physical spu it is running on and schedule
 * the highest priority context to run on the freed physical spu.
 */
void spu_deactivate(struct spu_context *ctx)
{
        spu_context_nospu_trace(spu_deactivate__enter, ctx);
        __spu_deactivate(ctx, 1, MAX_PRIO);
}

/**
 * spu_yield -  yield a physical spu if others are waiting
 * @ctx:        spu context to yield
 *
 * Check if there is a higher priority context waiting and if yes
 * unbind @ctx from the physical spu and schedule the highest
 * priority context to run on the freed physical spu instead.
 */
void spu_yield(struct spu_context *ctx)
{
        spu_context_nospu_trace(spu_yield__enter, ctx);
        if (!(ctx->flags & SPU_CREATE_NOSCHED)) {
                mutex_lock(&ctx->state_mutex);
                __spu_deactivate(ctx, 0, MAX_PRIO);
                mutex_unlock(&ctx->state_mutex);
        }
}

static noinline void spusched_tick(struct spu_context *ctx)
{
        struct spu_context *new = NULL;
        struct spu *spu = NULL;

        if (spu_acquire(ctx))
                BUG();  /* a kernel thread never has signals pending */

        if (ctx->state != SPU_STATE_RUNNABLE)
                goto out;
        if (ctx->flags & SPU_CREATE_NOSCHED)
                goto out;
        if (ctx->policy == SCHED_FIFO)
                goto out;

        if (--ctx->time_slice && test_bit(SPU_SCHED_SPU_RUN, &ctx->sched_flags))
                goto out;

        spu = ctx->spu;

        spu_context_trace(spusched_tick__preempt, ctx, spu);

        new = grab_runnable_context(ctx->prio + 1, spu->node);
        if (new) {
                spu_unschedule(spu, ctx);
                if (test_bit(SPU_SCHED_SPU_RUN, &ctx->sched_flags))
                        spu_add_to_rq(ctx);
        } else {
                spu_context_nospu_trace(spusched_tick__newslice, ctx);
                if (!ctx->time_slice)
                        ctx->time_slice++;
        }
out:
        spu_release(ctx);

        if (new)
                spu_schedule(spu, new);
}

/**
 * count_active_contexts - count nr of active tasks
 *
 * Return the number of tasks currently running or waiting to run.
 *
 * Note that we don't take runq_lock / list_mutex here.  Reading
 * a single 32bit value is atomic on powerpc, and we don't care
 * about memory ordering issues here.
 */
static unsigned long count_active_contexts(void)
{
        int nr_active = 0, node;

        for (node = 0; node < MAX_NUMNODES; node++)
                nr_active += cbe_spu_info[node].nr_active;
        nr_active += spu_prio->nr_waiting;

        return nr_active;
}

/**
 * spu_calc_load - update the avenrun load estimates.
 *
 * No locking against reading these values from userspace, as for
 * the CPU loadavg code.
 */
static void spu_calc_load(void)
{
        unsigned long active_tasks; /* fixed-point */

        active_tasks = count_active_contexts() * FIXED_1;
        CALC_LOAD(spu_avenrun[0], EXP_1, active_tasks);
        CALC_LOAD(spu_avenrun[1], EXP_5, active_tasks);
        CALC_LOAD(spu_avenrun[2], EXP_15, active_tasks);
}

static void spusched_wake(unsigned long data)
{
        mod_timer(&spusched_timer, jiffies + SPUSCHED_TICK);
        wake_up_process(spusched_task);
}

static void spuloadavg_wake(unsigned long data)
{
        mod_timer(&spuloadavg_timer, jiffies + LOAD_FREQ);
        spu_calc_load();
}

static int spusched_thread(void *unused)
{
        struct spu *spu;
        int node;

        while (!kthread_should_stop()) {
                set_current_state(TASK_INTERRUPTIBLE);
                schedule();
                for (node = 0; node < MAX_NUMNODES; node++) {
                        struct mutex *mtx = &cbe_spu_info[node].list_mutex;

                        mutex_lock(mtx);
                        list_for_each_entry(spu, &cbe_spu_info[node].spus,
                                        cbe_list) {
                                struct spu_context *ctx = spu->ctx;

                                if (ctx) {
                                        get_spu_context(ctx);
                                        mutex_unlock(mtx);
                                        spusched_tick(ctx);
                                        mutex_lock(mtx);
                                        put_spu_context(ctx);
                                }
                        }
                        mutex_unlock(mtx);
                }
        }

        return 0;
}

void spuctx_switch_state(struct spu_context *ctx,
                enum spu_utilization_state new_state)
{
        unsigned long long curtime;
        signed long long delta;
        struct timespec ts;
        struct spu *spu;
        enum spu_utilization_state old_state;
        int node;

        ktime_get_ts(&ts);
        curtime = timespec_to_ns(&ts);
        delta = curtime - ctx->stats.tstamp;

        WARN_ON(!mutex_is_locked(&ctx->state_mutex));
        WARN_ON(delta < 0);

        spu = ctx->spu;
        old_state = ctx->stats.util_state;
        ctx->stats.util_state = new_state;
        ctx->stats.tstamp = curtime;

        /*
         * Update the physical SPU utilization statistics.
         */
        if (spu) {
                ctx->stats.times[old_state] += delta;
                spu->stats.times[old_state] += delta;
                spu->stats.util_state = new_state;
                spu->stats.tstamp = curtime;
                node = spu->node;
                if (old_state == SPU_UTIL_USER)
                        atomic_dec(&cbe_spu_info[node].busy_spus);
                if (new_state == SPU_UTIL_USER)
                        atomic_inc(&cbe_spu_info[node].busy_spus);
        }
}

#define LOAD_INT(x) ((x) >> FSHIFT)
#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)

static int show_spu_loadavg(struct seq_file *s, void *private)
{
        int a, b, c;

        a = spu_avenrun[0] + (FIXED_1/200);
        b = spu_avenrun[1] + (FIXED_1/200);
        c = spu_avenrun[2] + (FIXED_1/200);

        /*
         * Note that last_pid doesn't really make much sense for the
         * SPU loadavg (it even seems very odd on the CPU side...),
         * but we include it here to have a 100% compatible interface.
         */
        seq_printf(s, "%d.%02d %d.%02d %d.%02d %ld/%d %d\n",
                LOAD_INT(a), LOAD_FRAC(a),
                LOAD_INT(b), LOAD_FRAC(b),
                LOAD_INT(c), LOAD_FRAC(c),
                count_active_contexts(),
                atomic_read(&nr_spu_contexts),
                current->nsproxy->pid_ns->last_pid);
        return 0;
}

static int spu_loadavg_open(struct inode *inode, struct file *file)
{
        return single_open(file, show_spu_loadavg, NULL);
}

static const struct file_operations spu_loadavg_fops = {
        .open           = spu_loadavg_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

int __init spu_sched_init(void)
{
        struct proc_dir_entry *entry;
        int err = -ENOMEM, i;

        spu_prio = kzalloc(sizeof(struct spu_prio_array), GFP_KERNEL);
        if (!spu_prio)
                goto out;

        for (i = 0; i < MAX_PRIO; i++) {
                INIT_LIST_HEAD(&spu_prio->runq[i]);
                __clear_bit(i, spu_prio->bitmap);
        }
        spin_lock_init(&spu_prio->runq_lock);

        setup_timer(&spusched_timer, spusched_wake, 0);
        setup_timer(&spuloadavg_timer, spuloadavg_wake, 0);

        spusched_task = kthread_run(spusched_thread, NULL, "spusched");
        if (IS_ERR(spusched_task)) {
                err = PTR_ERR(spusched_task);
                goto out_free_spu_prio;
        }

        mod_timer(&spuloadavg_timer, 0);

        entry = proc_create("spu_loadavg", 0, NULL, &spu_loadavg_fops);
        if (!entry)
                goto out_stop_kthread;

        pr_debug("spusched: tick: %d, min ticks: %d, default ticks: %d\n",
                        SPUSCHED_TICK, MIN_SPU_TIMESLICE, DEF_SPU_TIMESLICE);
        return 0;

 out_stop_kthread:
        kthread_stop(spusched_task);
 out_free_spu_prio:
        kfree(spu_prio);
 out:
        return err;
}

void spu_sched_exit(void)
{
        struct spu *spu;
        int node;

        remove_proc_entry("spu_loadavg", NULL);

        del_timer_sync(&spusched_timer);
        del_timer_sync(&spuloadavg_timer);
        kthread_stop(spusched_task);

        for (node = 0; node < MAX_NUMNODES; node++) {
                mutex_lock(&cbe_spu_info[node].list_mutex);
                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list)
                        if (spu->alloc_state != SPU_FREE)
                                spu->alloc_state = SPU_FREE;
                mutex_unlock(&cbe_spu_info[node].list_mutex);
        }
        kfree(spu_prio);
}