sched.c

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/* sched.c - SPU scheduler.
 *
 * Copyright (C) IBM 2005
 * Author: Mark Nutter <[email protected]>
 *
 * 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/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/slab.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 <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"
#define CREATE_TRACE_POINTS
#include "sputrace.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.
     */
    cpumask_copy(&ctx->cpus_allowed, tsk_cpus_allowed(current));

    /* 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)) {
        const struct cpumask *mask = cpumask_of_node(node);

        if (cpumask_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);
    }
}

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++) {
        /*
         * "available_spus" counts how many spus are not potentially
         * going to be used by other affinity gangs whose reference
         * context is already in place. Although this code seeks to
         * avoid having affinity gangs with a summed amount of
         * contexts bigger than the amount of spus in the node,
         * this may happen sporadically. In this case, available_spus
         * becomes negative, which is harmless.
         */
        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
                    && spu->ctx->gang->aff_ref_spu)
                available_spus -= spu->ctx->gang->contexts;
            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;
}

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)
        /*
         * If ctx->gang->aff_sched_count is positive, SPU affinity is
         * being considered in this gang. Using atomic_dec_if_positive
         * allow us to skip an explicit check for affinity in this 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);
}

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;
}

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);
    if (ctx->state == SPU_STATE_SAVED)
        __spu_schedule(spu, ctx);
    spu_release(ctx);
}

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

    mutex_lock(&cbe_spu_info[node].list_mutex);
    cbe_spu_info[node].nr_active--;
    if (free_spu)
        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);
}

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;
}

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 as well */
            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, new == NULL);
            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;
}

void spu_deactivate(struct spu_context *ctx)
{
    spu_context_nospu_trace(spu_deactivate__enter, ctx);
    __spu_deactivate(ctx, 1, MAX_PRIO);
}

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, 0);
        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);
}

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;
}

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);
}