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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 <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;

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

      /*
       * We do our own priority calculations, so we normally want
       * ->static_prio to start with. Unfortunately thies 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;

      /*
       * A lot of places that don't hold list_mutex poke into
       * cpus_allowed, including grab_runnable_context which
       * already holds the runq_lock.  So abuse runq_lock
       * to protect this field aswell.
       */
      spin_lock(&spu_prio->runq_lock);
      ctx->cpus_allowed = current->cpus_allowed;
      spin_unlock(&spu_prio->runq_lock);
}

void spu_update_sched_info(struct spu_context *ctx)
{
      int node = ctx->spu->node;

      mutex_lock(&cbe_spu_info[node].list_mutex);
      __spu_update_sched_info(ctx);
      mutex_unlock(&cbe_spu_info[node].list_mutex);
}

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)
{
      pr_debug("%s: pid=%d SPU=%d NODE=%d\n", __FUNCTION__, current->pid,
             spu->number, spu->node);
      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->ctx = ctx;
      spu->flags = 0;
      ctx->spu = spu;
      ctx->ops = &spu_hw_ops;
      spu->pid = current->pid;
      spu->tgid = current->tgid;
      spu_associate_mm(spu, ctx->owner);
      spu->ibox_callback = spufs_ibox_callback;
      spu->wbox_callback = spufs_wbox_callback;
      spu->stop_callback = spufs_stop_callback;
      spu->mfc_callback = spufs_mfc_callback;
      spu->dma_callback = spufs_dma_callback;
      mb();
      spu_unmap_mappings(ctx);
      spu_restore(&ctx->csa, spu);
      spu->timestamp = jiffies;
      spu_cpu_affinity_set(spu, raw_smp_processor_id());
      spu_switch_notify(spu, ctx);
      ctx->state = SPU_STATE_RUNNABLE;

      spuctx_switch_state(ctx, SPU_UTIL_IDLE_LOADED);
}

/*
 * 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++) {
            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 ((!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 (!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)
{
      pr_debug("%s: unbind pid=%d SPU=%d NODE=%d\n", __FUNCTION__,
             spu->pid, spu->number, spu->node);
      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){
            mutex_lock(&ctx->gang->aff_mutex);
            if (has_affinity(ctx)) {
                  if (atomic_dec_and_test(&ctx->gang->aff_sched_count))
                        ctx->gang->aff_ref_spu = NULL;
            }
            mutex_unlock(&ctx->gang->aff_mutex);
      }

      spu_switch_notify(spu, NULL);
      spu_unmap_mappings(ctx);
      spu_save(&ctx->csa, spu);
      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->dma_callback = NULL;
      spu_associate_mm(spu, NULL);
      spu->pid = 0;
      spu->tgid = 0;
      ctx->ops = &spu_backing_ops;
      spu->flags = 0;
      spu->ctx = 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;
}

/**
 * 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_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);
      }
}

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

      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;

      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);

                  mutex_lock(&ctx->gang->aff_mutex);
                  if (atomic_dec_and_test(&ctx->gang->aff_sched_count))
                        ctx->gang->aff_ref_spu = NULL;
                  mutex_unlock(&ctx->gang->aff_mutex);

                  return NULL;
            }
            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);
      }

      return NULL;

 found:
      spu->alloc_state = SPU_USED;
      mutex_unlock(&cbe_spu_info[node].list_mutex);
      pr_debug("Got SPU %d %d\n", spu->number, spu->node);
      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;

      /*
       * 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 schedule 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 &&
                      (!victim || tmp->prio > victim->prio))
                        victim = spu->ctx;
            }
            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.
                   */
                  if (!mutex_trylock(&victim->state_mutex)) {
                        victim = NULL;
                        goto restart;
                  }

                  spu = victim->spu;
                  if (!spu) {
                        /*
                         * This race can happen because we've dropped
                         * the active list mutex.  No a problem, just
                         * restart the search.
                         */
                        mutex_unlock(&victim->state_mutex);
                        victim = NULL;
                        goto restart;
                  }

                  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++;
                  mutex_unlock(&victim->state_mutex);
                  /*
                   * We need to break out of the wait loop in spu_run
                   * manually to ensure this context gets put on the
                   * runqueue again ASAP.
                   */
                  wake_up(&victim->stop_wq);
                  return spu;
            }
      }

      return NULL;
}

/**
 * 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)
{
      do {
            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 = 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) {
                  int node = spu->node;

                  mutex_lock(&cbe_spu_info[node].list_mutex);
                  spu_bind_context(spu, ctx);
                  cbe_spu_info[node].nr_active++;
                  mutex_unlock(&cbe_spu_info[node].list_mutex);
                  return 0;
            }

            spu_prio_wait(ctx);
      } while (!signal_pending(current));

      return -ERESTARTSYS;
}

/**
 * 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) {
                  int node = spu->node;

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

                  ctx->stats.vol_ctx_switch++;
                  spu->stats.vol_ctx_switch++;

                  if (new)
                        wake_up(&new->stop_wq);
            }

      }

      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_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)
{
      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)
{
      if (ctx->flags & SPU_CREATE_NOSCHED)
            return;
      if (ctx->policy == SCHED_FIFO)
            return;

      if (--ctx->time_slice)
            return;

      /*
       * Unfortunately list_mutex ranks outside of state_mutex, so
       * we have to trylock here.  If we fail give the context another
       * tick and try again.
       */
      if (mutex_trylock(&ctx->state_mutex)) {
            struct spu *spu = ctx->spu;
            struct spu_context *new;

            new = grab_runnable_context(ctx->prio + 1, spu->node);
            if (new) {
                  spu_unbind_context(spu, ctx);
                  ctx->stats.invol_ctx_switch++;
                  spu->stats.invol_ctx_switch++;
                  spu->alloc_state = SPU_FREE;
                  cbe_spu_info[spu->node].nr_active--;
                  wake_up(&new->stop_wq);
                  /*
                   * We need to break out of the wait loop in
                   * spu_run manually to ensure this context
                   * gets put on the runqueue again ASAP.
                   */
                  wake_up(&ctx->stop_wq);
            }
            spu_set_timeslice(ctx);
            mutex_unlock(&ctx->state_mutex);
      } else {
            ctx->time_slice++;
      }
}

/**
 * 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 - given tick count, update the avenrun load estimates.
 * @tick:   tick count
 *
 * No locking against reading these values from userspace, as for
 * the CPU loadavg code.
 */
static void spu_calc_load(unsigned long ticks)
{
      unsigned long active_tasks; /* fixed-point */
      static int count = LOAD_FREQ;

      count -= ticks;

      if (unlikely(count < 0)) {
            active_tasks = count_active_contexts() * FIXED_1;
            do {
                  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);
                  count += LOAD_FREQ;
            } while (count < 0);
      }
}

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

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++) {
                  mutex_lock(&cbe_spu_info[node].list_mutex);
                  list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list)
                        if (spu->ctx)
                              spusched_tick(spu->ctx);
                  mutex_unlock(&cbe_spu_info[node].list_mutex);
            }
      }

      return 0;
}

#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);

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

      entry = create_proc_entry("spu_loadavg", 0, NULL);
      if (!entry)
            goto out_stop_kthread;
      entry->proc_fops = &spu_loadavg_fops;

      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);
      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);
}

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