[PATCH] spufs: Improved SPU preemptability.
This patch makes it easier to preempt an SPU context by
having the scheduler hold ctx->state_sema for much shorter
periods of time.
As part of this restructuring, the control logic for the "run"
operation is moved from arch/ppc64/kernel/spu_base.c to
fs/spufs/file.c. Of course the base retains "bottom half"
handlers for class{0,1} irqs. The new run loop will re-acquire
an SPU if preempted.
From: Mark Nutter <mnutter@us.ibm.com>
Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 5750270..e2f10b5 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -119,7 +119,8 @@
}
}
-static void prio_wait(struct spu_runqueue *rq, u64 flags)
+static void prio_wait(struct spu_runqueue *rq, struct spu_context *ctx,
+ u64 flags)
{
int prio = current->prio;
wait_queue_head_t *wq = &rq->prio.waitq[prio];
@@ -130,9 +131,11 @@
prepare_to_wait_exclusive(wq, &wait, TASK_INTERRUPTIBLE);
if (!signal_pending(current)) {
up(&rq->sem);
+ up_write(&ctx->state_sema);
pr_debug("%s: pid=%d prio=%d\n", __FUNCTION__,
current->pid, current->prio);
schedule();
+ down_write(&ctx->state_sema);
down(&rq->sem);
}
finish_wait(wq, &wait);
@@ -173,7 +176,9 @@
mm_needs_global_tlbie(spu->mm);
spu->ibox_callback = spufs_ibox_callback;
spu->wbox_callback = spufs_wbox_callback;
+ spu->stop_callback = spufs_stop_callback;
mb();
+ spu_unmap_mappings(ctx);
spu_restore(&ctx->csa, spu);
}
@@ -181,10 +186,12 @@
{
pr_debug("%s: unbind pid=%d SPU=%d\n", __FUNCTION__,
spu->pid, spu->number);
+ spu_unmap_mappings(ctx);
spu_save(&ctx->csa, spu);
ctx->state = SPU_STATE_SAVED;
spu->ibox_callback = NULL;
spu->wbox_callback = NULL;
+ spu->stop_callback = NULL;
spu->mm = NULL;
spu->pid = 0;
spu->prio = MAX_PRIO;
@@ -196,37 +203,35 @@
static struct spu *preempt_active(struct spu_runqueue *rq)
{
struct list_head *p;
- struct spu_context *ctx;
- struct spu *spu;
+ struct spu *worst, *spu;
- /* Future: implement real preemption. For now just
- * boot a lower priority ctx that is in "detached"
- * state, i.e. on a processor but not currently in
- * spu_run().
- */
+ worst = list_entry(rq->active_list.next, struct spu, sched_list);
list_for_each(p, &rq->active_list) {
spu = list_entry(p, struct spu, sched_list);
- if (current->prio < spu->prio) {
- ctx = spu->ctx;
- if (down_write_trylock(&ctx->state_sema)) {
- if (ctx->state != SPU_STATE_RUNNABLE) {
- up_write(&ctx->state_sema);
- continue;
- }
- pr_debug("%s: booting pid=%d from SPU %d\n",
- __FUNCTION__, spu->pid, spu->number);
- del_active(rq, spu);
- up(&rq->sem);
- unbind_context(spu, ctx);
- up_write(&ctx->state_sema);
- return spu;
- }
+ if (spu->prio > worst->prio) {
+ worst = spu;
+ }
+ }
+ if (current->prio < worst->prio) {
+ struct spu_context *ctx = worst->ctx;
+
+ spu = worst;
+ if (down_write_trylock(&ctx->state_sema)) {
+ pr_debug("%s: booting pid=%d from SPU %d\n",
+ __FUNCTION__, spu->pid, spu->number);
+ del_active(rq, spu);
+ up(&rq->sem);
+ wake_up_all(&ctx->stop_wq);
+ ctx->ops->runcntl_stop(ctx);
+ unbind_context(spu, ctx);
+ up_write(&ctx->state_sema);
+ return spu;
}
}
return NULL;
}
-static struct spu *get_idle_spu(u64 flags)
+static struct spu *get_idle_spu(struct spu_context *ctx, u64 flags)
{
struct spu_runqueue *rq;
struct spu *spu = NULL;
@@ -255,7 +260,7 @@
if ((spu = preempt_active(rq)) != NULL)
return spu;
}
- prio_wait(rq, flags);
+ prio_wait(rq, ctx, flags);
if (signal_pending(current)) {
prio_wakeup(rq);
spu = NULL;
@@ -322,7 +327,7 @@
if (ctx->spu)
return 0;
- spu = get_idle_spu(flags);
+ spu = get_idle_spu(ctx, flags);
if (!spu)
return (signal_pending(current)) ? -ERESTARTSYS : -EAGAIN;
bind_context(spu, ctx);
@@ -347,17 +352,19 @@
void spu_yield(struct spu_context *ctx)
{
struct spu *spu;
+ int need_yield = 0;
- if (!down_write_trylock(&ctx->state_sema))
- return;
+ down_write(&ctx->state_sema);
spu = ctx->spu;
- if ((ctx->state == SPU_STATE_RUNNABLE) &&
- (sched_find_first_bit(spu->rq->prio.bitmap) <= current->prio)) {
+ if (spu && (sched_find_first_bit(spu->rq->prio.bitmap) < MAX_PRIO)) {
pr_debug("%s: yielding SPU %d\n", __FUNCTION__, spu->number);
spu_deactivate(ctx);
ctx->state = SPU_STATE_SAVED;
+ need_yield = 1;
}
up_write(&ctx->state_sema);
+ if (unlikely(need_yield))
+ yield();
}
int __init spu_sched_init(void)