Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=4ef110141b3e0758fe30d686417b5686b87eb25b
Commit: 4ef110141b3e0758fe30d686417b5686b87eb25b
Parent: 101142c37be8e5af9b847860219217e6b958c739
Author: Jeremy Kerr <[EMAIL PROTECTED]>
AuthorDate: Tue Feb 19 10:05:35 2008 +1100
Committer: Jeremy Kerr <[EMAIL PROTECTED]>
CommitDate: Tue Feb 19 10:12:02 2008 +1100
[POWERPC] spufs: fix scheduler starvation by idle contexts
2.6.25 has a regression where we can starve the scheduler by creating
(N_SPES+1) contexts, then running them one at a time.
The final context will never be run, as the other contexts are loaded on
the SPEs, none of which are repoted as free (ie, spu->alloc_state !=
SPU_FREE), so spu_get_idle() doesn't give us a spu to run on. Because
all of the contexts are stopped, none are descheduled by the scheduler
tick, as spusched_tick returns if spu_stopped(ctx).
This change replaces the spu_stopped() check with checking for SCHED_IDLE
in ctx->policy. We set a context's policy to SCHED_IDLE when we're not
in spu_run(). We also favour SCHED_IDLE contexts when looking for contexts
to unbind, but leave their timeslice intact for later resumption.
This patch fixes the following test in the spufs-testsuite:
tests/20-scheduler/02-yield-starvation
Signed-off-by: Jeremy Kerr <[EMAIL PROTECTED]>
---
arch/powerpc/platforms/cell/spufs/run.c | 1 +
arch/powerpc/platforms/cell/spufs/sched.c | 8 +++-----
2 files changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/platforms/cell/spufs/run.c
b/arch/powerpc/platforms/cell/spufs/run.c
index fca22e1..6221968 100644
--- a/arch/powerpc/platforms/cell/spufs/run.c
+++ b/arch/powerpc/platforms/cell/spufs/run.c
@@ -234,6 +234,7 @@ static int spu_run_fini(struct spu_context *ctx, u32 *npc,
*npc = ctx->ops->npc_read(ctx);
spuctx_switch_state(ctx, SPU_UTIL_IDLE_LOADED);
+ ctx->policy = SCHED_IDLE;
spu_release(ctx);
if (signal_pending(current))
diff --git a/arch/powerpc/platforms/cell/spufs/sched.c
b/arch/powerpc/platforms/cell/spufs/sched.c
index 5915343..3a59721 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -856,21 +856,18 @@ static noinline void spusched_tick(struct spu_context
*ctx)
{
struct spu_context *new = NULL;
struct spu *spu = NULL;
- u32 status;
if (spu_acquire(ctx))
BUG(); /* a kernel thread never has signals pending */
if (ctx->state != SPU_STATE_RUNNABLE)
goto out;
- if (spu_stopped(ctx, &status))
- goto out;
if (ctx->flags & SPU_CREATE_NOSCHED)
goto out;
if (ctx->policy == SCHED_FIFO)
goto out;
- if (--ctx->time_slice)
+ if (--ctx->time_slice && ctx->policy != SCHED_IDLE)
goto out;
spu = ctx->spu;
@@ -880,7 +877,8 @@ static noinline void spusched_tick(struct spu_context *ctx)
new = grab_runnable_context(ctx->prio + 1, spu->node);
if (new) {
spu_unschedule(spu, ctx);
- spu_add_to_rq(ctx);
+ if (ctx->policy != SCHED_IDLE)
+ spu_add_to_rq(ctx);
} else {
spu_context_nospu_trace(spusched_tick__newslice, ctx);
ctx->time_slice++;
-
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