From 4ef110141b3e0758fe30d686417b5686b87eb25b Mon Sep 17 00:00:00 2001 From: Jeremy Kerr Date: Tue, 19 Feb 2008 10:05:35 +1100 Subject: [PATCH] [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 --- 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 fca22e18069a..6221968c2a3c 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 5915343e2599..3a5972117de7 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++;