From 52f04fcf66a5d5d90790d6cfde52e391ecf2b882 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Tue, 13 Feb 2007 21:54:27 +0100 Subject: [PATCH] [POWERPC] spu sched: forced preemption at execution If we start a spu context with realtime priority we want it to run immediately and not wait until some other lower priority thread has finished. Try to find a suitable victim and use it's spu in this case. Signed-off-by: Christoph Hellwig Signed-off-by: Arnd Bergmann --- arch/powerpc/platforms/cell/spufs/context.c | 1 + arch/powerpc/platforms/cell/spufs/sched.c | 74 +++++++++++++++++++++ arch/powerpc/platforms/cell/spufs/spufs.h | 1 + 3 files changed, 76 insertions(+) diff --git a/arch/powerpc/platforms/cell/spufs/context.c b/arch/powerpc/platforms/cell/spufs/context.c index 056a8ad023..d581f4ec99 100644 --- a/arch/powerpc/platforms/cell/spufs/context.c +++ b/arch/powerpc/platforms/cell/spufs/context.c @@ -53,6 +53,7 @@ struct spu_context *alloc_spu_context(struct spu_gang *gang) ctx->owner = get_task_mm(current); if (gang) spu_gang_add_ctx(gang, ctx); + ctx->rt_priority = current->rt_priority; ctx->prio = current->prio; goto out; out_free: diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c index eb06a030ca..814f65e025 100644 --- a/arch/powerpc/platforms/cell/spufs/sched.c +++ b/arch/powerpc/platforms/cell/spufs/sched.c @@ -281,6 +281,74 @@ static struct spu *spu_get_idle(struct spu_context *ctx) 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(node)) + continue; + + mutex_lock(&spu_prio->active_mutex[node]); + list_for_each_entry(spu, &spu_prio->active_list[node], list) { + struct spu_context *tmp = spu->ctx; + + if (tmp->rt_priority < ctx->rt_priority && + (!victim || tmp->rt_priority < victim->rt_priority)) + victim = spu->ctx; + } + mutex_unlock(&spu_prio->active_mutex[node]); + + 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; + } + spu_unbind_context(spu, victim); + mutex_unlock(&victim->state_mutex); + return spu; + } + } + + return NULL; +} + /** * spu_activate - find a free spu for a context and execute it * @ctx: spu context to schedule @@ -300,6 +368,12 @@ int spu_activate(struct spu_context *ctx, unsigned long flags) struct spu *spu; 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 && ctx->rt_priority) + spu = find_victim(ctx); if (spu) { spu_bind_context(spu, ctx); return 0; diff --git a/arch/powerpc/platforms/cell/spufs/spufs.h b/arch/powerpc/platforms/cell/spufs/spufs.h index 421f59167c..85b182d164 100644 --- a/arch/powerpc/platforms/cell/spufs/spufs.h +++ b/arch/powerpc/platforms/cell/spufs/spufs.h @@ -83,6 +83,7 @@ struct spu_context { /* scheduler fields */ struct list_head rq; unsigned long sched_flags; + unsigned long rt_priority; int prio; }; -- 2.39.5