[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 <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
diff --git a/arch/powerpc/platforms/cell/spufs/context.c b/arch/powerpc/platforms/cell/spufs/context.c
index 056a8ad..d581f4e 100644
--- a/arch/powerpc/platforms/cell/spufs/context.c
+++ b/arch/powerpc/platforms/cell/spufs/context.c
@@ -53,6 +53,7 @@
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 eb06a03..814f65e 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -282,6 +282,74 @@
}
/**
+ * 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
* @flags: flags (currently ignored)
@@ -300,6 +368,12 @@
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 421f591..85b182d 100644
--- a/arch/powerpc/platforms/cell/spufs/spufs.h
+++ b/arch/powerpc/platforms/cell/spufs/spufs.h
@@ -83,6 +83,7 @@
/* scheduler fields */
struct list_head rq;
unsigned long sched_flags;
+ unsigned long rt_priority;
int prio;
};