[Cbe-oss-dev] PATCH [4/7] decouple spu scheduler from spufs_spu_run [asynchronous scheduling]

[Christoph Hellwig]

On Wed, Oct 31, 2007 at 09:07:18PM -0300, Luke Browning wrote:
> 
> This patch changes spufs_spu_run so that the context is queued 
> directly to the scheduler and the controlling thread advances
> directly to spufs_wait() for spe errors and exceptions.
> 
> Isolated (No-sched) contexts are treated the same as before.

This deadlocks instantly once we overcommit spu ressources because
spusched_tick runs with the list_mutex held and spu_unschedule/
spu_schedule try to take it again.  

spu_unschedule could easily be fixed by adding a __spu_unschedule that
expects the list_lock to be held, but for the spu_schedule case the
code is more complex and we need to duplicate it in spusched_tick,
so I bit the bullet and put an opencoded version of unbind+bind
into spusched_tick where we can avoid decrementing nr_active just
to increment it again and fuzz with the alloc_state.

With this fix most of Jeremy's testsuite passed except for some dma
alignment tests.

Signed-off-by: Christoph Hellwig <hch at lst.de>


Index: linux-2.6/arch/powerpc/platforms/cell/spufs/sched.c
===================================================================
--- linux-2.6.orig/arch/powerpc/platforms/cell/spufs/sched.c	2007-11-23 12:37:05.000000000 +0100
+++ linux-2.6/arch/powerpc/platforms/cell/spufs/sched.c	2007-11-23 13:06:12.000000000 +0100
@@ -864,14 +869,21 @@
 
 		new = grab_runnable_context(ctx->prio + 1, spu->node);
 		if (new) {
-			spu_unschedule(spu, ctx);
+			spu_unbind_context(spu, ctx);
+			ctx->stats.invol_ctx_switch++;
+			spu->stats.invol_ctx_switch++;
 			spu_add_to_rq(ctx);
+			mutex_unlock(&ctx->state_mutex);
+
+			mutex_lock(&new->state_mutex);
+			spu_set_timeslice(new);
+			spu_bind_context(spu, new);
+			wake_up_all(&new->run_wq);
+			mutex_unlock(&new->state_mutex);
 		} else {
 			spu_set_timeslice(ctx);
+			mutex_unlock(&ctx->state_mutex);
 		}
-		mutex_unlock(&ctx->state_mutex);
-		if (new)
-			spu_schedule(spu, new);
 	} else {
 		ctx->time_slice++;
 	}