powerpc/spufs: Explain conditional decrement of aff_sched_count

This patch adds a comment to clarify why atomic_dec_if_positive is being used
to decrement gang's aff_sched_count on SPU context unbind.

Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 6253df5..2ad914c 100644 (file)
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -444,6 +444,11 @@ static void spu_unbind_context(struct spu *spu, struct spu_context *ctx)
                atomic_dec(&cbe_spu_info[spu->node].reserved_spus);
 
        if (ctx->gang)
+               /*
+                * If ctx->gang->aff_sched_count is positive, SPU affinity is
+                * being considered in this gang. Using atomic_dec_if_positive
+                * allow us to skip an explicit check for affinity in this gang
+                */
                atomic_dec_if_positive(&ctx->gang->aff_sched_count);
 
        spu_switch_notify(spu, NULL);