[PATCH] dma-buf: avoid scheduling on fence status query

[Andres Rodriguez]

When a timeout of zero is specified, the caller is only interested in
the fence status.

In the current implementation, dma_fence_default_wait will always call
schedule_timeout() at least once for an unsignaled fence. This adds a
significant overhead to a fence status query.

Avoid this overhead by returning early if a zero timeout is specified.

Signed-off-by: Andres Rodriguez <andresx7 at gmail.com>
---

This heavily affects the performance of the Source2 engine running on
radv.

This patch improves dota2(radv) perf on a i7-6700k+RX480 system from
72fps->81fps.

 drivers/dma-buf/dma-fence.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 0918d3f..348e9e2 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -380,6 +380,9 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
 	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 		return ret;
 
+	if (!timeout)
+		return 0;
+
 	spin_lock_irqsave(fence->lock, flags);
 
 	if (intr && signal_pending(current)) {
-- 
2.9.3