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

[Andres Rodriguez]

CC a few extra lists I missed.

Regards,
Andres

On 2017-04-25 09:36 PM, Andres Rodriguez wrote:
> 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)) {
>