[PATCH] dma-buf: avoid scheduling on fence status query v2

[Christian König]

Am 26.04.2017 um 16:46 schrieb 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.
>
> v2: move early return after enable_signaling
>
> Signed-off-by: Andres Rodriguez <andresx7 at gmail.com>

Reviewed-by: Christian König <christian.koenig at amd.com>

> ---
>
>   If I'm understanding correctly, I don't think we need to register the
>   default wait callback. But if that isn't the case please let me know.
>
>   This patch has the same perf improvements as v1.
>
>   drivers/dma-buf/dma-fence.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 0918d3f..57da14c 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -402,6 +402,11 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
>   		}
>   	}
>   
> +	if (!timeout) {
> +		ret = 0;
> +		goto out;
> +	}
> +
>   	cb.base.func = dma_fence_default_wait_cb;
>   	cb.task = current;
>   	list_add(&cb.base.node, &fence->cb_list);