Hi Chris and Gustavo,
On Mon, Aug 29, 2016 at 07:16:13PM +0100, Chris Wilson wrote:
> If we being polled with a timeout of zero, a nonblocking busy query,
> we don't need to install any fence callbacks as we will not be waiting.
> As we only install the callback once, the overhead comes from the atomic
> bit test that also causes serialisation between threads.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: Gustavo Padovan <gustavo at padovan.org>
> Cc: linux-media at vger.kernel.org
> Cc: dri-devel at lists.freedesktop.org
> Cc: linaro-mm-sig at lists.linaro.org
> ---
> drivers/dma-buf/sync_file.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index 486d29c1a830..abb5fdab75fd 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -306,7 +306,8 @@ static unsigned int sync_file_poll(struct file *file,
> poll_table *wait)
>
> poll_wait(file, &sync_file->wq, wait);
>
> - if (!test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
> + if (!poll_does_not_wait(wait) &&
> + !test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
> if (fence_add_callback(sync_file->fence, &sync_file->cb,
> fence_check_cb_func) < 0)
> wake_up_all(&sync_file->wq);
This commit is causing an error on one of the tests that Robert Foss
submitted for i-g-t. The one that does random merge of fences from
different timelines. A simple version of the test that still triggers
this is:
static void test_sync_simple_merge(void)
{
int fence1, fence2, fence_merge, timeline1, timeline2;
int ret;
timeline1 = sw_sync_timeline_create();
timeline2 = sw_sync_timeline_create();
fence1 = sw_sync_fence_create(timeline1, 1);
fence2 = sw_sync_fence_create(timeline2, 2);
fence_merge = sw_sync_merge(fence1, fence2);
sw_sync_timeline_inc(timeline1, 5);
sw_sync_timeline_inc(timeline2, 5);
ret = sw_sync_wait(fence_merge, 0);
igt_assert_f(ret > 0, "Failure triggering fence\n");
sw_sync_fence_destroy(fence_merge);
sw_sync_fence_destroy(fence1);
sw_sync_fence_destroy(fence2);
sw_sync_timeline_destroy(timeline1);
sw_sync_timeline_destroy(timeline2);
}
It looks like you cannot trust fence_is_signaled() without a
fence_add_callback(). I think the fence_array->num_pending won't get
updated. Although I couldn't figure out why it only happens if you merge
fences from different timelines.
Regards,
Rafael
