On Mon, Aug 29, 2016 at 08:08:34AM +0100, Chris Wilson wrote:
> Currently we install a callback for performing poll on a dma-buf,
> irrespective of the timeout. This involves taking a spinlock, as well as
> unnecessary work, and greatly reduces scaling of poll(.timeout=0) across
> multiple threads.
>
> We can query whether the poll will block prior to installing the
> callback to make the busy-query fast.
>
> Single thread: 60% faster
> 8 threads on 4 (+4 HT) cores: 600% faster
>
> Still not quite the perfect scaling we get with a native busy ioctl, but
> poll(dmabuf) is faster due to the quicker lookup of the object and
> avoiding drm_ioctl().
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Need to strike the r-b here, since Christian König pointed out that
objects won't magically switch signalling on.
-Daniel
> ---
> drivers/dma-buf/dma-buf.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index cf04d249a6a4..c7a7bc579941 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -156,6 +156,18 @@ static unsigned int dma_buf_poll(struct file *file, poll_table *poll)
> if (!events)
> return 0;
>
> + if (poll_does_not_wait(poll)) {
> + if (events & POLLOUT &&
> + !reservation_object_test_signaled_rcu(resv, true))
> + events &= ~(POLLOUT | POLLIN);
> +
> + if (events & POLLIN &&
> + !reservation_object_test_signaled_rcu(resv, false))
> + events &= ~POLLIN;
> +
> + return events;
> + }
> +
> retry:
> seq = read_seqcount_begin(&resv->seq);
> rcu_read_lock();
> --
> 2.9.3
>
> _______________________________________________
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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