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@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
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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