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 --- 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();