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 <ch...@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.sem...@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: dri-de...@lists.freedesktop.org
Cc: linaro-mm-...@lists.linaro.org
---
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
--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
