[PATCH] dma-buf: Do a fast lockless check for poll with timeout=0

[Chris Wilson]

On Sun, Aug 28, 2016 at 05:37:47PM +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

Hmm, this only really applies to the idle case.
reservation_object_test_signaled_rcu() is still a major bottleneck when
busy, due to the dance inside reservation_object_test_signaled_single()
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre