On Fri, Sep 23, 2016 at 07:59:44PM +0200, Christian König wrote:

Am 23.09.2016 um 17:20 schrieb Chris Wilson:

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On Fri, Sep 23, 2016 at 03:50:44PM +0200, Daniel Vetter wrote:

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On Mon, Aug 29, 2016 at 08:08:34AM +0100, Chris Wilson wrote:

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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.

Oh, it also means that

commit fb8b7d2b9d80e1e71f379e57355936bd2b024be9 Author: Jammy Zhou Jammy.Zhou@amd.com Date: Wed Jan 21 18:35:47 2015 +0800

 reservation: wait only with non-zero timeout specified (v3)
 When the timeout value passed to reservation_object_wait_timeout_rcu
 is zero, no wait should be done if the fences are not signaled.
 Return '1' for idle and '0' for busy if the specified timeout is '0'
 to keep consistent with the case of non-zero timeout.
 v2: call fence_put if not signaled in the case of timeout==0
 v3: switch to reservation_object_test_signaled_rcu
 Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
 Reviewed-by: Christian König <christian.koenig@amd.com>
 Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
 Reviewed-By: Maarten Lankhorst <maarten.lankhorst@canonical.com>
 Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

is wrong. And reservation_object_test_signaled_rcu() is unreliable.

Ups indeed, that patch is wrong as well.

I suggest that we just enable the signaling in this case as well.

Will you/Zhou take care of this corner case? Just so I can't forget about it ;-)

Thanks, Daniel