[Intel-gfx] [PATCH] UXA: Wait until a pageflip actually completes to report it.

[Eric Anholt]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> On Thu, May 08, 2014 at 08:54:52AM -0700, Eric Anholt wrote:
>> Chris Wilson <chris at chris-wilson.co.uk> writes:
>> 
>> > On Wed, May 07, 2014 at 10:44:23PM -0700, Jamey Sharp wrote:
>> >> On Wed, May 07, 2014 at 04:55:18PM +0100, Chris Wilson wrote:
>> >> > On Mon, May 05, 2014 at 11:05:07PM -0700, Jamey Sharp wrote:
>> >> > > UXA was reporting page-flip completion as soon as the flip was scheduled
>> >> > > with the kernel, instead of waiting for the kernel to indicate that the
>> >> > > flip had actually completed.
>> >> > > 
>> >> > > Moving the DRI2SwapComplete call to the right place fixes all of our
>> >> > > Piglit tests for OML_sync_control when run on xf86-video-intel/UXA,
>> >> > > aside from a bit of difficult-to-reproduce flakiness when using a
>> >> > > divisor > 1.
>> >> > 
>> >> > The violation is intentional, as it gives us triple buffering by
>> >> > default. It can be disabled.
>> >> 
>> >> As far as I can tell, this patch has no effect on triple-buffering. I
>> >> verified that by logging new_front->handle in intel_do_pageflip: It
>> >> rotates through three different BO's on successive flips.
>> >
>> > The patch blocks clients in GetBuffers until the swap completes,
>> > preventing them from rendering to the third buffer.
>> 
>> I don't see where the client gets blocked in a swapbuffers.  Can you
>> point that out?
>
> DRI2ThrottleClient() called by GetBuffers and SwapBuffers will call
> IgnoreClient() if swapsPending >= swap_limit and will only wake the
> client on calling DRI2SwapComplete(). The premature SwapComplete is to
> allow the clients next call to GetBuffers to succeed promptly returning
> the third buffer prior to the page flip completing.

Oh, so swap_limit is just set wrong?
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