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

[Chris Wilson]

On Thu, May 08, 2014 at 01:55:30PM -0700, Eric Anholt wrote:
> 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?

Yes.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre