[Bug 42035] no way to turn off vsync

[Michel Dänzer]

On Mit, 2011-10-26 at 12:05 +0200, Michal Suchanek wrote: 
> 2011/10/26 Michel Dänzer <michel at daenzer.net>:
> > On Die, 2011-10-25 at 20:41 +0200, Michal Suchanek wrote:
> >> 2011/10/25 Michel Dänzer <michel at daenzer.net>:
> >> > On Mon, 2011-10-24 at 23:23 +0200, Michal Suchanek wrote:
> >> >> With this patch it should be at least possible to turn off all this
> >> >> when it does not work.
> >> >
> >> > Exactly. So, have you had a chance to try it?
> >>
> >> I installed the packages I built yesterday. The patch has no visible effect.
> >
> > Well, I do see an effect in the log file:
> >
> > [2558366.995] (==) RADEON(0): SwapBuffers wait for vblank: disabled
> >
> >
> >> > Does it address your bug report?
> >>
> >> I am not quite sure.
> >
> > The above means the thing the bug report complains about being
> > impossible to disable is disabled.
> 
> Still it is disabled without the patch too, which it supposedly should not.

I don't see how that can be the case with a driver built from unpatched
upstream, without (the equivalent of) Option "SwapbuffersWait" "off".


> >> With the current Radeon driver ( xserver-xorg-video-radeon
> >> 1:6.14.99+git20111024.856583db-0ubuntu0sarvatt~natty patched or not)
> >> and X server 1.10.4 I could reliably reproduce a lockup on start of
> >> glxgears on the primary screen with vsync enabled in drirc.
> >
> > That would be a different bug then. You could try finding out where
> > things get stuck by attaching gdb to glxgears and/or the X server.
> 
> The trace shows it stuck in DRI2GetBuffersWithFormat.
> 
> Since the X server continues running I don't think I can figure out
> where *that* is stuck.

It's probably waiting for a DRM VBLANK event. The question then becomes
why that never arrives.


> Maybe a newer X server would behave differently, 1.10 is not exactly new.

It's worth a try, but I wouldn't expect any miracles.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer