[Bug 42035] no way to turn off vsync

[Michal Suchanek]

2011/10/26 Michel Dänzer <michel at daenzer.net>:
> 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.
>

Indeed, the latest (unpatched) Ubuntu packages (some 1.11 branch X
server) give the same results.

That is SwapbuffersWait defaults to off or is broken and vblank wait
in dri defaults to on.

This makes glxgears stuck before displaying the first frame on
non-rotated screens.

When I turn off vblank wait glxgears run.

Thanks

Michal