[Bug 42035] no way to turn off vsync

[Michel Dänzer]

On Don, 2011-10-27 at 23:47 +0200, Michal Suchanek wrote: 
> 2011/10/27 Michal Suchanek <hramrach at centrum.cz>:
> > 2011/10/27 Michel Dänzer <michel at daenzer.net>:
> >> On Mit, 2011-10-26 at 21:36 +0200, Michal Suchanek wrote:
> >>>
> >>> Ideally I would like no tearing and no vblank sync
> >>> but both tearing prevention in the radeon driver and sync to vblank
> >>> can lead to applications getting stuck in the  X server.
> >>
> >> Please provide details about a specific scenario where this happens with
> >> vblank_mode=0.
> >
> > Remove all configuration pertaining to vsync/vline wait.
> >
> > Run recent radeon driver on 3.0.0-10 Ubuntu kernel.
> >
> > Run glxgears. They won't render even a single frame unless the screen
> > is rotated.
> 
> Hmm, it does not depend on kernel version.
> 
> When two X servers are running the second one gets the stuck applications.

Ah! Assuming the first server is running GL clients, that's probably the
problem described in
http://lists.freedesktop.org/archives/dri-devel/2011-October/015677.html , starting with 'Also note that running drm_wait_ioctl as DRM_LOCKED is a severe problem that we have to address quickly'.


> >>> In the more recent snapshot the tearing prevention is not working
> >>> which is probably a bug in itself.
> >>
> >> Define 'not working'.
> >
> > fullscreen glxgears fps are not capped to the screen refresh rate.
> 
> With the current kernel and driver it seems to work more consistently.
> 
> Always synced on non-rotated screen and never synced on rotated, mapped or not.
> 
> At least fresh after booting. There seems to be some period about two
> weeks long in which the behaviour may vary :-S

Variance over time sounds like counter wraparound issues, but those
shouldn't affect vline waits...


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