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Re: Vertical sync and KMS


On Sat, Nov 20, 2010 at 03:59:45PM +0100, Sven Arvidsson wrote:
> On Sat, 2010-11-20 at 13:34 +0100, Sylvain Beucler wrote:
> > Hi,
> > 
> > Since the switch to KMS (Kernel Mode Setting) in the current Debian, I
> > cannot get vertical sync to work with free 3D drivers.
> > 
> > (Vertical syncs caps the game framerate to the physical screen's
> > refresh rate, typically 60Hz, avoiding tearing and unnecessary display
> > updates, and permitting smooth scrolling.)
> > 
> > The only way to get vsync back is either use a proprietary driver or
> > switch back to UMS (in either case: when that's actually possible).  I
> > tried with 2 ATI Radeon cards and an Intel one, using a simple
> > scrolling demo with bare OpenGL, SDL 1.3 and Pyglet.
> > 
> > Do you get this issue in other distros, and do you know what's the
> > cause?
> It should work, for both radeon and intel, but I'm not sure if it's
> supported in Mesa 7.8. You might need 7.9 from experimental.

Thanks for the info.  Debian Squeeze's libgl1-mesa-dri is 7.7.1 btw.

I upgraded it to experimental on the Intel laptop and rebooted, but as
far as I can tell that doesn't help.

> Then either setting "vblank_mode=2" as an environment variable or or a
> drirc configuration like the one below should give you vertical sync:
>         <driconf>
>            <device screen="0" driver="dri2">
>               <application name="Default">
>                   <option name="vblank_mode" value="2" />
>               </application>
>             </device>
>         </driconf>

The system outputs something about overriding vblank_mode, but the FPS
stays at 400 in my test (with a 60Hz flat display).

With /etc/drirc or .drirc it additionaly mentions that option
vblank_mode is ignored.

It's possible that other packages need to be updated, including
kernel, dri kernel modules, and xorg.

Can I reformulate as: it should work, but only in bleeding edge?

Are there released distros where this works out of the box again?


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