[Bug 42035] no way to turn off vsync

[Michel Dänzer]

On Mit, 2011-10-26 at 21:36 +0200, Michal Suchanek wrote:
> 
> Ideally I would like no tearing and no vblank sync

Well, the only way to avoid tearing without sync to vblank is the method
controlled by Option "SwapbuffersWait"...


> 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. 


> However, the tearing prevention does in practice vblank sync, at least
> for fullscreen windows.

For fullscreen windows, scanout is only outside of the window during
vertical blank. 

> So the practical difference is minimal since most GL rendering would
> occur in large windows. 

The main difference is that sync to vblank waits for CPU interrupts,
whereas the vline waits happen in the GPU command processor. 


> In the more recent snapshot the tearing prevention is not working
> which is probably a bug in itself.

Define 'not working'.


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