[Intel-gfx] [ANNOUNCE] xf86-video-intel 2.8.0

[Simon Farnsworth]

Barry Scott wrote:
> Ben Gamari wrote:
>> On Mon, Aug 03, 2009 at 04:12:22PM +0100, Barry Scott wrote:
>>   
>>> We think that the problem is that the GPU is basically serially
>>> reused. Only one window at a time gets GPU resources. This means that
>>> when the compositor creates the next frame and uses glxSwapBuffers to
>>> draw to screen the GPU goes idle waiting for the scan out line to be
>>> outside the visible area before doing the swap.  All others windows
>>> block in X waiting for the GPU resource to be free.
>>>     
>> I believe you could test this by disabling vblank synchronization in
>> driconf. Would definitely be a worthwhile thing to try.
>>   
> Rather then do this what we did was use XRender instead of OpenGL to 
> composite
> and we turned off XV tear free feature via the XV attribute. Then we use
> DRM VBLANK ioctl to time the frames for compositing.
> 
> This allows us to composite at 60 frames/second and be almost always
> tear free. (Almost because of the well know problem with intel graphics
> chips not having an accurate vblank interrupt).
> 
I should note here that we use the compositor to provide a "genlocked"
60 frames/second pulse to our other applications, so that they have a
source of frame times; we can cope with missing frames, but things go
funky if we have too many frames.

-- 
Simon Farnsworth