OpenGL video performance

Greg G. dargllun at
Wed May 2 11:09:37 PDT 2012

On 01.05.2012 09:49, Michel Dänzer wrote:
> On Fre, 2012-04-27 at 17:21 +0200, Greg G. wrote:
>> What I keep thinking about: could there any problem arise from the way
>> the driver allocates VRAM? Can there be resource conflicts, effectively
>> limiting the GL troughput only be cause some memory is already used, for
>> example by EXA?
> In theory yes, but only if the working sets of all running apps exceed
> the amount of VRAM, which is unlikely for the scenarios you've
> described.

As a follow up to this, I just browsed through an older thread on the 
mythtv-users list discussing the same issue. Quoting from the following 
post of one of the mythtv devs:
------------ quote
You have to bear in mind that the single biggest bottleneck for OpenGL
deinterlacing performance is texture sampling.

When no deinterlacing is taking place, there is one texture sample per
pixel (we do some packing of the video frame data in software before
sending it to the gpu to avoid sampling for the luma and both

When you are using the OpenGL kernel deinterlacer, there are 8 texture
samples for each pixel in the frame. Depending on your gpu, gpu memory
type and speed, video resolution etc, this may simply be too slow. You
may not be using the cpu to perform deinterlacing, but the gpu still
has a finite time to complete the process before the frame needs to be
------------ /quote

Perhaps mythtv _is_ overly using resources? Could I try any xorg.conf 
setting to shift resource management towards favouring opengl?


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