A simple accelerated GL compositor

Felix Bellaby felix at bellaby.plus.com
Sat Jul 8 04:37:53 PDT 2006

Mike Russo wrote:
> Felix Bellaby wrote:
> > What use of the Composite extension were you making to get a MTBF of 2-3
> > days? The problems that I been working on have a MTBF of a few minutes,
> > though the failures might still be related.
> >   
> Nothing more complicated than running
> xcompmgr -fF -cC -r7 -o.65 -l-10 -t-8 -D3 &
> in my .xinitrc and setting the transparency on individuals windows using 
> transset-df.  Random crashes (SIGSEGVS with the occasional floating 
> point error in the  nvidia signal handler function) would crash X every 
> few days with no noticeable pattern, although others have complained on 
> the nvnews.net forums of crashes when certain KDE apps (kopete) are 
> running.   If the stability problems continue, perhaps the strategy of 
> enabling Composite through GLX will work better. XGL was more stable in 
> that it did not have random crashes, but leaked memory so bad that after 
> 3 days it would get killed anyway. :)

Which were the latest nvidia drivers that you used intensively with
xcompmgr ? 

The main points of contact between xcompmgr and my code now reside in
the Xcomposite library calls, which are basically unchanged. I would
expect to see similar crashes to the ones you describe from my code if
the problem lay in the nvidia built-in COMPOSITE extension. I will see
if I can reproduce them using a long run test.

It is possible that xcompmgr was hitting bugs in other parts of the
nvidia drivers. It makes heavy use of the nvidia built-in XFIXES and
DAMAGE extensions. My more limited demands on the DAMAGE extension
should avoid significant reliance the XFIXES extension code. I also
avoid all use of the RENDER extension, which might have bugs where it
interacts with XFIXES. 

If the long term crashes are coming from COMPOSITE extension itself,
then we still have a chance of them being fixed, because nvidia will
need to revisit one of the tricky parts of that code (handing off Pixmap
references) to address the GLXPixmap bug that I discovered.

Do not hold your breath, but things might be looking up. The GLX and GL
code should be well tested by nvidia, so stability should increase when
we rely less on other extensions. 


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