On Thu, Feb 12, 2004 at 08:56:52AM -0800, Ian Romanick wrote:
> Christian Henz wrote:
> 
> >On Linux-2.6.x (test-1 up to the recent 2.6.2), I have a nasty problem when
> >running the jack audio platform (jackit.sf.net) in realtime mode (uses 
> >mlockall, SCHED_FIFO) and starting Qt-based jack clients like qjackctl, 
> >hydrogen, simsam (all at .sf.net). The clients freeze and afterwards, ps, 
> >top, killall etc. freeze on execution. kill still works if you have 
> >memorized a pid before, but the clients cannot be killed. Also the system 
> >will hang on shutdown
> >when some init scripts try to kill processes.
> >
> >Non-Qt clients work fine, also all clients work with DRI disabled in 
> >XF86Config-4, or when running jackd in non-realtime mode. Additionally 
> >everything works fine in Linux-2.4.x with DRI enabled.
> >
> >I've installed DRI/DRM from CVS yesterday, but the problem still exists.
> >
> >I'm using an original Radeon (radeon driver) with 32MB SDR-RAM. DRI itself
> >works fine. My MoBo has the Via686a chipset (via-agp in Linux-2.6.2)
> >
> >I'm attaching an strace of one of the offending apps (simsam) and my X log.
> >
> >I hope someone can help me on this one.
> 
> So, I guess I don't understand why this is a graphics driver issue.  Is 
> it the graphics driver that's causing the lock or the sound driver?
> 

As far as I can tell it is the graphics driver. The jack client portion of 
the application actually seems to keeps running (in a different thread), and
so does jackd, and other clients are actually producing sound while this all 
happens. Qt makes use of glx, and therefore - if enabled - of DRI (at least 
that's what I understand). When looking at the strace output it seems that
the freeze occurs while doing something DRI-related. 

My guess is that it happens because the jack client part calls mlockall if 
jackd runs in realtime mode. This seems to be problematic in combination with 
some DRI drivers, it came up recently on the linux-audio-developers mailing
list (http://eca.cx/lad/2004/02/0142.html, http://eca.cx/lad/2004/02/0145.html)

But then again it works for me on linux 2.4.x...


cheers,
Christian Henz


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