[PD] Pd-extended + Ubuntu Gutsy generic kernel versus rt kernel

Daniel Wilcox danomatika at gmail.com
Mon Dec 24 18:54:12 CET 2007

To all those Pd Ubuntu-ers out there,

I have been using the realtime (lowlatency) kernel for a while, back since
Feisty, and compiled my own in Dapper.

I have noticed that, at least with Gusty, the generic kernel works better
then the rt kernel, giving me much *fewer*? xruns
and artifacting with Pd ... while using the rt kernel,  Pd seems to "sput"
xruns while using Jack.  It's important to note that I
did enable the realtime privledges by writing to the security config as
noted on the Ubuntu studio page:
     sudo su -c 'echo @audio - rtprio 99 >> /etc/security/limits.conf'
     sudo su -c 'echo @audio - memlock 250000 >> /etc/security/limits.conf'
     sudo su -c 'echo @audio - nice -10 >> /etc/security/limits.conf'

Could it be that the preemption enabled in the rt kernel is a bit *too*
aggressive?  Realtime audio in PD with Jack seems to run much
better with the generic kernel!  Even at a 8ms latency ... in fact I'm
testing the same on my slow performance computer (PIII 500MHz) with a fresh
install of a Minimal command line Gutsy and it works *soooo* much better
then the realtime kernel.  (Plus suspend and
hibernation work, while they don't using the realtime kernel.)

Dan Wilcox
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