[LAU] ubuntu 9.10 RT and Jack

Hartmut Noack zettberlin at linuxuse.de
Tue Nov 17 03:53:09 EST 2009

Hash: SHA1

Gary Morgan schrieb:
> i see..... well, then i guess i have to question my memlock or nice settings
> again, dont I?

I do not think that this will help much...

> My question now, would be: what are these settings actually doing? memlock
> seems to speak for itself, how much available mem is set for audio
> purposes...right?
>  but I dont see the difference between rtprio and nice,

nice does not help much if working with audio expect for some very
special needs (such as: running the computer as a synth for a
live-performance maybe..) It only affects the normal load-balancing as
used on the average Linux-system. I never experienced any usable
improvement in performance with running jack or ardour with nice -10 or

rtprio is the most important value. 99 is good (has always worked for
me) it allows group audio to wield the special preemption-magics that
are implemented with a rt-enabeled kernel.

> I only know that
> they handle interrupt priority in an indirect way. perhaps i've been setting
> them incorrectly; for nice and rtprio, the lowest number = highest priority?

rtprio is higher number = higher prio
nice is reversed

> Otherwise, I just don't see why each time i changed the settings, i would
> get no difference. It makes sense that my cpu would be constantly running at
> 60% if I were to set memlock to 50 or 60%, but the xrun count was always
> rediculous. and yes, tried restarts each time, for the jack server, and my
> computer itself.

I suspect your  audio-device as the weakest segment in your chain.
If you want to stick with it for now try to fiddle with the
jack-settings in qjackctl. Especially raising the number of
periods/buffer to 3 can do wonders with USB/FW or cheap onboard devices.
I also recommend to run jack with 48KHz or 96KHz - 44.1 does not perform
the same as good for me.
I run a cheapo-onboard chip with these settings:

/usr/bin/jackd -t1000 -u -dalsa -dhw:0 -r48000 -p512 -n3 -s -Xseq -zr

32ms latency is not really cool know but great performance does not come
at no-cost....

best regs


Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org


More information about the Linux-audio-user mailing list