[linux-audio-user] Ingo's RT patch: please tell this newbie the best jack settings

Mark Knecht markknecht at gmail.com
Thu Nov 10 23:03:59 EST 2005

On 11/10/05, thewade <pdman at aproximation.org> wrote:
> Hello,
> I have given up on the mainstream Fedora 4 kernel and am trying to build
> 2.6.14-rt5. So far I can get it built and running, but without jack it
> seems.
> I am wondering what are the best settings for jack using Ingo's RT
> patch: how do I make the most of the patch?
> (I am trying to use CONFIG_PREEMPT_RT=y)
> I use qjackctl and my .jackrc is: /usr/local/bin/jackd -u -dalsa -dhw:1
> -r48000 -p128 -n2 -m -H -M
> hw:1 corresponds to the card number from /proc/asound/cards associated
> with my RME Hammerfall Multiface.
> I may have to change my .asoundrc as in the mainstream kernel cards 0
> and 1 are switched for some reason (if that is what is sotpping jackd).
> The only message I get is something to the effect of NTpolltime timed
> out, or something... My biggest question is not how to get jackd working
> - I will fix that. I am curious how to get PD running on my machine
> processing complex patches but with a latency of 5.33 msec (128 frame
> buffer size I think) or less. I would even settle fo 10msec (256) with
> no XRUNS.
> Thank you all for your help!
> -thewade

   A few comments:

1) The current kernel from Ingo would be 2.4.16-rt9. I think that rt5
didn;t last very long and had some problems. Please try -rt9.

2) Make sure you reinstall the realtime-lsm package after building that kernel.

3) Make sure you create a realtime group and modprobe realtime to
enable that group:

modprobe realtime gid=600 any=1

where gid=600 is for my realtime group in /etc/groups.

4) Making best use of the kernel requires that you understand the ISR
number for your sound card and reset it's priority higher. This helps
a lot in reducing or eliminating xruns.

5) Remove .jackrc completely and let your system set a new one.

6) Here are my HDSP 9652 settings:

jackd -R -p 64 -d alsa -r 44100 -p 64 -n2 -d hw:1,0

I get a few xruns at -p 64 -n2. I get none at -p 256 -n 2. I am still
looking for the root cause of the few xruns I get at 64/2.

7) Make sure you have the Jack FIFOS mounted on tmpfs.

As a comment, I don't personally like Jack in /usr local. You might
consider rebuilding Jack one of these days with:

./configure --prefix=/usr

Hope this all helps a bit,.


More information about the Linux-audio-user mailing list