[PD] wierd feedback popping with pd/freebob/jack/rt

[Ken Restivo]

On Wed, May 21, 2008 at 02:23:20PM -0700, Rich E wrote:
> >
> > IIRC, Ubuntu "RT" kernel is not actually Real Time (i.e. with Ingo
> > patches), just a "desktop RT" which is not very useful for audio and
> > certainly not enough for JACK apps of any heft.
> >
> 
> Where are you getting this info from?  This is not what I have read, but
> maybe I am missing something somewhere.  I thought that the Ubuntu kernel
> packagers recently switched to using full realtime preemption... I find this

My info is from having installed Ubuntu and used it... but that was a few years ago. Glad they're using Ingo's patches now.


> in the package description of linux-image-2.6.22-14-rt :
> Ingo Molnar's full real time preemption patch (2.6.22.1-rt9)
> 
> Here is the output of uname -a:
> Linux pal 2.6.22-14-rt #1 SMP PREEMPT RT Tue Feb 12 09:57:10 UTC 2008 i686
> GNU/Linux
> 
> .. and here are the kernel settings from  cat /boot/config-2.6.22-14-rt |
> grep PREEMPT
> # CONFIG_PREEMPT_NONE is not set
> # CONFIG_PREEMPT_VOLUNTARY is not set
> # CONFIG_PREEMPT_DESKTOP is not set
> CONFIG_PREEMPT_RT=y
> CONFIG_PREEMPT=y
> CONFIG_PREEMPT_SOFTIRQS=y
> CONFIG_PREEMPT_HARDIRQS=y
> CONFIG_PREEMPT_BKL=y
> CONFIG_PREEMPT_RCU=y
> # CONFIG_DEBUG_PREEMPT is not set
> # CONFIG_CRITICAL_PREEMPT_TIMING is not set
>
> Looks realtime to me.. also the latency is really low (5-10ms
> conservatively), much lower than I have experienced on other OS's, with or
> without realtime.  But, if you know something I don't... I have open ears.

Nope, you got real-time there, for sure. I was wrong then.

> Ubuntu runs so nicely on a laptop though... would hate to switch after
> finding such an easy-to-operate linux distribution because pd and only pd
> doesn't like jack in realtime.
> 

Dunno. You're playing Xrun whack-a-mole. Done that; it's not fun.

Here's what I did to RT-ify my system (on Debian, but Ubuntu is based on it):
http://www.restivo.org/blog/archives/preparing-a-debian-etch-system-for-audio-use

Also, I expect you know to use chrt to give the IRQ of your audio interface top priority, higher than JACK and any other process. That's a crucial step. If I omit that, then I get clicks and pops too, which is why I wrote a script to do it automatically. You could also install and configure the "rtirq" package, which works great too.

-ken