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

[Rich E]

On Wed, May 21, 2008 at 3:20 PM, Ken Restivo <ken at restivo.org> wrote:

>
> 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.
>

Ken, this made me laugh for quite a while.  Thank you.


>
> 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.
>

I had it on my last setup, but for got to do it this time.  Thanks for
reminding me :)  Also, as my other post mentions, I sometimes got clicks
with pd even with the script.  I actually had to change the irq priority of
pd to get rid of them, which is bad since it changes all the threads pd has
instead of only the scheduler.   I would get "I/O stuck... closing audio"
all the time.


>
> -ken
>
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