rt kernel

[Ralf Mardorf]

On Wed, 2011-04-06 at 11:03 +0100, Bernard Hurley wrote:
> Hi
> 
> On Wed, Apr 06, 2011 at 11:47:02AM +0200, Ralf Mardorf wrote:
> > Hi all :)
> > 
> > 
> > Note that today we should prefer the tickless timer. I'm enabling it on
> > Maverick by my session start scripts:
> > 
> > lsmod | grep snd_hrtimer
> >  case $? in
> >     1)
> > 	echo "Enabling HR TIMER for ALSA MIDI playback queue timer resolution
> > 1000000000 Hz"
> > 	sudo chgrp audio /dev/hpet
> >         sudo chmod g+rw /dev/hpet
> > 	sudo modprobe snd-hrtimer
> > 	;;
> >     *)
> >         echo "HR TIMER for ALSA MIDI playback queue timer resolution
> > 1000000000 Hz is enabled"
> >         ;;
> >  esac
> > 
> > The 1000 Hz timer still isn't obsolet, because HPET/HR timer sometimes
> > does cause issues on some machines, resp. when running some apps, e.g.
> > Rosegarden will freeze the computer, but e.g. Qtractor is working.
> > Anyway, using the tickless timer when ever possible, will cause
> > something that is nearer to 'hard real time'.
> > HPET is enabled for Maverick's kernel 2.6.35-28-generic too.
> 
> Does this mean I can't use Rosegarden if I do this? Or is there some way of using both timers?

Yes, rep. you should test this on your machine. Btw. I need to start
'qtractor filename', if I run qtractor and then load the song, it
doesn't work, because the timer already is occupied.

I only need HR timer to get less jitter when recording external MIDI
synth, but even then jitter is to extrem for music ... regarding to the
ALSA MIDI latency test my machine get best results for jitter, but I'm
sure his test is nonsense. BTW., I guess JACK audio does cause a lot of
jitter too (MIDI events with negativ delay ;).

When recording internal (virtual) synth, there usually is no jitter,
even when just using the 1000 Hz timer.

> 
> > 
> > FWIW compiling 2.6.33.7.2-rt30 for Maverick is easy to do, I posted a
> > scrip on that list.
> > 
> 
> Thanks I'll have a look at this.
> 
>   /Bernard
>