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

Florian Schmidt mista.tapas at gmx.net
Fri Nov 11 06:13:54 EST 2005

On Thu, 10 Nov 2005 20:03:59 -0800
Mark Knecht <markknecht at gmail.com> wrote:

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

jackd -R -P 70 ...

to set the priority of jackd higher than all soundcard irq handlers
besides the soundcard irq.

Basically the priority setup should look something like this:

keyboard irq handler   - 99
rtc irq handler        - 99
soundcard irq handler  - 98

jackd prio             - 70 (creates watchdog at prio 80 and client
process() threads at prio 69)

all other irq handlers - around 50 (default)

Basically there's also some problems with the timer irq's on -rt kernels
(which my rt watchdog suffers from). Usually you would want to set
softirq-timer and softirq-ktime to high prios, too (so high prio
sleeping threads preempt low prio running threads when getting woken up.
Actually this should make sure that the timer interrupt which wakes up
the high prio thread after its sleep actually gets to run), but this
doesn't quite work with the kernels i tested (this is the reason why my
rt_watchdog doesn't work right).

I'll try with newer kernels and ask ingo about it if the problem
persists. Anyways, this should really only be a problem with midi
sequencers that are sleep based. When using an irq source for timing
this problem should go away.


Palimm Palimm!

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