[linux-audio-dev] 2.4.20-rc1 + lowlat + preempt + alsa + jack = dead computer

Fernando Pablo Lopez-Lezcano nando at ccrma.Stanford.EDU
Fri Nov 1 19:05:01 UTC 2002

[sorry for the wide distribution]
Is anyone out there trying out this combination?:

  kernel 2.4.20-rc1
  capabilities patch
  low latency patch
  preemptible kernel patch
  almost current alsa cvs [20021028.170432 usa pacific time]

If I start jackd and then use the freqtweak jack client I get a completely
dead machine in a very short time (from a few seconds to 10 or 20

Same alsa driver, but running on 2.4.19 (up to 20-pre4) seems to be fine
and I can play around with freqtweak for as long as I want :-)

No clues are left behind... something in the kernel is deadlocking, I
guess. I tried removing first the preemptible kernel patch with the same
result.  Just a moment ago I tried again after removing the low latency
patch and I still get the same result... that pretty much leaves alsa and
the kernel. Got the same result on a laptop intel810 and an ice1712 card.

Interestingly enough just the jack server running is not enough to kill
the machine. Adding a jack client (just tried alsaplayer, same problem as
freqtweak) kills the machine really fast.

Maybe there is a problem with the scheduler when there are several
SCHED_FIFO tasks competing for the processor?

-- Fernando

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