Messages in this thread | | | Date | Wed, 11 Aug 2004 15:44:14 +0200 | From | Florian Schmidt <> | Subject | Re: [patch] voluntary-preempt-2.6.8-rc3-O5 |
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On Wed, 11 Aug 2004 14:43:42 +0200 Ingo Molnar <mingo@elte.hu> wrote:
> > * Florian Schmidt <mista.tapas@gmx.net> wrote: > > > > i'm currently running a loop of mlockall-test 100MB on a 466 MHz > > > Celeron, and not a single blip on the radar with a 1000 usecs > > > threshold, after 1 hour of runtime ... > > > > I suppose you're not using jackd. As i have noticed that these > > critical sections only get reported when jackd is running. It seems > > jackd is producing a certain kind of load which exposes them.. > > so you can only trigger the latencies via mlockall-test if jackd is > also running?
Yes. I can happily mlockall 500 megs of ram when jackd is not running and i do not get any preempt-timing reports.. As soon as jackd is running even mlockall'ing only 20megs triggers a preempt-timing report and also a alsa xrun report. Hmm, let me try turning off xrun_debug traces while leaving preempt timing reports enabled...
Ok, when xrun_debug traces are disabled [but preempt timing is on]. mlocking 20 megs of memory triggers an xrun [now only reported by jackd in it's stdout, not in syslog] but not a preempt timing report. Lee, can you verify?
So it seems that the xrun_debug reports from the alsa interface jackd is using triggers the preempt timing reports. So these are really suspicious...
So i'm asking myself: How can jackd experience an xrun, when there's no preempt-timing report showing a kernel latency. Jackd is running SCHED_FIFO, so the mlockall_test program should not take away the cpu from jackd. Is mlockall() special in another way? Sorry, i know too little about the kernel internals to ask the right question. Maybe the alsa driver is reacting to the mlockall_test..
Another piece of info which might be valuable (i cannot judge this): I use jackd and mlockall not as root, but as normal user utilizing the realtime lsm which allows non root users to mlock, mlockall and change the scheduling class (via sched_setsched()?). I'll try runnign jackd and the mlockall_test as root to see if the results differ..
> Or do the latencies only trigger in jackd (and related > programs)?
Sorry, i don't understand that question..
> > if the later, then i'm wondering whether any of the audio code turns > off caching for specific pages or does DMA to user pages, or mmap()s > device(PCI) memory?
Flo
-- Palimm Palimm! http://affenbande.org/~tapas/
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