On Mon, 8 May 2006 21:54:53 +0200 Wolfgang Hoffmann <woho@xxxxxxx> wrote: > > I browsed over that page and didn't find any info on setting up the irq > > handler priorities which is _the_ essential feature of -rt. > > Apropos: on your page on -rt setup (excellent page, btw., many thanks! :-), > you suggest raising "softirq-timer/0" to prio 99, to make sleep() function > right (http://tapas.affenbande.org/?page_id=40 sleep() based/system timer). > > I did so, and got strange latencies (> 40 ms) exactly once every 10 minutes, > caused by some routing-related action (rt_secret_rebuild) being run by the > softirq-timer/0 thread. Don't you get bit by that, too? Kernel is 2.6.16-rt16 I haven't been bitten by that. Do you also get xruns with [i suppose so, just asking to make sure]? I haven't had as much time as before to play around and test things, so maybe it has crept into the kernel recently or maybe i just always had high-res timers enabled. > My solution is to configure with CONFIG_HIGH_RES_TIMERS=y. Then, sleep() wakes > up correctly even with softirq-timer/0 being low-priority (SCHED_FIFO 1 or > even SCHED_OTHER). > > In general I find adjusting priorities of the various softirq kernel threads a > bit of secret art. I can't find much documentation about "what kernel thread > runs which job" that would help making some proper decisions here. I found my > desktop "feels" most responsive when demoting all softirq thread to > SCHED_OTHER. I did so after seeing that with a non-rt kernel, bottom-half > handler don't run SCHED_FIFO/_RR at all. So -rt now gives me robust low > latencies for jackd, and still proper desktop feeling. > > Well, maybe this is getting off-topic for this list. But it seems to me > trimming priorities between kernel and userland threads is a bit like no > man's land. I agree. Maybe Lee Revell knows more [CC'ing him]. Lee, you know something about all these softirq threads? What exactly do they do? Regards, Flo -- Palimm Palimm! http://tapas.affenbande.org
