3 Jan
2006
3 Jan
'06
10:55 p.m.
On Fri, 30 Dec 2005 17:04:24 +0100
Florian Schmidt <mista.tapas(a)gmx.net> wrote:
I also stumbled across some problems with sleep() and
especially waking
up when the sleep time has expired in the course of writing my
rt_watchdog program. Sometimes the high prio SCHED_FIFO thread wasn't
woken up as long as a lower SCHED_FIFO prio thread hugged the cpu even
when the sleep time of the high prio thread was long expired.. Ingo told
me back then that there's extra kernel threads for the timing subsystem
which need to be setup to high prios too for this to work correctly.
Haven't really investigated further into this.
I need to write another small test app that uses sleep based timing and
a high prio, too, to drive ughsynth. Will report what results i get.
Ok, as Ingo has told me before (and which i just remembered again
today):
To make sure threads actually do get woken up after their sleep() time
elapses one needs to make the softirq-timer/0 thread (only in -rt)
systems high priority, too (higher than jack).
I actually implemented a small sleep() based midi note generator
(similar to the rtc based one) and the results i get are a little worse
than with the rtc based timer, but not by thaaat much:
diff: 6047
diff: 5999
diff: 5999
adjusted midi event [frame offset >nframes] - handed to next period
diff: 5999
diff: 6048
diff: 5998
diff: 6000
diff: 6047
diff: 5999
diff: 5999
diff: 5999
diff: 6047
diff: 5999
diff: 6000
diff: 5999
diff: 6047
That's in the 1-2% jitter range which is still fine for me.
Rosegarden in 2.6.14 vanilla and with the adjusted softirq-timer/0
kernel thread works a lot better than w/o the adjustment (naturally)
when using the system timer as timing source.
So all -rt users beware, make your softirq-timer/0 thread high prio, too
:) Benefits seq24, too.
Regards,
Flo
P.S.: if you want to make your own experiments, here's the updated
tarball with the sleep() and rtc based test note generators (they only
produce note-on events though):
http://affenbande.org/~tapas/midi_timer-0.tgz
--
Palimm Palimm!
http://tapas.affenbande.org