[alsa-devel] MIDI playback not keeping steady time with recent kernels

Clemens Ladisch clemens at ladisch.de
Tue Feb 8 12:53:13 CET 2011

Arthur Marsh wrote:
>>> Arthur Marsh wrote, on 05/02/11 17:30:
>>>> MIDI playback either through xmms or aplaymidi won't keep regular time,
>>>> sounding weird going faster and slower under any kind of system load
>>>> except when nothing else is running.
> I've tried setting "options snd-timer timer_limit=x" where x is anywhere 
> from 5 down to 0, and seeing either:
> $ cat /proc/asound/seq/timer
> Timer for queue 0 : HR timer
>    Period time : 0.004000250
>    Skew : 65536 / 65536
> or "system timer" in place of "HR timer".
> In all cases, under sufficient load (which might be just running 
> aptitude -u), the tempo of the MIDI file play-back slows right down.

The ALSA interfaces of both the system timer and the HR timer do not
handle delayed interrupts correctly.  Please try the patch below, and if
it fixes the HR timer, tell me if you're OK with the published tag
Reported-and-tested-by: Arthur Marsh <arthur.marsh at internode.on.net>.


--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -45,12 +45,13 @@ static enum hrtimer_restart snd_hrtimer_
 	struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
 	struct snd_timer *t = stime->timer;
+	unsigned long oruns;
 	if (!atomic_read(&stime->running))
-	hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
-	snd_timer_interrupt(stime->timer, t->sticks);
+	oruns = hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
+	snd_timer_interrupt(stime->timer, t->sticks * oruns);
 	if (!atomic_read(&stime->running))

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