Re: MIDI playback not keeping steady time with recent kernels

Re: MIDI playback not keeping steady time with recent kernels

[Clemens Ladisch]

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@internode.on.net>.


Regards,
Clemens

--- 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))
 		return HRTIMER_NORESTART;
 
-	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))
 		return HRTIMER_NORESTART;

Re: MIDI playback not keeping steady time with recent kernels

[Arthur Marsh]

Clemens Ladisch wrote, on 08/02/11 22:23:
> 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@internode.on.net>.
>
>
> Regards,
> Clemens
>
> --- 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))
>   		return HRTIMER_NORESTART;
>
> -	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))
>   		return HRTIMER_NORESTART;
>

OK, I applied this patch.

When the MIDI file was playing:

$ cat /proc/asound/seq/timer
Timer for queue 0 : HR timer
   Period time : 0.004000250
   Skew : 65536 / 65536

I still experienced some slow-down and speed-up under heavy load.

Thanks for the patch. I'm happy to do any further testing you can suggest.

Regards,

Arthur.

Re: MIDI playback not keeping steady time with recent kernels

[Clemens Ladisch]

Arthur Marsh wrote:
> OK, I applied this patch.
> 
> When the MIDI file was playing:
> I still experienced some slow-down and speed-up under heavy load.

Is "some" less than previously?

It shouldn't be possible to get a speed-up; this looks as if your
computer's clock is not stable.  Are you using an NTP daemon?

What kind of heave load is this?  Does the same happen if you execute
"yes | tail" in a shell?


Regards,
Clemens

Re: MIDI playback not keeping steady time with recent kernels

[Arthur Marsh]

Clemens Ladisch wrote, on 09/02/11 02:10:
> Arthur Marsh wrote:
>> OK, I applied this patch.
>>
>> When the MIDI file was playing:
>> I still experienced some slow-down and speed-up under heavy load.
>
> Is "some" less than previously?

The amount of slow-down appears to be less than previously.

>
> It shouldn't be possible to get a speed-up; this looks as if your
> computer's clock is not stable.  Are you using an NTP daemon?

To clarify, the speed-up is back to original tempo, and yes I'm using an 
NTP daemon. There has been an issue of the pc not keeping accurate time 
under GNU/Linux even with ntpd running and using an NTP server a few 
hops away.

>
> What kind of heave load is this?  Does the same happen if you execute
> "yes | tail" in a shell?

The load when I experienced this problem was about 4 or 5, and mainly 
seemed to be tied to activities that caused swapping (e.g. running 
aptitude -u when other applications were using all available memory and 
some swap).

After quitting some applications so that there was no swapping going on 
(kswapd0 showing 0.0 cpu), the MIDI file played fine, even with 
"yes|tail" running.

Adding aptitude -u to the mix, which resulted in kswapd0 running at 4 to 
10 percent cpu, caused a slow-down.


>
>
> Regards,
> Clemens
>

Thanks again,

Arthur.