pcm_meter.c issue at s16_update

[Takashi Iwai]

On Tue, 28 Jul 2020 18:46:00 +0200,
Pavel Hofman wrote:
> 
> 
> Dne 26. 07. 20 v 20:20 Pavel Hofman napsal(a):
> > Hi,
> > 
> > I am debugging the following problem with the PCM METER API:
> > 
> > An application with meter/scope configured in .asoundrc hits a high CPU
> > load sometimes when a new playback stream is opened. E.g. in MPD when
> > opening a new radio stream. The 100% CPU core load takes tens of seconds.
> > ...........
> > 
> > TL;DR: at decrease of [status.appl_ptr - status.delay] between
> > consequent runs the size of buffer to convert by the built-in s16 scope
> > is set from usual 100s to huge value of pcm->boundary (1.5G), causing a
> > very long processing at 100% core load.
> > 
> > The debug around the event looks like this, suddenly meter->now drops down:
> > 
> > s16_update 1: meter->now 2567498, s16->old 2566593, size 905
> > s16_update 1: meter->now 2568401, s16->old 2567498, size 903
> > s16_update 1: meter->now 20786, s16->old 20786, size 0
> > s16_update 1: meter->now 1065, s16->old 20786, size -19721
> > s16_update 1: meter->now 24839, s16->old 24838, size 1
> > s16_update 1: meter->now 701, s16->old 24839, size -24138
> > s16_update 1: meter->now 1253162, s16->old 701, size 1252461
> > s16_update 1: meter->now 1255148, s16->old 1253162, size 1986
> > 
> > ..........
> > 
> > s16_update 1: meter->now 11136, s16->old 10261, size 875
> > s16_update 1: meter->now 22525, s16->old 22524, size 1
> > s16_update 1: meter->now 963, s16->old 22525, size -21562
> > s16_update 1: meter->now 1270914, s16->old 963, size 1269951
> > s16_update 1: meter->now 1272917, s16->old 1270914, size 2003
> > 
> 
> I think the problem is that s16->old is not reset when status.appl_ptr
> is zeroed and starts running again. There is a call
> 
> static void s16_reset(snd_pcm_scope_t *scope)
> {
> 	snd_pcm_scope_s16_t *s16 = scope->private_data;
> 	snd_pcm_meter_t *meter = s16->pcm->private_data;
> 	s16->old = meter->now;
> }
> 
> but I do not know when this method is called and whether the meter->now
> is already assigned to the newly zeroed status.appl_ptr.

Would adding atomic_add(&meter->reset, 1) in snd_pcm_meter_reset()
help?


Takashi


> 
> Please at which method should I reset s16->old = 0?
> * s16_reset
> * s16_enable
> * s16_start
> * snd_pcm_scope_s16_open
> 
> 
> Thanks a lot for any help,
> 
> Pavel.
>