pcm_meter.c issue at s16_update

[Pavel Hofman]

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.

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.