[linux-audio-dev] xruns

[Florian Schmidt]

On Wed, 2 Nov 2005 15:30:49 +0100
conrad berhörster <conrad.berhoerster at gmx.de> wrote:

> Hello list, 
> well i try to understand the reason of xruns. when will they appear? 
> 
> for me it's curious, that , while copy a big file (> 50MB ) or many small one, 
> there are xruns. so, it seems, that it has nothing to do with the soundcard 
> buffers. 
> 
> any comments? 

Well, yeah. First of all your question is very unprecise. I will try to
guess the blanks.

1) you are probably talking about jackd as most other alsa apps don't
even report their xruns

2) you are probably not running a realtime preemption or other low
latency kernel

3) you are not running jack with the realtime flag (-R)

The reason for an xrun is basically:

The process consuming/producing audio did not do this fast enough (Audio
is processed in chunks and you have the time equivalent to one chunk of
audio to produce/consume it).

This can have many reasons:

- you ask too much of your computer (like the computations involved are
simply too complex). This would produce a constant stream of xruns
though. I suppose you probably see much less then 1 per
periodsize/samplerate sec.

- this is the more probable reason: Some other process on your system
kept your audio producing/consuming process from doing its thang.

This second one can be remedied by changing step 2 and 3 above. 

There's two more potential reasons which i can think of right now:

4) your jack tmpfs is not mounted on a tmpfs or shmfs filesystem

5) NPTL hell (google for this one)

Have fun,
Flo






-- 
Palimm Palimm!
http://tapas.affenbande.org