[linux-audio-dev] ALSA performance issues?

Mario Lang mlang at delysid.org
Sat Dec 23 13:08:23 UTC 2006

"Clemens Ladisch" <cladisch at fastmail.net> writes:

> Mario Lang wrote:
>> I just tried to get sound working on a LinkSys NSLU2 (ARM) running
>> Debian Etch using a USB sound card.
>> What I discovered I find pretty strange, and would like to know some
>> more details.  Apparently, all ALSA native clients don't
>> manage to play sound click-free, they actually have underruns all the
>> time.  However, if I use OSS (via the snd-pcm-oss module) and set
>> libao to use the oss driver, I get perfect playback with about
>> 20% CPU use at maxiumum by the user-space app playing/decoding files.
> Does the same happen when ALSA clients play to device "hw:0" as
> opposed to the default dmix device?

Excuse my ignorance please, but how do I reliably determine
if dmix is the default device?  For instance, ogg123, which uses libao,
only offers -o card:N and such, but no -o device:"string", so
I am kind of wondering if libao clients do perhaps always play on a
hw device?  I've tried to decipher the configuration in /usr/share/alsa,
but I didn't really come far.  dmix is definitely defined there, but
how do I know it is the default?

In any case, so far, playback only works through alsa oss emulation.
native alsa just underuns like hell.


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