[linux-audio-dev] ALSA performance issues?

Mario Lang mlang at delysid.org
Thu Dec 21 14:40:30 UTC 2006


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.

This is a bit strange, isn't it.  OSS-emulation actually uses the same
kernel code to access the actual hardware.  I am just very vaguely
familiar with the whole ALSA architecture, but it feels as if
the problem here actually lies inside the user-space alsa libraries?

Did anyone ever see such an effect, and investigate more closely
what is the reason for the difference?
  Mario | Debian Developer <URL:http://debian.org/>
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