request for beta2 announcement input

Eero Tamminen oak at helsinkinet.fi
Sun Apr 18 10:18:37 BST 2010


Hi,

On Saturday 17 April 2010, Jarno Suni wrote:
> Well, it has happened that pulseaudio does something additional,
> supposedly useless:
> https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/207135
> But it is marked as fixed, so hopefully in Lucid there is no such
> problem.

According to this bug, the problem was both in pulseaudio & kernel/ALSA
and both need to be fixed for the issue to go away.

I'm not sure, but in the Pulseaudio case the fix seemed to be disabling
glitch-free[1] playback until ALSA audio drivers and distros in general
work well enough with it.

[1] see:
	https://fedoraproject.org/wiki/Features/GlitchFreeAudio
	http://0pointer.de/blog/projects/pulse-glitch-free.html


> Still, If I have understood right, low latency requested by some
> programs results in more CPU usage, when using pulseaudio.

According the stuff that can be found by following links in that bug, the
cause for that is that Ubuntu kernels have much higher latencies than Fedora
kernels (pulseaudio comes from Fedora).  Some of the reasons for the latency
issues are:
- CONFIG_HZ is set much lower (than kernel default)
- crappy (proprietary?) drivers that break latency when using
  the voluntary pre-empt kernel option

This is for Ubuntu desktop kernels.  If one starts with server install, you
get a server kernel which doesn't have pre-empt enabled which causes even
worse latencies (servers care more about throughput than latency).
I ddon't know which kernel comes from the alternate install.


The issue with is that when Pulseaudio notices that latency was too
large (for the sound buffer sizes which ALSA allows), it needs to wake up
more often.  If the latencies are larger than the ALSA buffer sizes, it will
wake up _really_ often and therefore consumes a lot of CPU too...

For more details, see:
https://tango.0pointer.de/pipermail/pulseaudio-discuss/2009-February/003150.html
https://tango.0pointer.de/pipermail/pulseaudio-discuss/2009-February/003168.html



	- Eero

PS. With ALSA there seems to be also a problem that it seems somewhat
unmaintained. Their alsa-project.org site has been taken over by some
www-address parking site(!?!).  The unofficial site seems still to work
though:
	http://alsa.opensrc.org/index.php/Main_Page



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