Low latency kernel in Karmic to help with PulseAudio?

Daniel T Chen seven.steps at gmail.com
Wed May 6 06:15:24 BST 2009


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On Wed, 6 May 2009, Vishal Rao wrote:

> Is there going to be discussion during UDS amongst yourselves (devs) about enabling low-latency for Karmic as well?

Yes.

> See this mailing list post by Lennart of PulseAudio/Fedora fame:
> https://tango.0pointer.de/pipermail/pulseaudio-discuss/2009-February/003150.html

One thing to keep in mind (that I've raised to other developers) is that 
Ubuntu tends to release with slightly older versions of software in the 
audio stack. This tends to complicate development and troubleshooting of 
audio problems. FeatureFreeze has been early enough to prevent updating 
ALSA (think kernelspace and userspace sync) and PulseAudio, both of which 
contribute quite heavily to user experience.

For Hardy, this was a significant problem. New versions of ALSA necessary 
for improved PulseAudio integration were released immediately after 8.04 
released. The best that could have been done would have been to configure 
PulseAudio to use dmix and dsnoop devices to work around the massive 
breakage that ensued. Of course that approach runs afoul of Lennart's 
strident recommendations that only hw be used.

For Jaunty, we again encountered the situation where significant linux 
patches were necessary to prevent disastrous regressions from Intrepid's 
user experience, and of course these patches were developed and tested 
extremely late in the 9.04 cycle. Testing and tweaking of these fixes is 
ongoing (see the linux SRU), with many indications that all levels of the 
stack need to be realigned to resolve PulseAudio's behaviour.

(It's worth noting that several pieces need to be aligned in Karmic:
  linux; - needs to remain synced with
  alsa-lib;
  alsa-plugins;
  pulseaudio)

The Karmic development schedule has some points at which these syncs can 
be evaluated, and hopefully 9.10 will have the necessary pieces in place.

Once there are devoted developers for these tasks, the user experience 
should improve noticeably.

Dan
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