Re: Polypaudio for Gnome 2.10, the next steps

[Lennart Poettering <mztabzr 0pointer de>]

On Tue, 23.11.04 08:20, Andy Balaam (andybalaam artificialworlds net) wrote:

> 
> My summary of the discussion so far is that there seem to be 2 options:
> 
> 1. Scrap esound and replace it with ALSA + a few bits.
> 
> Some people feel this is the way it "ought" to be done.  However, there 
> are problems with what appear to be bugs in alsalib, and new code would 
> need to be written to deal with sound cards that don't do mixing, and 
> remote desktops.

There's another issue with dmix which is very difficult to fix as I
see it: low latency playback. If you want to do that really well you
need to use SCHED_FIFO process scheduling (at least on current Linux
kernels). This is only available as root. Since dmix runs in the
process of the application which does audio playback, you'd have to
activate SCHED_FIFO for all user apps. However, this is a great
security risk, since every process that has SCHED_FIFO may effectively
freeze the machine. In contrast, when using polypaudio you can
activate this for the daemon process only. Polypaudio does its best to
prevent misuse of this feature. Since polypaudio's internal playback
buffering is exposed very flexibly to the client, it may make use of
this low latencies without being run with SCHED_FIFO as well. In
addition, the client may load special modules into the polypaudio
core, if the exposed buffering is not flexible enough.

I don't see how this could be fixed with dmix. 

Lennart

-- 
name { Lennart Poettering } loc { Hamburg - Germany }
mail { mzft (at) 0pointer (dot) de } gpg { 1A015CC4 }  
www { http://0pointer.de/lennart/ } icq# { 11060553 }