Tuning the system for jackd

[Free Ekanayaka <free@agnula.org>]

Hi all,

I'm re-styling the demudi tasks packages,  which I'd like to upload to
Debian in the near future.  One  of them it's called demudi-config and
it's haevily based on  the debian-edu-config package. It uses cfengine
to customize configuration files in a consistent manner.

As already discussed, we are going to drop the demudi specific version
of the jack package, and rely on the debian one.

I was  wandering  about which  tunings are  needed to  the enhance the
performance of jackd, and whether  they should be accomplished through
the demudi-config task or directly with jackd.

The ones that come to my mind are:

1) Turn on low latency:

   echo 1 > /proc/sys/kernel/lowlatency

   This assumes a patched  2.4 kernel, which  AFAIK is not the case of
   the official Debian kernel.

   I don't know whether the 2.6 series need such tuning too..

2) Setuid the   jackstart    binary. This  can   be  accomplished  via
   dpkg-statoverride (as suggested in the README.Debian of jackd), but
   I'm not sure whether the best solution is:

   a. Add debconf support to the jackd package and ask a question, for
   example  "Do you want  jackstart  setuid?", if  the  the answer  is
   positive    the    postinst   script  takes     care   of   running
   dpkg-statoverride.  In  this case  the demudi-config  package would
   just inject the appropriate value in the debconf database.

   b.  Do a. but through  the demudi-config package, maybe without the
   question, as we assume a positive answer.

   c.  Do not  setuid the jackstart binary, but  rather  prepare a 2.6
   kernel for DeMuDi  (I'm assuming that  Debian is not going to adopt
   such  patch  in the  short  term),  using the Jack  O'Quin's kernel
   module.  The demudi-config package could make sure that such module
   is loaded in the correct  way and ask  which users should belong to
   the audio group.

3) Mount /tmp as a tmpfs, adding the line

   none	/tmp tmpfs defaults 0 0

   to fstab. Again this can  be accomplished both inside demudi-config
   and inside jackd and I'm not sure which place is better.

4) Write a ~/.asoundrc file  (for users in the  audio group).  I don't
   know if  this  is really necessary,  but it  can be accomplished by
   demudi-config.

Nothing more comes to my mind by now..

Cheers,

Free