[ronan at jouchet.fr: [Jack-Devel] RT_GROUP_SCHED kernel option makes JACK unusable in Ubuntu Natty]

[Adrian Knoth]

Hi!

Just for the LP bug number. I guess we now have enough information to
participate in any upcoming discussion. ;)

----- Forwarded message from Ronan Jouchet <ronan at jouchet.fr> -----

Date: Mon, 13 Dec 2010 23:34:21 -0500
From: Ronan Jouchet <ronan at jouchet.fr>
To: ubuntu-studio-devel at lists.ubuntu.com, jack-devel at lists.jackaudio.org,
	kernel-team at lists.ubuntu.com,
	Alessio Igor Bogani <abogani at ubuntu.com>
Subject: [Jack-Devel] RT_GROUP_SCHED kernel option makes JACK unusable in
	Ubuntu Natty

Hi Ubuntustudio-devel, Ubuntu-kernel, JACK-devel, Alessio,

After talking with adi in #ffado and las in #jack, it appears that Natty's 
kernel needs adjustment to be usable for audio work. Currently the kernel 
flavors shipped by Ubuntu have the RT_GROUP_SCHED option activated, which 
makes JACK unusable (las put up http://jackaudio.org/linux_group_sched to 
sum up the situation).

*Until this problem is solved, JACK is unusable under Natty*. Las  
mentioned several solutions:
  0. Disabling RT_GROUP_SCHED for all kernels
1. Disabling RT_GROUP_SCHED for the kernel targeting audio users  
(-lowlatency, currently living in abogani's PPA)
2. Set up a cgroup and invoke JACK and every client from a shell script 
that joins the cgroup first
3. Use cgrules.conf to at least put processes into the right group by  
default
4. Use Ubuntu's specific mechanism to put user tasks into a RT-enabled 
cgroup

Quoting las: "(1) is the desirable option; (2) would be next and (3) would 
be hard, because it would enforce 'application <foobar> always run in the 
<bazbar> cgroup' which is not really very useful or correct". (0) may also 
be considered since this kernel option is apparently very specialized for 
embedded systems and doesn't make sense for a desktop distro.

Which path should be followed is beyond my knowledge. I just hope this  
discussion will pave the way to a usable audio stack in Natty.

Resources:
  LP bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/690010
  IRC : #jack, #ubuntustudio,  #ubuntustudio-devel
  IRC log of my discussion with las: http://pastebin.com/2yw7aPhr

All the best,

-- 
Ronan Jouchet
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----- End forwarded message -----

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