[LAU] RT_GROUP_SCHED kernel option makes JACK unusable in Ubuntu Natty

Andy Whitcroft apw at canonical.com
Tue Mar 15 15:16:52 UTC 2011

On Wed, Dec 15, 2010 at 01:07:23PM +0100, torbenh wrote:
> On Tue, Dec 14, 2010 at 11:46:55PM -0500, Ronan Jouchet wrote:
> > On 10-12-14 11:39 PM, Daniel Chen wrote:
> > >On Tue, Dec 14, 2010 at 11:33 PM, Ronan Jouchet<ronan at jouchet.fr>  wrote:
> > >>I confirm 2.6.37-9.22~ppa1 from abogani PPA (RT_GROUP_SCHED disabled)
> > >>works fine.
> > >>
> > >>I will leave the decision to Alessio (or somebody else from the kernel
> > >>team) to close or not
> > >>https://bugs.launchpad.net/ubuntu/+source/linux/+bug/690010 , since a
> > >>proper solution implementing cgroups management may be preferable and
> > >>implementable.
> > >
> > >As Paul alludes to, changing this Ubuntu kernel config option doesn't
> > >resolve the real issue, and I wouldn't be keen on changing the option
> > >that clearly works for other applications.
> how does the option work for other applications ?
> this statement looks like you dont understand what this is all about :(
> > >
> > >-Dan
> > 
> > 101% agreed, if this option is here to stay (and it seems to be), a
> > "proper solution implementing cgroups management" would be
> > preferable
> in this case you need to put the relevant stuff into /etc/cgconfig.conf
> in order to make jack clients obtain their share of rt-cputime they
> need to get moved into a cgroup which has some rt-bandwidth setup.
> the big problem is that the cgroup where the process needs to be moved
> to depends on how /etc/cgconfig.conf is setup.
> libjack can not find this out.
> we could provide hooks, which allow distro specific hacks.
> but they would break if users start to mess with the cgroup layout.
> userspace is not ready for this kernel option. this is like turning off
> devfs without having udevd in place.
> i always thought ubuntu was about making things easy for the user.
> regarding jack, ubuntu has quite a big track record of making things hard
> for the users.

It is possible that this has been resolved upstream, fixed by the commit
below.  Which (to my reading) says that in the face of autogroups an RT
task is shifted over to the rootcg.  This fix would have been in all
2.6.38 based Natty kernels.  I would be interested to know if this does
resolve Jack's issues:

  commit f44937718ce3b8360f72f6c68c9481712517a867
  Author: Mike Galbraith <efault at gmx.de>
  Date:   Thu Jan 13 04:54:50 2011 +0100

    sched, autogroup: Fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure


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