[systemd-devel] [lennart at kemper.freedesktop.org: [systemd-commits] src/pam-module.c]

[Andrey Borzenkov]

On Mon, Feb 14, 2011 at 6:12 AM, fykcee1 at gmail.com <fykcee1 at gmail.com> wrote:
> Hi Lennart,
> Thanks for the explanation.
> IMHO, To re-enable user session 'cpu' sorting:
> a) Desktop distributions disable GROUP_RT in the kernel, then no
> rt_bandwidth, all RT-apps can be fully administrated under rtkit.
> Or b) cpu cgroup controller should default make sub-cgroups share
> rt_bandwidth with their parent.

RT is about determinism. You need to ensure that task will be able to
respond in fixed time. If you allow arbitrary, unknown in advance,
number of tasks share the same limited CPU share, you simply kill
determinism.

Personally I think that RT should be restricted to limited number of
tasks that are known in advance; then it is responsibility of
administrator to allocate their CPU share according to requirements.

>
> 2011/2/14 Lennart Poettering <lennart at poettering.net>
>>
>>
>> I am not aware of any typical daemon we ship that would use RT
>> scheduling hence we are keeping the default 'cpu' cgroup sorting for
>> system daemons enabled. However user applications are more likely to use
>> RT (for example PA does) and hence we have disabled this for sessions
>> for now.
>>

and for reasons outlined above I think that either PA should not
require RT to run, or we need dedicated system wide PA daemon that can
be made RT :)