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

[fykcee1 at gmail.com]

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.
Internally, kernel uses two separate hierarchies for NORMAL and RT
processes, current logic should be changed as: a new cgroup with a cpu
controller will add a new level in 'NORMAL hierarchy', but not touch
'RThierarchy' unless set sched_rt_runtime_us.


2011/2/14 Lennart Poettering <lennart at poettering.net>

> On Fri, 11.02.11 10:30, fykcee1 at gmail.com (fykcee1 at gmail.com) wrote:
>
> > Hi Lennart, Andrey,
> >
> > Some questions about the discuss:
> >   1. Does systemd re-enable sorting user sessions into their own cgroups
> in
> > the 'cpu' hierarchy?
>
> No, we cannot reenable that before the cpu cgroup controller gets fixed.
>
> On current kernels doing this kind of sorting means practically that all
> processes we sort into a 'cpu' cgroup lose their capability to use RT
> scheduling.
>
> 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.
>
> >   2. AIUI, rtkit is a daemon used for doing RT-related privilege
> operations.
> > It doesn't spawn RT-threads. Am I right?
>
> It does use RT privs for the implementatin of the canary watchdog.
>
> >   3. Does rtkit have related systemd service file? Does it run at its own
> > cgroup with controller=cpu? If yes, how does the cgroup receive
> > rt-bandwidth(period time, run time)?
>
> rtkit comes with a systemd unit file. In rtkit git this unit file
> ensures that rtkit is explicitly moved into the root "cpu" cgroup so
> that it can make use of RT scheduling -- if you so will rtkit is the one
> exception to what i mentioned above regarding no system daemons using
> RT.
>
> Lennart
>
> --
> Lennart Poettering - Red Hat, Inc.
>



-- 
Regards,

- cee1
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