[systemd-devel] cgroupsv2 and realtime processes
Michal Koutný
mkoutny at suse.com
Mon Jun 6 14:02:34 UTC 2022
Hello Michał.
On Sun, Jun 05, 2022 at 03:28:23PM +0200, Michał Zegan <webczat at outlook.com> wrote:
> I have kernel 5.17 on archlinux.
How is your kernel configured wrt CONFIG_RT_GROUP_SCHED?
> Is that still true?
That depends :-)
> Yet, checking /proc/(pid)/cgroup states these processes are not in a root
> cgroup, yet the cpu controller is enabled on the root cgroup
> (/sys/fs/cgroup/cgroup.subtree_control lists "cpu" as one of the controllers
> and I see the interface files in children).
>
> Can anyone explain the situation?
With v2 and CONFIG_RT_GROUP_SCHED there's no way how to assign realtime
budgets to cgroups and therefore realtime tasks cannot run in them.
With !CONFIG_RT_GROUP_SCHED, there's (internally) only the root cgroup
for realtime tasks and things apparently work.
See also [1].
> <snip>
> The cgroupsv2 documentation states that cgroup cpu controller
> currently does not support realtime processes, so to enable it all
> realtime processes must be moved to root cgroup.
Will you send a docs patch with the CONFIG_RT_GROUP_SCHED reservation?
:-p
HTH,
Michal
[1] https://github.com/systemd/systemd/blob/369151c9c73b12fb7a88fc2b558499c2d4832982/README#L140
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