[systemd-devel] cgroupsv2 and realtime processes

[Michal Koutný]

On Mon, Jun 06, 2022 at 04:54:03PM +0200, Michał Zegan <webczat at outlook.com> wrote:
> this note pointed to in the readme is quite cgroups v1 specific, I believe
> what it describes was true in v1, and v2 does not have any capability to
> control realtime processes in non root cgroups if I read correctly.

Yes. And it extends to v2 too where there are even no userspace knobs to
configure the RT attributes.

Therefore it works [1] with CONFIG_RT_GROUP_SCHED unset since RT
processes remain in the root cgroup (it's an implementation detail you
won't see from /proc/$pid/cgroup, where is still the regular process
membership).
To prevent confusion -- this applies only to processes (threads) with RT
policy and from all other perspectives these processes (threads) are
still in the listed cgroup.

Does that explain what you were after?

Michal

[1] Unless your goal is to control per-cgroup RT attributes. I
understood you just wanted to be able to place RT processes into
non-root cgroups.