[systemd-devel] cgroupsv2 and realtime processes

[Michał Zegan]

Hello,

This is more of a kernel than systemd question but I am not subscribed 
to any kernel ml and I assume systemd people should know the answer.

I have kernel 5.17 on archlinux. 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.

Is that still true?

I ask because what I currently have is that things like pipewire sound 
server are running on the system, and some of pipewire's threads do have 
realtime priority, it seems.

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?

The user.slice which contains, indirectly, the pipewire cgroup 
(pipewire.service) doesn't have the cpu controller enabled, but I assume 
that shouldn't make a difference.

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