The following is an excerpt from cgroups(7):
The cgroups v2 "cpu" controller and realtime processes
As at Linux 4.15, the cgroups v2 cpu controller does not
support control
of realtime processes, and the controller can be enabled
in the root
cgroup only if all realtime threads are in the root cgroup. (If
there are
realtime processes in nonroot cgroups, then a write(2) of
the string
"+cpu" to the cgroup.subtree_control file fails with the
error EINVAL.
However, on some systems, systemd(1) places certain realtime
processes in
nonroot cgroups in the v2 hierarchy. On such systems, these
processes
must first be moved to the root cgroup before the cpu
controller can be
enabled.
At the end of the sentence ending EINVAL, there should be a close
parenthesis after the period.
Best,
--Mike Weilgart
Vertical Sysadmin, Inc.
