(In reply to Takashi Iwai from comment #5) > I checked 4.2.3 on OBS Kernel:stable, and it works. Please give it a try. He likely has some systemd group scheduling enabled (voluntarily, or because systemd ignored disabled user@0.service), in which case trying to insert an rt task into a cgroup with no rt_runtime will fail, as will trying to change the class of a task in such a cgroup to rt class.