home-assistant/supervisor#2593

This refs #1235

I tested the changes suggested by this PR in HAos and I could reproduce that at least docker has now enough cpu.rt_runtime_us resources assigned now:

# cat /sys/fs/cgroup/cpu/docker/cpu.rt_runtime_us
950000

However, the suggested change by @pvizeli in home-assistant/supervisor#2593 seems not be enough to get each container started by docker with enough real-time shares so that applications using sched_setscheduler() are able to run correctly. So even after using a supervisor developer build with the changes by home-assistant/supervisor#2593 and the new realtime option used in config.json of the add-on ends up in ...

# cat /sys/fs/cgroup/cpu/cpu.rt_runtime_us
0
# multimacd -l 0 -c
[...]
2021/02/21 18:55:42.923 <Warning> Could not set scheduling priority: Operation not permitted
2021/02/21 18:55:42.923 <Warning> Could not set scheduling priority: Operation not permitted
2021/02/21 18:55:42.923 <Warning> Could not set scheduling priority: Operation not permitted

Reviewing the changes suggested by home-assistant/supervisor#2593 it looks like only the --ulimit rtprio=99 option is added by the new realtime option when starting docker containers of add-ons. However, AFAIK the --cpu-rt-runtime=950000 option is also additionally required to get the cpu.rt_runtime_us cgroup raised also.

See https://docs.docker.com/config/containers/resource_constraints/#configure-the-realtime-scheduler

home-assistant/supervisor#2602

Need also an SUPERVISOR_CPU_RT=1 on the env @agners