Re: [RFC PATCH v5 20/29] sched/deadline: Allow deeper hierarchies of RT cgroups

[Yuri Andriaccio]

Hello,

I've been thinking and experimenting with some of the ideas for the rt 
controller, and I've come up with the following interface, keeping 
everything in the standard cpu controller:

- cpu.rt.max <runtime_us> <period_us>
  Sets the bandwidth reserved to the hierarchy that has that specific 
cgroup as root, but does
  not set any deadline servers.
  The default value for this file is '0 0'.
- cpu.rt.min <runtime_us | 'root'> <period_us>
  If the runtime part is equal to 'root', the tasks are scheduled on 
the root runqueue.
  If the runtime is equal to zero, no FIFO/RR tasks can be scheduled.
  If the runtime is > zero, FIFO/RR tasks are scheduled under 
reservation/HCBS.
  This file is not available in the root cgroup, as it does not make 
use of dl-servers,
  rather only reserves the total bandwidth for the hierarchy.
  The default value for this file is 'root 0', meaning that tasks in 
this cgroups are
  by default scheduled on the root runqueue.

Of course you can imagine that all the admission tests have been updated 
accordingly, as an example a cgroups rt.max bw must be >= than the sum 
of the rt.max bws of its children + its rt.min bw. I'm also skipping 
some details which are only meaningful if we decide to adopt this solution.

What do you think of this interface?

Thanks,
Yuri