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

[luca abeni <luca.abeni@santannapisa.it>]

Hi all,

On Thu, 7 May 2026 12:53:31 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
[...]
> > - This has the same problem with cgroup1's rt cgroup sched support
> > where there is no way to have a permissive default configuration,
> > which means that users who don't really care about distributing rt
> > shares hierarchically would get blocked from running rt processes
> > by default, which basically forces distros to disable rt cgroup
> > sched support. This is not new but it'd be a shame to put in all
> > the work and the end result is that most people don't even have
> > access to the feature.  
> 
> Right, but cgroup-v2 allows enabling/disabling specific controllers
> for a (sub)-hierarchy, right? So if the controller is not enabled (by
> default), it will fall back to putting the tasks in whatever parent
> does have it on, and by default the root group would have and would
> accept tasks.

We are discussing this issue with Yuri, and we have a doubt: if we
disable the RT-CPU controller for a cgroup, would it be possible to
enable it for its children?
(In other words: if we want the RT-CPU controller to be enabled for
some "leaf" cgroups, we need to enable it for their parents, right?)



			Thanks,
				Luca