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

[Juri Lelli <juri.lelli@redhat.com>]

On 07/05/26 12:53, Peter Zijlstra wrote:
> On Tue, May 05, 2026 at 09:56:58AM -1000, Tejun Heo wrote:

...

> > - However, the cpu controller is a threaded controller which means that it
> >   can have threaded sub-hierarchy where the no-internal-process rule doesn't
> >   apply. This was created explicitly for cpu controller. The proposed change
> >   blocks it effectively forcing cpu controller into regular domain
> >   controller behavior subject to no-internal-process rule. Note these are
> >   enforced at controller granularity and this means that users who use the
> >   threaded mode will be forced to pick between the two.
> 
> Right... this then means we need two controls, one to do hierarchical
> bandwidth distribution, and one to assign bandwidth to the internal
> group -- which is then subject to its own bandwidth distribution
> constraint.
> 
> This might be a little confusing, but there is no way around that
> AFAICT.

Just to check if I'm following, you are thinking something like below?

groupA/
  cpu.rt.max = "50 50 100"       <- 0.5 from root
  cpu.rt.internal = "20 20 100"  <- 0.2 from groupA for threads at this
                                        level
  + threadA                               <
  + threadB                               <
  +- group1/
       cpu.rt.max = "30 30 100"  <- 0.3 from groupA
       + threadC

And we still keep it flat, so 2 dl-entities (per CPU), one handles
threads at groupA level and the other threads inside group1?

Thanks,
Juri