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

[Peter Zijlstra <peterz@infradead.org>]

On Thu, May 07, 2026 at 05:03:41PM +0200, Juri Lelli wrote:
> 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?

Exactly!