Re: [RFC PATCH 4/4] cpuset: Support RCU-NOCB toggle on v2 root partitions

[Frederic Weisbecker <frederic@kernel.org>]

On Mon, May 30, 2022 at 03:16:27PM +0200, Peter Zijlstra wrote:
> On Mon, May 30, 2022 at 12:56:50PM +0200, Frederic Weisbecker wrote:
> 
> > > This is ABI, you can't walk back on it. I would suggest starting with an
> > > 'all feature' isolation. Only if there's real demand for something more
> > > fine-grained add that on top. Simple first etc.
> > 
> > That's actually my worry. If we start with an all in one ABI, how do we later
> > mix that up with more finegrained features? Like what will be the behaviour of:
> > 
> > cpuset.isolation.rcu_nocb = 0
> > cpuset.isolation.all = 1
> 
> Well clearly that doesn't make sense. I was more thinking along the
> lines of cgroup.subtree_control, where instead all features are enabled
> by default.
> 
> But only if there's a real usecase, otherwise there's no point in
> providing such knobs.

That makes sense. So there would be a simple cpuset.isolation that can
be either 1 or 0 where 1 has all possible isolation stuff on. Then
if the need arises we can provide more tuning through a new specific
cgroup controller, right?

If so that sounds good to me.