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

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Message-ID: <YpTDq6Z/+hp+CHwf@worktop.programming.kicks-ass.net>
Date:   Mon, 30 May 2022 15:16:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Juri Lelli <juri.lelli@...hat.com>, Tejun Heo <tj@...nel.org>,
        Waiman Long <longman@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Phil Auld <pauld@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        rcu@...r.kernel.org
Subject: Re: [RFC PATCH 4/4] cpuset: Support RCU-NOCB toggle on v2 root
 partitions

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.