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

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Message-ID: <9e44bb00-955a-dbc6-a863-be649e0c701f@redhat.com>
Date:   Thu, 26 May 2022 20:28:43 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.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 5/26/22 19:02, Tejun Heo wrote:
> On Fri, May 27, 2022 at 12:51:41AM +0200, Frederic Weisbecker wrote:
>>> Does it even make sense to make this hierarchical? What's wrong with a
>>> cpumask under sys/ or proc/?
>> I'm usually told that cpusets is the current place where CPU attributes are
>> supposed to go. I personally don't mind much /sys either even though cpusets
>> looks like a more flexible way to partition CPUs with properties and tasks
>> placement altogether...
> Yeah, I mean, if it's hierarchical, it's the right place but I have a hard
> time seeing anything hierarchical with this one. Somebody just has to know
> which cpus are up for rcu processing and which aren't. Waiman, what do you
> think?

I am thinking along the line that it will not be hierarchical. However, 
cpuset can be useful if we want to have multiple isolated partitions 
underneath the top cpuset with different isolation attributes, but no 
more sub-isolated partition with sub-attributes underneath them. IOW, we 
can only set them at the first level under top_cpuset. Will that be useful?

Cheers,
Longman