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

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Message-ID: <YpCPjP2jJgLzCo1C@slm.duckdns.org>
Date:   Thu, 26 May 2022 22:45:00 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Waiman Long <longman@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        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

Hello,

On Fri, May 27, 2022 at 10:30:18AM +0200, Juri Lelli wrote:
> FWIW, I was under the impression that this would nicely fit along the
> side of other feaures towards implenting dynamic isolation of CPUs (say
> https://lore.kernel.org/lkml/20220510153413.400020-1-longman@redhat.com/
> for example). Wouldn't be awkward to have to poke different places to
> achieve isolation at runtime?

So, it were just being part of the isolated domain thing, it would make
sense, but as a separate flag which isn't hierarchical, it's weird to put it
there.

> Also, I wonder if a proc/sys interface might be problematic for certain
> middleware that is substantially based on using cgroups. I'll try to ask
> around. :)

There is a downside to making a feature a part of cpuset in that it makes
cgroup usage mandatory. This is fine for something which benefits from
hierarchical organization but it is weird to require building cgroup
hierarchy for straight-forward system-wide features.

Thanks.

-- 
tejun