linux-kernel - Re: [PATCH 5/6] rcu/nocb: Allow empty "rcu

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Date:   Thu, 25 Nov 2021 14:28:53 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 5/6] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter

On Wed, Nov 24, 2021 at 08:41:32PM -0800, Yury Norov wrote:
> On Wed, Nov 24, 2021 at 04:47:20PM -0800, Paul E. McKenney wrote:
> > On Tue, Nov 23, 2021 at 01:37:07AM +0100, Frederic Weisbecker wrote:
> > > If a user wants to boot without any CPU in offloaded mode initially but
> > > with the possibility to offload them later using cpusets, provide a way
> > > to simply pass an empty "rcu_nocbs" kernel parameter which will enforce
> > > the creation of dormant nocb kthreads.
> > 
> > Huh.  This would have been a use for Yury Norov's "none" bitmask
> > specifier.  ;-)
> > 
> > I pulled this one in with the usual wordsmithing.
> > 
> > 							Thanx, Paul
> 
> I think 'rcu_nocbs=,' should work as 'none'. But I admit that it looks
> awkward. The following patch adds clear 'none' semantics to the parser.
> If you like it, I think you may drop non-documentation part of this
> patch.

I don't have real objection, but I fear that "rcu_nocbs=none" might be
interpretated as rcu_nocbs is entirely deactivated, whereas "rcu_nocbs"
alone makes it clear that we are turning something on.

We can support both though.

Thanks.