linux-kernel - Re: [PATCH] rcutorture: Traverse possible cpu to set maxcpu in rcu_nocb

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Message-ID: <7ca81dd6-af72-4345-9689-a1ef7dadfa95@paulmck-laptop>
Date:   Tue, 29 Aug 2023 05:38:54 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Z qiang <qiang.zhang1211@...il.com>,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [PATCH] rcutorture: Traverse possible cpu to set maxcpu in
 rcu_nocb_toggle()

On Tue, Aug 29, 2023 at 11:24:24AM +0200, Frederic Weisbecker wrote:
> On Mon, Aug 28, 2023 at 05:51:09PM -0400, Joel Fernandes wrote:
> > I think the issue is the loop later in the function does
> > not try to toggle cpus that came online too late.
> > 
> > So it does not test offloading on all CPUs just because max got updated too
> > late.
> 
> Right, and therefore for_each_possible_cpu() or for_each_present_cpu()
> should be fine to iterate since it's ok to try to toggle an offline CPU.

OK, so I will accept the original patch which did just that.

Thank you!

I recently got burned by lack of workqueues on a not-yet-onlined CPU,
hence my questions here.  ;-)

							Thanx, Paul

> > One fix could be to periodically check in the loop if a new cpu at maxcpu + 1
> > ever got onlined. If it did, update the maxcpu.
> 
> Is it worth the complication though?
> 
> Thanks.
> 
> > 
> > Thanks.
> > 
> > 
> > > 
> > > Thanks.