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

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Date:   Tue, 29 Aug 2023 11:24:24 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.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 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.

> 
> 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.