linux-kernel - Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up at boot time

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Date:   Mon, 17 Jun 2019 17:59:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up
 at boot time

On Mon, Jun 10, 2019 at 05:24:32PM +1000, Nicholas Piggin wrote:
> Nicholas Piggin's on June 1, 2019 9:39 pm:
> > With the change to allow the boot CPU0 to be isolated, it is possible
> > to specify command line options that result in no housekeeping CPU
> > online at boot.
> > 
> > An 8 CPU system booted with "nohz_full=0-6 maxcpus=4", for example.
> > 
> > It is not easily possible at housekeeping init time to know all the
> > various SMP options that will result in an invalid configuration, so
> > this patch adds a sanity check after SMP init, to ensure that a
> > housekeeping CPU has been onlined.
> > 
> > The panic is undesirable, but it's better than the alternative of an
> > obscure non deterministic failure. The panic will reliably happen
> > when advanced parameters are used incorrectly.
> 
> Ping on this one? This should resolve Frederic's remaining objection
> to the series (at least until he solves it more generally).
> 
> As the series has already been merged, should we get this upstream
> before release?

I was hoping for feedback from Frederic, lacking that, I've queued it
now.