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Date: Sat, 3 Oct 2015 08:53:20 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: 4.2.2: NR_CPUS effectively being 1 bug
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On Fri, Oct 02, 2015 at 02:00:33PM -0700, Andrew Morton wrote:
> On Fri, 2 Oct 2015 23:46:59 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> 
> > FYI, I've upgraded from 4.1.7 to 4.2.1 (and retested with 4.2.2) and
> > everything is scheduled on 1 CPU out of 4 (i5 760).
> > 
> > 	$ sudo cat /proc/1/status | grep cpu -i
> > 	Cpus_allowed:   1
> > 	Cpus_allowed_list:      0
> > 
> > Every process inherits this tiny cpumask.
> 
> Sell the other CPUs on ebay?
> 
> I haven't seen such a report before - maybe it rings a bell with Peter
> & Ingo?

I think this is related to some NO_HZ_FULL quackery. People seem to have
enabled stuff they've really no sane reason for.