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Date: Sat, 3 Oct 2015 14:31:17 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@elte.hu>, Christoph Lameter <cl@linux.com>
Subject: Re: 4.2.2: NR_CPUS effectively being 1 bug
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On Sat, Oct 03, 2015 at 02:04:44PM +0200, Mike Galbraith wrote:
> On Sat, 2015-10-03 at 10:52 +0200, Ingo Molnar wrote:
> > Ok, looks like a patch with good intentions but bad effects. Mind sending a revert 
> > patch, changelogged, signed off?
> 
> No.  They know.

The reason for this patch is that NO_HZ_FULL is only useful on a CPU if no task
other than the desired one can be scheduled on it. Hence the cpu_isolated_map.

Only those who enable NO_HZ_FULL_ALL by accident do complain, not those who
really use it so far. At least it makes people realize their mistake.

That said I never liked that cpu_isolated_map. And some regular non-isolation
work may be needed to be done even on NO_HZ_FULL_ALL machines and it that
case we get screwed.

So I should revert that and defer that isolation work to explicit affinity
setting or cpusets.