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Groups > linux.kernel > #1238847

Re: 4.2.2: NR_CPUS effectively being 1 bug

From Frederic Weisbecker <fweisbec@gmail.com>
Newsgroups linux.kernel
Subject Re: 4.2.2: NR_CPUS effectively being 1 bug
Date 2015-10-03 14:40 +0200
Message-ID <qfugz-1TL-31@gated-at.bofh.it> (permalink)
References (4 earlier) <qfqcW-4Ce-11@gated-at.bofh.it> <qfqcW-4Ce-19@gated-at.bofh.it> <qfqmC-4NE-11@gated-at.bofh.it> <qfqPE-5lm-17@gated-at.bofh.it> <qftNw-1lQ-25@gated-at.bofh.it>
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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.
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Thread

Re: 4.2.2: NR_CPUS effectively being 1 bug Andrew Morton <akpm@linux-foundation.org> - 2015-10-02 23:10 +0200
  Re: 4.2.2: NR_CPUS effectively being 1 bug Peter Zijlstra <peterz@infradead.org> - 2015-10-03 09:00 +0200
    Re: 4.2.2: NR_CPUS effectively being 1 bug Ingo Molnar <mingo@kernel.org> - 2015-10-03 09:40 +0200
      Re: 4.2.2: NR_CPUS effectively being 1 bug Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-03 10:20 +0200
        Re: 4.2.2: NR_CPUS effectively being 1 bug Ingo Molnar <mingo@kernel.org> - 2015-10-03 10:20 +0200
          Re: 4.2.2: NR_CPUS effectively being 1 bug Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-03 10:30 +0200
            Re: 4.2.2: NR_CPUS effectively being 1 bug Ingo Molnar <mingo@kernel.org> - 2015-10-03 11:00 +0200
              Re: 4.2.2: NR_CPUS effectively being 1 bug Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-03 14:10 +0200
                Re: 4.2.2: NR_CPUS effectively being 1 bug Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-03 14:40 +0200
                Re: 4.2.2: NR_CPUS effectively being 1 bug Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-03 14:50 +0200
        Re: 4.2.2: NR_CPUS effectively being 1 bug Alexey Dobriyan <adobriyan@gmail.com> - 2015-10-03 14:20 +0200
          Re: 4.2.2: NR_CPUS effectively being 1 bug Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-03 14:30 +0200

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