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    SubjectRe: [tip:sched/core] sched: Fix load avg vs cpu-hotplug

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Tue, 2012-09-04 at 11:43 -0700, tip-bot for Peter Zijlstra wrote:
    > > Commit-ID: f319da0c6894fcf55e21320e40506418a2aad629
    > > Gitweb: http://git.kernel.org/tip/f319da0c6894fcf55e21320e40506418a2aad629
    > > Author: Peter Zijlstra <peterz@infradead.org>
    > > AuthorDate: Mon, 20 Aug 2012 11:26:57 +0200
    > > Committer: Ingo Molnar <mingo@kernel.org>
    > > CommitDate: Tue, 4 Sep 2012 14:30:18 +0200
    > >
    > > sched: Fix load avg vs cpu-hotplug
    > >
    > > Rabik and Paul reported two different issues related to the same few
    > > lines of code.
    > >
    > > Rabik's issue is that the nr_uninterruptible migration code is wrong in
    > > that he sees artifacts due to this (Rabik please do expand in more
    > > detail).
    > >
    > > Paul's issue is that this code as it stands relies on us using
    > > stop_machine() for unplug, we all would like to remove this assumption
    > > so that eventually we can remove this stop_machine() usage altogether.
    > >
    > > The only reason we'd have to migrate nr_uninterruptible is so that we
    > > could use for_each_online_cpu() loops in favour of
    > > for_each_possible_cpu() loops, however since nr_uninterruptible() is the
    > > only such loop and its using possible lets not bother at all.
    > >
    > > The problem Rabik sees is (probably) caused by the fact that by
    > > migrating nr_uninterruptible we screw rq->calc_load_active for both rqs
    > > involved.
    > >
    > > So don't bother with fancy migration schemes (meaning we now have to
    > > keep using for_each_possible_cpu()) and instead fold any nr_active delta
    > > after we migrate all tasks away to make sure we don't have any skewed
    > > nr_active accounting.
    >
    > Oh argh.. this patch isn't actually right.. I actually removed
    > it from my series but forgot to update the tarball.

    Sigh.

    > Ingo can you still make it go away or should I do a delta?

    Please do a delta.

    Thanks,

    Ingo


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