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Re: [tip:sched/core] sched: 'Annotate' migrate_tasks()

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On Sun, Sep 13, 2015 at 3:56 AM, tip-bot for Wanpeng Li
<tipbot@zytor.com> wrote:
> +               lockdep_unpin_lock(&rq->lock);
> +               raw_spin_unlock(&rq->lock);
> +               raw_spin_lock(&next->pi_lock);
> +               raw_spin_lock(&rq->lock);

So _if_ this is ever likely to be a performance-critical piece of
code, it might be worth doing

    if (!raw_spin_trylock(&next->pi_lock)) {
        .. do the above unlock and relock in the right order sequence ..
    }

to avoid doing that whole "unlock just to relock in the right order" thing.

That's particularly true in cases where dropping one of the locks can
necessitate re-doing some checks.

              Linus
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[tip:sched/core] sched: 'Annotate' migrate_tasks() tip-bot for Wanpeng Li <tipbot@zytor.com> - 2015-09-13 13:00 +0200
  Re: [tip:sched/core] sched: 'Annotate' migrate_tasks() Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-15 02:00 +0200
    Re: [tip:sched/core] sched: 'Annotate' migrate_tasks() Peter Zijlstra <peterz@infradead.org> - 2015-09-15 10:00 +0200

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