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Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
Date 2016-06-15 20:50 +0200
Message-ID <rKo30-69o-19@gated-at.bofh.it> (permalink)
References <rK5jH-2zl-5@gated-at.bofh.it> <rK5jH-2zl-3@gated-at.bofh.it> <rKmkx-52w-7@gated-at.bofh.it> <rKmDU-5r2-19@gated-at.bofh.it> <rKnJE-62T-15@gated-at.bofh.it>
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On Wed, Jun 15, 2016 at 11:27:24AM -0700, Davidlohr Bueso wrote:
> On Wed, 15 Jun 2016, Peter Zijlstra wrote:
> 
> >In any case, its fairly simple to cure, just add
> >smp_acquire__after_ctrl_dep() at the end. If we bail because
> >need_resched() we don't need the acquire I think.
> 
> I was just considering this for your smp_cond_acquire/smp_cond_load_acquire

Right, so that need_resched break makes that a bit awkward. Not to
mention the cpu_relaxed() vs cpu_relaxed_lowlatency() difference.

> rework, so yeah I guess an smp_acquire__after_ctrl_dep would be a nice
> compromise.
> 
> However, I was always under the impression that races with node->locked were
> rather harmless (as indicated in the mentioned commit) -- which is why ->locked
> are simple load/stores, with the exception of the unqueueing -- but yeah, that's
> not even paired.

Yeah, see a few patches further in this series, where he guards a
variables with the osq_lock.

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Thread

[RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier Waiman Long <Waiman.Long@hpe.com> - 2016-06-15 00:50 +0200
  Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Boqun Feng <boqun.feng@gmail.com> - 2016-06-15 10:10 +0200
    Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Peter Zijlstra <peterz@infradead.org> - 2016-06-15 19:20 +0200
    Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Boqun Feng <boqun.feng@gmail.com> - 2016-06-16 04:20 +0200
      Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Will Deacon <will.deacon@arm.com> - 2016-06-16 12:20 +0200
      Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Boqun Feng <boqun.feng@gmail.com> - 2016-06-17 02:50 +0200
        Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Will Deacon <will.deacon@arm.com> - 2016-06-17 17:50 +0200
          Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Boqun Feng <boqun.feng@gmail.com> - 2016-06-18 10:50 +0200
            Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Will Deacon <will.deacon@arm.com> - 2016-06-20 10:10 +0200
  Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-06-15 19:00 +0200
    Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Peter Zijlstra <peterz@infradead.org> - 2016-06-15 19:20 +0200
      Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-06-15 20:30 +0200
        Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Peter Zijlstra <peterz@infradead.org> - 2016-06-15 20:50 +0200
          Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-06-15 21:00 +0200
          Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-06-17 03:20 +0200
            Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-06-17 18:30 +0200
              Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-06-17 18:50 +0200
      Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper  acquire/release barrier Peter Zijlstra <peterz@infradead.org> - 2016-06-16 00:00 +0200

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