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Re: [RFC][PATCH v3]: documentation,atomic: Add new documents

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH v3]: documentation,atomic: Add new documents
Date 2017-07-31 11:10 +0200
Message-ID <u9eS6-4nS-11@gated-at.bofh.it> (permalink)
References (2 earlier) <tQxVg-5AV-19@gated-at.bofh.it> <tRbzj-5Kd-9@gated-at.bofh.it> <tRyYW-3ny-15@gated-at.bofh.it> <u7t8R-8gu-5@gated-at.bofh.it> <u7tVg-mT-9@gated-at.bofh.it>
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On Wed, Jul 26, 2017 at 08:47:50PM +0800, Boqun Feng wrote:

> > +
> > +Further, while something like:
> > +
> > +  smp_mb__before_atomic();
> > +  atomic_dec(&X);
> > +
> > +is a 'typical' RELEASE pattern, the barrier is strictly stronger than
> > +a RELEASE. Similarly for something like:
> > +
> 
> .. at here. Maybe you planned to put stronger ACQUIRE pattern?

Yes, although I struggled to find a sensible one. The problem is that
ACQUIRE is on loads and value returning atomics have an ACQUIRE variant,
so why would you ever want to use smp_mb__after_atomic() for this.


That is, the best I could come up with is something like:

	val = atomic_fetch_or_relaxed(1, &var);
	smp_mb__after_atomic();

But in that case we should've just written:

	val = atomic_fetch_or_acquire(1, &var);


Suggestions?

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Thread

[RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra <peterz@infradead.org> - 2017-07-26 14:00 +0200
  Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Boqun Feng <boqun.feng@gmail.com> - 2017-07-26 14:50 +0200
    Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra <peterz@infradead.org> - 2017-07-31 11:10 +0200
      Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Boqun Feng <boqun.feng@gmail.com> - 2017-07-31 13:10 +0200
        Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-31 19:50 +0200
          Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Boqun Feng <boqun.feng@gmail.com> - 2017-08-01 04:20 +0200
          Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra <peterz@infradead.org> - 2017-08-01 11:10 +0200
            Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Will Deacon <will.deacon@arm.com> - 2017-08-01 12:20 +0200
              Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra <peterz@infradead.org> - 2017-08-01 13:50 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Will Deacon <will.deacon@arm.com> - 2017-08-01 14:20 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra <peterz@infradead.org> - 2017-08-01 15:00 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-01 18:20 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra <peterz@infradead.org> - 2017-08-01 18:50 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Will Deacon <will.deacon@arm.com> - 2017-08-01 19:00 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-02 00:20 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Will Deacon <will.deacon@arm.com> - 2017-08-02 10:50 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-01 20:40 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Will Deacon <will.deacon@arm.com> - 2017-08-02 11:50 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-02 18:20 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Boqun Feng <boqun.feng@gmail.com> - 2017-08-03 16:10 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-03 17:00 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Will Deacon <will.deacon@arm.com> - 2017-08-03 18:20 +0200
                Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-03 19:10 +0200
            Re: [RFC][PATCH v3]: documentation,atomic: Add new documents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-01 15:40 +0200
  Re: [RFC][PATCH v3]: documentation,atomic: Add new documents Randy Dunlap <rdunlap@infradead.org> - 2017-07-26 18:30 +0200

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