Groups > linux.kernel > #1219591

Re: futex atomic vs ordering constraints

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: futex atomic vs ordering constraints
Date	2015-09-05 20:00 +0200
Message-ID	<q5pUS-7AS-5@gated-at.bofh.it> (permalink)
References	(3 earlier) <q3Z6p-72W-11@gated-at.bofh.it> <q4fNV-5vS-27@gated-at.bofh.it> <q4iVs-1Ic-3@gated-at.bofh.it> <q4jHP-2S4-13@gated-at.bofh.it> <q4nBL-8s3-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, Sep 02, 2015 at 02:18:53PM -0700, Linus Torvalds wrote:
> So I think we could possibly relax the requirements (and document this
> very clearly) to say that the futex operation must be totally ordered
> wrt any other _user_space_ accesses by that thread. I suspect a lot of
> architectures can then say "we may be very weakly ordered, but kernel
> entry/exit implies enough synchronization that we do not need any
> futher memory barriers".

Right, so before sending this email I actually spoke to Ralf about this
option, and he said that this is not actually well defined for MIPS.

But we could certainly document it such and let archs for which this is
well documented (I would expect this to be most) choose that
implementation.


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Thread

futex atomic vs ordering constraints Peter Zijlstra <peterz@infradead.org> - 2015-08-26 20:20 +0200
  Re: futex atomic vs ordering constraints Davidlohr Bueso <dave@stgolabs.net> - 2015-08-29 03:40 +0200
    Re: futex atomic vs ordering constraints Peter Zijlstra <peterz@infradead.org> - 2015-09-01 18:40 +0200
  Re: futex atomic vs ordering constraints Will Deacon <will.deacon@arm.com> - 2015-09-01 18:40 +0200
    Re: futex atomic vs ordering constraints Peter Zijlstra <peterz@infradead.org> - 2015-09-01 18:50 +0200
      Re: futex atomic vs ordering constraints Will Deacon <will.deacon@arm.com> - 2015-09-01 18:50 +0200
      Re: futex atomic vs ordering constraints Thomas Gleixner <tglx@linutronix.de> - 2015-09-01 21:10 +0200
        Re: futex atomic vs ordering constraints Peter Zijlstra <peterz@infradead.org> - 2015-09-02 15:00 +0200
          Re: futex atomic vs ordering constraints Chris Metcalf <cmetcalf@ezchip.com> - 2015-09-02 18:20 +0200
            Re: futex atomic vs ordering constraints Peter Zijlstra <peterz@infradead.org> - 2015-09-02 19:10 +0200
              Re: futex atomic vs ordering constraints Chris Metcalf <cmetcalf@ezchip.com> - 2015-09-02 19:30 +0200
              Re: futex atomic vs ordering constraints Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-02 23:20 +0200
                Re: futex atomic vs ordering constraints Peter Zijlstra <peterz@infradead.org> - 2015-09-05 20:00 +0200
                Re: futex atomic vs ordering constraints Will Deacon <will.deacon@arm.com> - 2015-09-07 11:40 +0200

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