Messages in this thread | | | Date | Mon, 13 Jul 2015 15:24:18 +0100 | From | Will Deacon <> | Subject | Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() |
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On Mon, Jul 13, 2015 at 02:09:50PM +0100, Peter Hurley wrote: > On 07/13/2015 08:15 AM, Will Deacon wrote: > > smp_mb__after_unlock_lock is used to promote an UNLOCK + LOCK sequence > > into a full memory barrier. > > > > However: > > > > - This ordering guarantee is already provided without the barrier on > > all architectures apart from PowerPC > > > > - The barrier only applies to UNLOCK + LOCK, not general > > RELEASE + ACQUIRE operations > > I'm unclear what you mean here: do you mean > A) a memory barrier is not required between RELEASE M + ACQUIRE N when you > want to maintain distinct order between those operations on all arches > (with the possible exception of PowerPC), or, > B) no one is using smp_mb__after_unlock_lock() in that way right now.
My understanding is (B), but Peter and I don't seem to agree yet! I'll tighten up the text once we reach a conclusion.
Will
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