Messages in this thread | | | Date | Wed, 16 Sep 2015 12:43:14 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] barriers: introduce smp_mb__release_acquire and update documentation |
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On Wed, Sep 16, 2015 at 11:29:08AM +0100, Will Deacon wrote: > > Indeed, that is a hole in the definition, that I think we should close.
> I'm struggling to understand the hole, but here's my intuition. If an > ACQUIRE on CPUx reads from a RELEASE by CPUy, then I'd expect CPUx to > observe all memory accessed performed by CPUy prior to the RELEASE > before it observes the RELEASE itself, regardless of this new barrier. > I think this matches what we currently have in memory-barriers.txt (i.e. > acquire/release are neither transitive or multi-copy atomic).
Ah agreed. I seem to have gotten my brain in a tangle.
Basically where a program order release+acquire relies on an address dependency, a cross cpu release+acquire relies on causality. If we observe the release, we must also observe everything prior to it etc.
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