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Subject: Re: wmb vs mmiowb
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
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> Of course, the normal memory barrier would usually be a "spin_unlock()" or 
> something like that, not a "wmb()". In fact, I don't think the powerpc 
> implementation (as an example of this) will actually synchronize with 
> anything *but* a spin_unlock().

We are even more sneaky in the sense that we set a per-cpu flag on any
MMIO write and do the sync automatically in spin_unlock() :-)

Ben.