On Friday 19 November 2010 16:51:00 Tom Lane wrote: > Markus Wanner <mar...@bluegap.ch> writes: > > Well, that certainly doesn't apply to full fences, that are not specific > > to a particular piece of memory. I'm thinking of 'mfence' on x86_64 or > > 'mf' on ia64. > Hm, what do those do exactly? We've never had any such thing in the > Intel-ish spinlock asm, but if out-of-order writes are possible I should > think we'd need 'em. Or does "lock xchgb" imply an mfence? Out of order writes are definitely possible if you consider multiple processors. Locked statments like 'lock xaddl;' guarantee that the specific operands (or their cachelines) are visible on all processors and are done atomically - but its not influencing the whole cache like mfence would.
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