| Subject | Re: perf events ring buffer memory barrier on powerpc | From | Victor Kaplansky <> | Date | Wed, 30 Oct 2013 16:52:05 +0200 |
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Peter Zijlstra <peterz@infradead.org> wrote on 10/30/2013 01:25:26 PM:
> Also, I'm not entirely sure on C, that too seems like a dependency, we > simply cannot read the buffer @tail before we've read the tail itself, > now can we? Similarly we cannot compare tail to head without having the > head read completed.
No, this one we cannot omit, because our problem on consumer side is not with @tail, which is written exclusively by consumer, but with @head.
BTW, it is why you also don't need ACCESS_ONCE() around @tail, but only around @head read.
-- Victor
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