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Preventing overly-optimistic spinningPreventing overly-optimistic spinningPosted Aug 26, 2010 16:10 UTC (Thu) by jzbiciak (✭ supporter ✭, #5246)In reply to: Preventing overly-optimistic spinning by PaulMcKenney Parent article: Preventing overly-optimistic spinning
I guess it would depend on the cache protocol too, wouldn't it?
In a MESI, you would end up bouncing lines (S => M transition on the first writer, S => I on the others, followed by M => S and I => S). An ESI system (write through caches w/ no notion of "modified"), you'd get something similar.
In a MOESI such as Athlon's, I believe you minimize the cost. The first writer does an S => O and broadcasts the write to everyone else that's in S.
From that, I'd say it's rather important to measure on multiple architectures, since the tradeoffs will vary.
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Preventing overly-optimistic spinning Posted Aug 26, 2010 16:25 UTC (Thu) by PaulMcKenney (subscriber, #9624) [Link]
I agree with your MESI assessment, but would want to see test results for the MOESI case -- there would be added traffic from the broadcasts. Which is all to say that I very much agree with you about the importance of testing on multiple architectures!
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