Author: Robert Hyatt
Date: 15:04:19 02/19/03
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On February 19, 2003 at 16:41:09, Steffen Basting wrote: >On February 19, 2003 at 16:18:54, Charles Worthington wrote: > >>On February 19, 2003 at 16:13:58, Steffen Basting wrote: >> >>>Hi! >>>No, I would say Martin is right. You can do that with rather practical numbers: >>> >>>One processor, ht disabled: 1.000 nps. >>>=> Two processors, ht disabled: 2.000 nps. >>> >>>One processor, ht enabled: 1160 nps (ht disabled + 16%). >>>=> Two processors, ht enabled: 2.320 nps. >>> >>>and 2.000 * 1.16 = 2.320, so your speed up is 16% for both cpus. >>> >>> >>>Regards, Steffen >> >> >>actally the speedup is doubled when you are dealing with dual processors. You >>are using reverse mathematics to arrive at an incorrect answer. I honestly think >>Dr. Hyatt knows his math. > >There's no doubt that Dr. Hyatt knows his math - I just cannot see the "bug" in >my example. If the speed-up increases in the way you describe (n proc * 16%), it >would mean that with 16 processors ht enabled you arrive at 256%. So you are >faster than > 32 processors with ht disabled. This doesn't seem to be correct... > >Regards, Steffen this is semantics. It depends on how you define "percent faster". IE if you take a one processor machine as the benchmark, SMT will make it 20-30% faster with Crafty. If you take the two processor machine as the benchmark, it will run 20-30% faster with SMT. But that is 20-30% faster than two processors without SMT. That is the only way I really calculate this... What does the extra SMT thread gain, and the answer is adding that extra thread makes that physical processor 20-30% faster than it was without it.
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