Author: Robert Hyatt
Date: 10:46:26 05/21/03
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On May 20, 2003 at 13:52:01, Tom Kerrigan wrote: >On May 20, 2003 at 00:26:49, Robert Hyatt wrote: > >>Actually it _does_ surprise me. The basic idea is that HT provides improved >>resource utilization within the CPU. IE would you prefer to have a dual 600mhz >>or a single 1000mhz machine? I'd generally prefer the dual 600, although for > >You're oversimplifying HT. When HT is running two threads, each thread only gets >half of the core's resources. So instead of your 1GHz vs. dual 600MHz situation, >what you have is more like a 1GHz Pentium 4 vs. a dual 1GHz Pentium. The dual >will usually be faster, but in many cases it will be slower, sometimes by a wide >margin. Not quite. Otherwise how do you explain my NPS _increase_ when using a second thread on a single physical cpu? The issue is that now things can be overlapped and more of the CPU core gets utilized for a greater percent of the total run-time... If it were just 50-50 then there would be _zero_ improvement for perfect algorithms, and a negative improvement for any algorithm with any overhead whatsoever... And the 50-50 doesn't even hold true for all cases, as my test results have shown, even though I have yet to find any reason for what is going on... > >>Could it be slower in some? Of course. But then the algorithm(s) in question >>need work, obviously... > >No. See above. Ditto. a 1ghz cpu is not the same as two 500's, in the context of SMT. Otherwise it would _always_ be senseless to use two 500's... The 1000 would _always_ be faster. But it isn't, so this is moot... > >-Tom
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