Author: Robert Hyatt
Date: 19:20:57 05/21/03
Go up one level in this thread
On May 21, 2003 at 15:48:46, Tom Kerrigan wrote: >On May 21, 2003 at 13:46:26, Robert Hyatt wrote: > >>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... > >Think a little bit before posting, Bob. I said that the chip's execution >resources were evenly split, I didn't say that the chip's performance is evently >split. That's just stupid. You have to figure in how those execution resources >are utilized and understand that adding more of these resources gives you >diminishing returns. > >-Tom You shold follow your own advice. If resources are split "50-50" then how can _my_ program produce a 70-30 split on occasion? It simply is _not_ possible. There is more to this than a simple explanation offers...
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