Author: Robert Hyatt
Date: 19:58:36 04/14/04
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On April 14, 2004 at 22:51:45, Slater Wold wrote: >On April 14, 2004 at 22:49:39, Robert Hyatt wrote: > >>I just finished some HT on / HT off tests to see how things have changed in >>Crafty since some of the recent NUMA-related memory changes that were made. >> >>Point 1. HT now speeds Crafty up between 5 and 10% max. A year ago this was >>30%. What did I learn? Nothing new. Memory waits benefit HT. Eugene and I >>worked on removing several shared memory interactions which led to better cache >>utilization, less cache invalidates (very slow) and improved performance a good >>bit. But at the same time, now HT doesn't have the excessive memory waits it >>had before and so the speedup is not as good. >> >>Point 2. HT now actually slows things down due to SMP overhead. IE I lose 30% >>per CPU, roughly, due to SMP overhead. HT now only gives 5-10% back. This is a >>net loss. I am now running my dual with HT disabled... >> >>More as I get more data... Here is two data points however: >> >>pos1. cpus=2 (no HT) NPS = 2.07M time=18.13 >> cpus=4 NPS = 2.08M time=28.76 >> >>pos2. cpus=2 NPS = 1.87M time=58.48 >> cpus=4 NPS = 2.01M time=66.00 >> >>First pos HT helps almost none in NPS, costs 10 seconds in search overhead. >>Ugly. Position 2 gives about 5% more nps, but again the SMP overhead washes >>that out and there is a net loss. I should run the speedup tests several times, >>but the NPS numbers don't change much, and the speedup could change. But this >>offers enough.. > >What were the positions? Kopec 22 and 23. Had a script to run them. I actually ran all 24, but a glitch had something else running for most of the second run so the last 3 were all that was really usable...
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