Author: Tom Kerrigan
Date: 12:50:22 04/14/03
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On April 13, 2003 at 11:21:51, Robert Hyatt wrote: >On April 13, 2003 at 02:37:57, Tom Kerrigan wrote: > >>On April 13, 2003 at 01:04:52, Robert Hyatt wrote: >> >>>It _is_ pinned on SMT. The two logical processors are producing wildly >>>imbalanced results when using threads, vs using two separate processes. It >>>would appear to be cache-related... >> >>This is some sort of joke, right? You and Vincent see the same behavior, you >>have SMT and Vincent doesn't, and somehow the problem is with SMT? >. > > >The _variability_ is with SMT. What are you talking about? I reported _two_ >issues. > >1. My dual xeon runs two copies of crafty about 2x as fast as if they were >run one after the other. So does my quad 700. > >2. My dual xeon runs one copy, two threads, at about 1.5X the speed that it >should. > >That is a problem. > >The second issue is that my dual xeon does _not_ run threaded crafty in a >balanced way on two logical processors. For two independent copies, it >varies from 50-50 to 45-55. Not unreasonable. But for the single threaded >copy, it varies all the way to 70-30. _that_ is an SMT issue. Probably, as >I mentioned, caused by some unknown L2 cache issue. But it _is_ a problem >with SMT if you want to assume that normally it is about 50-50 roughly, for >_regular_ applications. > >shared memory, locks, etc are causing something strange to happen. It looks like you're having enough problems and unexplained behavior already that it's hard to trust any sort of numbers you post. But still, if the widest disparity you measured was 70-30, that seems like enough to dispel your notion that one thread always gets priority over the other. -Tom
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