Author: Robert Hyatt
Date: 14:54:14 04/14/03
Go up one level in this thread
On April 14, 2003 at 15:50:22, Tom Kerrigan wrote: >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 How? 70-30 is > 2:1. Something is going on.
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