Author: Robert Hyatt
Date: 22:04:52 04/12/03
Go up one level in this thread
On April 12, 2003 at 23:32:22, Tom Kerrigan wrote: >On April 12, 2003 at 01:24:33, Robert Hyatt wrote: > >>I ran the test Tom suggested. Two different ways. >> >>First, four different threads. Results were a pretty even balance, varying >>from 45-55, to 49-51 depending on the run. Not bad. >> >>Then two programs using two threads each, using a patched kernel that let me >>lock a thread to a processor. Result was wildly varying. with a best of 60-40 >>and a worst of 75-25. Why that is I have absolutely no idea. But even more >>interesting is that the two threads seem to "lose" time for reasons unknown at >>the moment. IE total time increases by about 30-50% which I don't understand at >>all. This still points to some odd cache issue I believe, and it seems to >>really influence SMT in a strange way... >> >>I'm trying to understand the two-thread results as they are probably related to >>the problem Vincent pointed out last week (NPS about 1.5X a single using a dual >>with no SMT at all.) Something is definitely fishy when I use threads. And >>the balance between CPUS is nowhere near 50-50 for some reason... > >Hope you're not trying to pin that on SMT. > >-Tom 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...
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