On Fri, Aug 7, 2009 at 7:58 PM, Gus Correa<g...@ldeo.columbia.edu> wrote: > Some people are reporting good results when using the > Nehalem hypethreading feature (activated on the BIOS). > When the code permits, this virtually doubles the number > of cores on Nehalems. > That feature works very well on IBM PPC-6 processors > (IBM calls it "simultaneous multi-threading" SMT, IIRR), > and scales by a factor of >1.5, at least with the atmospheric > model I tried.
Thanks for all the useful comments, Gus! Hyperthreading is confusing the hell out of me. I expected to see 8 cores in cat /proc/cpuinfo Now I see 16. (This means I must have left hyperthreading on I guess; I ought to go to the server room; reboot and check the BIOS) This is confusing my benchmarking too. Let's say I ran an MPI job with -np 4. If there was no other job on this machine would hyperthreading bring the other CPUs into play as well? The reason I ask is this: I have noticed that a single 4 core job is slower than two 4 core jobs run simultanously. This seems puzzling to me. -- Rahul _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
