Douglas Guptill wrote: > On Tue, May 04, 2010 at 05:34:40PM -0600, Ralph Castain wrote: >> On May 4, 2010, at 4:51 PM, Gus Correa wrote: >> >>> Hi Ralph >>> >>> Ralph Castain wrote: >>>> One possibility is that the sm btl might not like that you have >>>> hyperthreading enabled. >>> I remember that hyperthreading was discussed months ago, >>> in the previous incarnation of this problem/thread/discussion on "Nehalem >>> vs. Open MPI". >>> (It sounds like one of those supreme court cases ... ) >>> >>> I don't really administer that machine, >>> or any machine with hyperthreading, >>> so I am not much familiar to the HT nitty-gritty. >>> How do I turn off hyperthreading? >>> Is it a BIOS or a Linux thing? >>> I may try that. >> I believe it can be turned off via an admin-level cmd, but I'm not certain >> about it > > The challenge was too great to resist, so I yielded, and rebooted my > Nehalem (Core i7 920 @ 2.67 GHz) to confirm my thoughts on the issue. > > Entering the BIOS setup by pressing "DEL", and "right-arrowing" over > to "Advanced", then "down arrow" to "CPU configuration", I found a > setting called "Intel (R) HT Technology". The help dialogue says > "When Disabled only one thread per core is enabled". > > Mine is "Enabled", and I see 8 cpus. The Core i7, to my > understanding, is a 4 core chip.
That's correct, HyperThreading makes it look like there are twice as many cores as there physically are. So an n-core system will look like it has 2n cores to the OS when HT is enabled. -- Prentice
