[GE users] Implications of Hyperthread enabled CPUs and jobs

Neil Baker neil.baker at crl.toshiba.co.uk
Thu Nov 27 09:27:44 GMT 2008



I've been reading up on Hyper-thread enabled CPUs and am wondering if it is
best to disable or enable Hyper-threading in the BIOS?


Most of our grid machines have 2x physical 3.0 GHz Pentium 4 CPUs with
Hyper-threading enabled.  We are running openSuse10.0 on them (BIGSMP 2.6
kernel) so they appear to be 4x logical processors.


If 2 jobs are assigned to run on the same machine, is the kernel or grid
engine smart enough to run them on two physically separate CPUs, or is there
a random chance that they may both run on the same physical CPU (i.e. the
main and hyper-threaded logical CPU on the same physical CPU) and therefore
leave the other physical CPU totally unused? 


I've read that hyper-threading only gives up to 30% more performance, so by
accidentally running 2 jobs on the same physical CPU it is going to
drastically slow these jobs down compared with running them on two separate
physical CPUs.






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