[Beowulf] [gorelsky at stanford.edu: CCL:dual-core Opteron275performance]

Mikhail Kuzminsky kus at free.net
Thu Jul 14 08:29:40 PDT 2005

In message from "Kozin, I \(Igor\)" <i.kozin at dl.ac.uk> (Thu, 14 Jul 
2005 11:25:12 +0100):
>> But now for 4cores/2CPUs per Opteron node to force the using of
>> only 2 cores (from 4), by 1 for each chip, we'll need to have
>> cpu affinity support in Linux.
>you can use "taskset" for that purpose. 
>For example, (perhaps not in the most elegant form)
>	mpiexec  -n 1 taskset -c 0 $code : -n 1 taskset -c 2 $code
>But I doubt you want to let the idle cores to do something else 
>in the mean time. However small you will generally see an increase 
>in performance if you use all the cores.

Thanks !
AFAIK, taskset isn't a part of numactl package. Sorry, where is 
possible to download taskset ?

What is about using of all the cores, you are, of course, in
general right ;-)
But there may be some cases where using of "pairs of cores" on Opteron
is bad under parallelization. For example, test178/RHF on the same
G03 w/Linda, gave more worse performance on 2 cores than for 1 core
(because of extra memory traffic).
And, again at least theoretically, I may "occupy" 2 (free) of total
4 cores in 2-chip server for example w/some independed cache-friendly 



>I. Kozin  (i.kozin at dl.ac.uk)
>CCLRC Daresbury Laboratory
>tel: 01925 603308
>Distributed Computing Forum
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