[Beowulf] Re: Opteron 275 performance

[Steve Cousins]

On Thu, 14 Jul 2005 11:25:12 +0100 Igor Kozin wrote:

>  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.
> 
> Mikhail,
> 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.

We are considering getting a Dual Dual-Core Opteron system vs. two Dual
Opteron systems.  We like the ability to use all four cores on one model
but a lot of what we'll do is have two models running at the same time,
each using two cores.  

We are worried that running two models on one system with four cores (each
model using two cores) will not work as well as using two systems, each
with two cores/cpu's.  Is this what you were refering to (Igor) when you
wrote:

> But I doubt you want to let the idle cores to do something else
> in the mean time. 

We have an 8 CPU SGI Origin 3200 that has no problem doing this sort of
thing.  I'm just curious what the implications are of doing this with the
Dual Core Opteron cpu's.  

Thanks,

Steve 
______________________________________________________________________
 Steve Cousins, Ocean Modeling Group    Email: cousins at umit.maine.edu
 Marine Sciences, 208 Libby Hall        http://rocky.umeoce.maine.edu
 Univ. of Maine, Orono, ME 04469        Phone: (207) 581-4302