dual Xeon issue

Steven Timm timm at fnal.gov
Thu Jun 5 14:45:11 EDT 2003


I'm not sure if I can explain the problem or not, but a crucial
piece of information that anyone would need to know to explain
it is--do you have the hyper-threading enabled or not?
Up until now we have found that Linux tends to allocate two
processes to the extra logical cpu's supplied with hyperthreading
without much regard to whether they are different physical
cpu's or not.  This can slow performance down.. doubly so if
you are dependent on memory bandwidth.

Steve


------------------------------------------------------------------
Steven C. Timm (630) 840-8525  timm at fnal.gov  http://home.fnal.gov/~timm/
Fermilab Computing Division/Core Support Services Dept.
Assistant Group Leader, Scientific Computing Support Group
Lead of Computing Farms Team

On Thu, 5 Jun 2003 sfrolov at accufo.vwh.net wrote:

> Sorry for a noob-like question. We are in the process of buying a Xeon-based cluster for scientific computing (running MPI parallelized numerical models). We've benchmarked clasters offered by Microway and Aspen Systems and discovered that we are getting much better results using only one CPU per box (running the model on 6 boxes using one CPU in each box was about 50% faster than running it on 3 boxes using both CPUs). This was surprising to us since we've used to be limited by interprocessor communications, which should be a lot faster between CPUs in one box. Can anybody explain the reason for this and, more importantly, is there any way to improve this situation.
>
> Thanks,
>
> Sergei.
>
> P.S. Can anybody recommend the best performance/price ratio cluster?
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