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MathGroup Archive 2007

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Re: Mathematica, Quad Core, Linux

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73236] Re: Mathematica, Quad Core, Linux
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 8 Feb 2007 03:41:52 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <eqc7tb$snu$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

when you are using Mathematica, the kernel will use a single processor
core 99 % of the time -- but this depend on the kind of computation
you are doing. Only a few numerical functions use the other cores.

These few numerical functions are parallelized with OpenMP and *you* 
have to tell OpenMP how many processor you wish to use with the
OMP_NUM_THREADS environment variable. Thats because you may have
a single processor, that allows HyperThreading and you can run two
threads on even one processor, or you have a Quad core machine but you
wish to reserve one processor for a web-server or something else you 
have to set the OMP_NUM_THREADS variable to a value less than 4, but if
you Quad core processor allow HyperThreading, you can set the number
of threads to a higher value.

It is very unlikely that a general propose program like Mathematica
(that wait the most time for Shift-Enter) can be parallelized in
a way that it run all processor with full load.

Regards
   Jens


lkhagvad wrote:
> Hi:
> 
> I would like to ask for your help from those who actually use quad core machines with Mathematica.
> 
> 1. More specifically, I would like to know what experiences other academic users have on running Mathematica on Quad Core Linux. And also, is it difficult to set up and get it running?  At this stage any comment is valuable from those who have it all working nicely?
> 
> 2. I got the following negative general comment on running multi-processor for parallel computing. "The parallelization is done at the beginning of the run. So,
> if you tell the program (or the program finds) there are 4 cores available at the start of the program, it grabs them and assumes they will be available exclusively to the program. If a second user logs in and tries to run something, processing speed will be terrible." Is this also the case with the Mathematica Quad Core combination?
> 
> Thank you very much for all your help.
> 
> Damba.
> 


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