[MITgcm-support] mpi with 4 processors

[Angela Marie Zalucha]

Hi,

I am trying to figure out how to use the MIT GCM with multiple processors. 
I found the examples for how to modify SIZE.h for 2 processors.  In 2D I 
use:

  sNx =   1,
  sNy =  32,
  nSx =   1,
  nSy =   1,
  nPx =   1,
  nPy =   2,

In 3D I use:

  sNx =  16,
  sNy =  32,
  nSx =   6,
  nSy =   1,
  nPx =   2,
  nPy =   1,

Indeed, there is a significant improvement in speed over 1 processor.  I 
have up to 4 processors available to me, but the configurations I have 
tried with 4 processors don't run any faster than with 2.  Is there any 
optimum configuration I can use with 4 processors?  Or 3 processors if 4 
is not possible?

It might be that I'm not understanding how to scale things for more 
processors, so any example with n > 2 would be helpful.

I use gfortran for the compiler and mpich2 for mpi.  I am running on 
computers at Southwest Research Institute in Boulder, CO.  I am using 30 
vertical levels.

   Angela

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Angela Zalucha, Ph.D.
Postdoctoral Associate
Department of Earth, Atmospheric,
   and Planetary Sciences
Massachusetts Institute of Technology

Office located at Southwest Research Institute
1050 Walnut Street, Suite 300
Boulder, CO 80302
(720) 208-7211


http://web.mit.edu/azalucha/www/index.html
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