[MITgcm-support] building with MPI on a dual-core mac

[Klymak Jody]

Hi Brian,

This was how I started on the macs as well.  I moved to openMPI when I  
got a cluster because it supports Xgrid. You also don't need to start  
a daemon (mpd).   OpenMPI compiles w/o any issues (that I recall).

Anyway, I get gfortran from http://hpc.sourceforge.net/ and openMPI  
from http://OpenMPI.org.

Note that each of your cores can run two processes w/o any problem.   
With your imac you could run -np 4 (though you may not want to surf  
the web at the same time).

Any reason you have these commands in your optfile?

NOOPTFLAGS='-O2 -funroll-loops'
NOOPTFILES='gad_c4_adv_x.F gad_u3_adv_x.F'

I don't have them, and my jobs run fine.  However maybe I'm not  
optimizing correctly.

Cheers,  Jody



On 17-Jul-09, at 3:44 PM, Brian Rose wrote:

> Hello MITgcmers,
>
> This is not really a question, but I just wanted to report on my  
> recent experience with setting up MITgcm with MPI support on a new  
> Apple iMac with Intel Core 2 Duo processor.  Though it's a single  
> machine, I got interested in building the model with MPI to take  
> advantage of the dual core processor.  I didn't find much  
> information about this particular setup in the email archives, but I  
> successfully muddled through it on my own.  I imagine this  
> information is obvious to some of you, but it certainly wasn't to  
> me, so I figured it would be useful contribution to this list.
>
> My system:
> iMac w/ 2.66 GHz Intel Core 2 Duo
> OS X 10.5.7
> gfortran 4.4.0 (installed via fink)
> mpich2-1.1
>
> I found many ways to install MPI that *didn't* work, and one way  
> that *did* work.  There is a version of OpenMPI pre-installed with  
> OS X 10.5, but without a Fortran compiler so it's pretty much  
> useless for our purposes.
>
> What worked for me was to download the source code for the latest  
> stable release of MPICH2, and build it with gfortran using the same  
> compiler flags as I need to compile MITgcm.  Specifically, I ran the  
> mpich2 configure script with the following flags
> F90=gfortran F77=gfortran F90FLAGS='-fsecond-underscore' FFLAGS='- 
> fsecond-underscore'
> and then proceeded to build mpich2 following the stock instructions  
> that came with the distribution.
> (without the '-fsecond-underscore' flags, I got linker errors when  
> building MITgcm)
>
> MITgcm now compiles and runs without complaint, using the optfile  
> attached below.
>
> To run the model on two cores, I did the following:
> - edit SIZE.h with nPx = 2
> - follow the usual build sequence, using the '-mpi' option for  
> genmake2
> - before running the model, launch the 'mpd' daemon (that was  
> installed along with mpich2) by typing 'mpd &' on the command line
> - to run the model:  'mpiexec -n 2 ./mitgcmuv'
>
> And it works!  The limited testing I have done shows a speed-up  
> factor of about 1.6 over a single-processor build.
>
> Hope this information, and/or the optfile below, is useful to  
> somebody.
>
> Cheers
> Brian
>
> <darwin_ia32_gfortran+mpi>
>
>
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> Brian Rose
> Ph.D. Candidate, Climate Physics and Chemistry
> Department of Earth, Atmospheric and Planetary Sciences
> Massachusetts Institute of Technology
> office: 54-1419          phone: 617-253-9345
> email:  brose at mit.edu
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
>
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