[MITgcm-support] mpi with 4 processors

[Angela Marie Zalucha]

I'll be more explicit about what I tried in 3D:

sNx =  16,
sNy =  32,
nSx =   3,
nSy =   1,
nPx =   4,
nPy =   1,


On Mon, 1 Nov 2010, Holly Dail wrote:

> Hi Angela -
>
> Your problem, especially the 2-D one, may simply be too small to benefit 
> from more than 2 processors (i.e. the added communication costs of using 
> 4 isn't compensating for the faster computation).  Have you found that 
> the nSx=6 is helpful for your machine?  I'm currently running on 24 
> processors (Pleiades) with the following SIZE.h:
>
>     &           sNx = 20,
>     &           sNy = 27,
>     &           OLx =   3,
>     &           OLy =   3,
>     &           nSx =   1,
>     &           nSy =   1,
>     &           nPx =   6,
>     &           nPy =   4,
>     &           Nx  = sNx*nSx*nPx,
>     &           Ny  = sNy*nSy*nPy,
>     &           Nr  =  23)
>
> Holly
>
> On Nov 1, 2010, at Nov 1 , 1:44 PM, Angela Marie Zalucha wrote:
>
>> 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
>>
>> _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
>> 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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>> MITgcm-support at mitgcm.org
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>
>
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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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