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Subject: Re: [OMPI users] Redefine proc in cartesian topologies
From: Claudio Pastorino (claudio.pastorino_at_[hidden])
Date: 2012-03-01 14:34:36


Hi, thanks for the answer.
 You are right is not the rank what matters but how do I arrange
the physical procs in the cartesian topology. I don't care about the label.
So, how do I achieve that?

Regards,
Claudio

2012/3/1, Ralph Castain <rhc_at_[hidden]>:
> Is it really the rank that matters, or where the rank is located? For
> example, you could leave the ranks as assigned by the cartesian topology,
> but then map them so that ranks 0 and 2 share a node, 1 and 3 share a node,
> etc.
>
> Is that what you are trying to achieve?
>
>
> On Mar 1, 2012, at 11:57 AM, Claudio Pastorino wrote:
>
>> Dear all,
>> I apologize in advance if this is not the right list to post this. I
>> am a newcomer and please let me know if I should be sending this to
>> another list.
>>
>> I program MPI trying to do HPC parallel programs. In particular I
>> wrote a parallel code
>> for molecular dynamics simulations. The program splits the work in a
>> matrix of procs and
>> I send messages along rows and columns in an equal basis. I learnt
>> that the typical
>> arrangement of cartesian topology is not usually the best option,
>> because in a matrix, let's say of 4x4 procs with quad procs, the
>> procs are arranged so that
>> through columns one stays inside the same quad proc and through rows
>> you are always going out to the network. This means procs are
>> arranged as one quad per row.
>>
>> I try to explain this for a 2x2 case. The cartesian topology does this
>> assignment, typically:
>> cartesian mpi_comm_world
>> 0,0 --> 0
>> 0,1 --> 1
>> 1,0 --> 2
>> 1,1 --> 3
>> The question is, how do I get a "user defined" assignment such as:
>> 0,0 --> 0
>> 0,1 --> 2
>> 1,0 --> 1
>> 1,1 --> 3
>>
>> ?
>>
>> Thanks in advance and I hope to have made this more or less
>> understandable.
>> Claudio
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>
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