[mpich-devel] call PMI before MPI_Init_thread?

[Balaji, Pavan]

Multiple PMI Inits are not allowed.  It might work in the current implementation within MPICH, but is not safe.

If you are looking for MPICH specific behavior, you can look for the PMI_ID and PMI_RANK environment variables instead to get your rank.

  — Pavan

On Apr 21, 2015, at 11:17 PM, Jeff Hammond <jeff.science at gmail.com<mailto:jeff.science at gmail.com>> wrote:

So MPICH doesn't fail when I try this on my Mac, but it would be good
to know if I have a reasonable expectation of doing this in general.

Thanks,

Jeff

jrhammon-mac01:ENDPOINTS jrhammon$ mpiexec -n 4 ./a.out
PMI says I am 2 of 4
PMI says I am 0 of 4
PMI says I am 1 of 4
PMI says I am 3 of 4
MPI says I am 0 of 4 (provided=1)
MPI says I am 2 of 4 (provided=1)
MPI says I am 3 of 4 (provided=3)
MPI says I am 1 of 4 (provided=3)

jrhammon-mac01:ENDPOINTS jrhammon$ cat pmi.c
#include <stdio.h>
#include <stdlib.h>

/*#include <pmi.h>*/
int PMI_Init( int *spawned );
int PMI_Finalize( void );
int PMI_Get_size( int *size );
int PMI_Get_rank( int *rank );

#include <mpi.h>

int main(int argc, char * argv[])
{
   int has_parent;
   PMI_Init(&has_parent);

   int rank, size;
   PMI_Get_size(&size);
   PMI_Get_rank(&rank);

   printf("PMI says I am %d of %d \n", rank, size);
   fflush(stdout);

   int requested = (rank%2==0) ? MPI_THREAD_FUNNELED : MPI_THREAD_MULTIPLE;
   int provided;
   MPI_Init_thread(&argc, &argv, requested, &provided);

   int wsize, wrank;
   MPI_Comm_size(MPI_COMM_WORLD, &wsize);
   MPI_Comm_rank(MPI_COMM_WORLD, &wrank);

   printf("MPI says I am %d of %d (provided=%d)\n", wrank, wsize, provided);
   fflush(stdout);

   MPI_Finalize();
   //PMI_Finalize(); /* required? */

   return 0;
}

On Tue, Apr 21, 2015 at 9:09 PM, Jeff Hammond <jeff.science at gmail.com<mailto:jeff.science at gmail.com>> wrote:
Is it valid in _MPICH_ to make calls to PMI before MPI is initialized?
I am interested in PMI_Init, PMI_Get_size and PMI_Get_rank.

The motivating use case is to initialize e.g. half my ranks with
MPI_THREAD_FUNNELED and the other half with MPI_THREAD_MULTIPLE but
not use MPMD launching.

I have two reasons for wanting to do it this way.  First, it is
otherwise unnecessary to use MPMD since I can branch at the top of my
code and meet the requirements of FUNNELED and MULTIPLE.  Second, I
might be interested in running my code on a supercomputer with an
MPICH-based MPI implementation that does not support MPMD launching in
an unrestricted manner.

If MPICH can handle this, then I will worry about whether or not the
aforementioned supercomputer can.  It is my assumption that, if MPICH
cannot handle this, then the MPICH derivative in question cannot
either.

Thanks,

Jeff

--
Jeff Hammond
jeff.science at gmail.com<mailto:jeff.science at gmail.com>
http://jeffhammond.github.io/



--
Jeff Hammond
jeff.science at gmail.com<mailto:jeff.science at gmail.com>
http://jeffhammond.github.io/
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