[mpich-devel] call PMI before MPI_Init_thread?

[Jeff Hammond]

Why not implement the equivalent of the ref-counting init proposal or
at least the simple things that allows multiple inits but only one
finalize?  Is it that you don't see the effort being worthwhile or
because there is a principled reason (PMI semantics should match MPI)?

Given that e.g. PGAS runtimes may want to use PMI for bootstrapping (I
do this with DMAPP code on Cray, for example), it seems to benefit
user experience to support this behavior.

Thanks,

Jeff

On Fri, Apr 24, 2015 at 1:12 AM, Balaji, Pavan <balaji at anl.gov> wrote:
>
> 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> 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>
> 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
> http://jeffhammond.github.io/
>
>
>
>
> --
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
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-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/