Change arguments of called programs (SMPI entry points)?

[mpoquet]

The way SMPI programs are called seems strange to me in current SMPI.

I can implement the following, which might be saner for users.

• set the executed program as argv[0]
• remove the rank from the arguments

What do you think?

Example

Here is a tiny MPI program.

#include <mpi.h>
#include <stdio.h>

int main(int argc, char** argv)
{
    MPI_Init(&argc, &argv);

    int rank, size;
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    printf("rank=%d, size=%d, args=['%s'", rank, size, argv[0]);
    for (int i = 1; i < argc; i++)
        printf(", '%s'", argv[i]);
    printf("]\n");

    MPI_Finalize();
    return 0;
}

Execution with usual MPI implementation

With OpenMPI, running

mpicc hello.c -o hello
mpirun -np 2 ./hello mpi world

outputs

rank=0, size=2, args=['./hello', 'mpi', 'world']
rank=1, size=2, args=['./hello', 'mpi', 'world']

Execution with SMPI

With SimGrid (81e177c), running

smpicc hello.c -o hello
smpirun -platform ${SG_DIR}/examples/platforms/small_platform.xml \
        -hostfile ${SG_DIR}/examples/smpi/hostfile \
        --log=xbt_cfg.thresh:warning --log=smpi_kernel.thresh:warning \
        -np 2 ./hello mpi world

outputs

rank=0, size=2, args=['0', 'mpi', 'world']
rank=1, size=2, args=['1', 'mpi', 'world']

[mpoquet]

After some tests, I think I'll rather keep rank and add instance_id in the entry points' arguments, and remove those additional arguments when leaving PMPI_Init (and maybe do something else for FORTRAN, as the way args are set for FORTRAN is already specialized in current code base).

This would allow the smpi-msg-masterslave example to work the same way that it is doing now (actor initialization in PMPI_Init), while wiping out these internal arguments from argc/argv once user apps have called MPI_Init.

[mpoquet]

Or change smpirun so it uses actor properties instead of arguments!

[agiersch]

Tested with the current version, and got the expected result:

rank=1, size=2, args=['./hello', 'mpi', 'world']
rank=0, size=2, args=['./hello', 'mpi', 'world']

Closing.