How to compile a Fortran code for profiling with gprof in OpenMPI?

I am able to compile my Openmpi code using gfortran compiler. The compile syntax I give is :

mpif90 -o mycode.exe mycode.f90

mpirun -np 4 ./mycode.exe

It works. And now I want to profile my code using Gprof. I know I should add the -pg flag, but if I put it after mpif90 it crashed. Where should I put the flag?

You can give this a try, see how it yields. Assume you are using openmpi. Create the following as script named mywrapper.sh

#!/bin/bash
prefix="gmon_${OMPI_COMM_WORLD_RANK}.out"
GMON_OUT_PREFIX=$prefix $*

And run your code with

mpif90 -o mycode.exe -pg mycode.f90
mpirun -np 4 mywrapper.sh ./mycode.exe

Test code of profiling MPI code (I am using C, but FORTRAN should work without difference) :

//file x.c
#include <mpi.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
    int rank=9;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    printf("Hello from rank=%d!\n", rank);
    MPI_Finalize();
    return 0;
}

Command to compile and run the test

#!/bin/bash
mpicc -pg x.c
mpirun --hostfile hostfile mywrapper.sh ./a.out

For simplicity test, hostfile use local host only. The command output:

Hello from rank=1!
Hello from rank=2!
Hello from rank=0!

Then you get those gprof file, if cannot, must be mpi configuration issue.

.
├── a.out
├── gmon_0.out.2690
├── gmon_1.out.2692
├── gmon_2.out.2693