In my code, I put all ranks > 0 in a MPI_Barrier while rank 0 does some processing. But while on the barrier, the processes are consuming 100% of the processor.
Below is a sample code. Rank zero consumes 0% while on scanf but all other ranks consume 100% while on the barrier.
#include <stdio.h>
#include <mpi.h>
int main(int argc, char **argv) {
int rank;
int dummy;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
printf("MPI rank %i reporting in.\n", rank);
if ( rank == 0 ) {
printf("waiting for input\n");
scanf("%i", &dummy);
printf("ok\n");
MPI_Barrier(MPI_COMM_WORLD);
} else {
MPI_Barrier(MPI_COMM_WORLD);
}
return 0;
}
