MPI

We don't really use MPI for any day-to-day tasks in the CSL, but it's important to know how it works to support some of the high-powered Senior Research projects going on The Cluster and Parallel Computing labs.

Example MPI Program

Copied from a tutorial somewhere.

// hello_mpi_world.c
#include <mpi.h>
#include <stdio.h>
int main(int argc, char** argv) {
// Initialize the MPI environment
MPI_Init(NULL, NULL);
// Get the number of processes
int world_size;
MPI_Comm_size(MPI_COMM_WORLD, &world_size);
// Get the rank of the process
int world_rank;
MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
// Get the name of the processor
char processor_name[MPI_MAX_PROCESSOR_NAME];
int name_len;
MPI_Get_processor_name(processor_name, &name_len);
// Print off a hello world message
printf("Hello world from processor %s, rank %d out of %d processors\n",
processor_name, world_rank, world_size);
// Finalize the MPI environment.
MPI_Finalize();
}

Then, compile with mpicc --std=c99 hello_mpi_world.c -o hello_mpi_world And run with Slurm using srun -N4 ./hello_mpi_world (Or locally using mpirun -n4 ./hello_mpi_world)

What MPI software we use

  • PMIX 2.2.2

  • OpenMPI 3.1.3

See the relevant Ansible plays in Cluster Administration for more details on how it is installed.