Introduction to MPI Programming

The goal of this section is to introduce you to MPI programming using OpenMPI.

Hands-on

Remember to setup the environment as described in the Environment section:

1. ssh passwordless
2. shared working directory (you have to do nothing, is already there)
3. setup the correct export for PATH and LD_LIBRARY_PATH in the .bashrc

Check that your environment is correctly configured to compile MPI code by running:

$ mpic++ --version
g++ (GCC) 11.5.0 20240719 (Red Hat 11.5.0-11)
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compile and run the MPI executable:

$ cd sesame26/hands-on/mpi
$ mpic++ -o MPI_Hello.out MPI_Hello.cpp
$ mpirun  -n 2 MPI_Hello.out
$ mpirun -hostfile machinefile.txt -n 2 MPI_Hello.out

You can now go and try with the other exercises avalble on the sesame/hands-on/mpi directory (see the slides for more details):

1. The MPI PingPong

   $ mpic++ -o PingPong.out PingPong.cpp
   $ mpirun -n 2 -hostfile machinefile.txt PingPong.out
   

2. The Non-Blocking MPI PingPong

   $ mpic++ -o NoBloc_PingPong.out NoBloc_PingPong.cpp
   $ mpirun -n 2 -hostfile machinefile.txt NoBloc_PingPong.out
   

3. The trivial BandWidth measure

   $ mpic++ -o BandWidth.out BandWidth.cpp
   $ mpirun -n 2 -hostfile machinefile.txt BandWidth.out  # this will use infiniband
   $ mpirun -n 2 -hostfile machinefile.txt --mca btl tcp,self,vader --mca pml ob1 --mca btl_tcp_if_include eth0 BandWidth.out    #this will use ethernet
   

4. The MPI Pi Computation

   $ mpic++ -o MPI_Pi.out MPI_Pi.cpp
   $ mpirun -n 2 MPI_Pi.out    # try to increase the number of processes
   

5. The Trivial MPI N-Body Simulation

   $ mpic++ -o MPI_NBody.out MPI_NBody.cpp
   $ mpirun -n 2 MPI_NBody.out    # try to increase the number of processes