OpenMPI

The Open MPI Project is an open source MPI-2 implementation that is developed and maintained by a consortium of academic, research, and industry partners. Open MPI is therefore able to combine the expertise, technologies, and resources from all across the High Performance Computing community in order to build the best MPI library available. Open MPI offers advantages for system and software vendors, application developers and computer science researchers.

OpenMPI installations on LRZ systems

On LRZ HPC Systems, OpenMPI is used for research and experimental purposes. This means that while LRZ support staff will do its best to help you with problems, we do not have any commercial-level support and hence cannot give any functional or reliability guarantees for using this software. Also, programs built with OpenMPI will often not scale as well as the proprietary MPI implementations on the high-end systems.

The following command will list available OpenMPI modules on the LRZ HPC systems:

module avail openmpi

Please consider that this command lists modules from the currently loaded software stack. Please learn more about software stacks here.

The module name usually has the following structure: openmpi/version-compiler with name and version of the supported compiler. Examples: openmpi/4.1.5-gcc11, openmpi/4.1.5-intel23

In order to access the OpenMPI installation, the appropriate environment module must be loaded after unloading the default MPI environment, and after loading a suitable compiler. For example, the command sequence

module unload intel-mpi

module load openmpi/4.1.5-intel23

or

module switch intel-mpi openmpi/4.1.5-intel23

can be used, to select one of the OpenMPI installations from the table above. To compile and link the program, the mpicc / mpiCC / mpifort commands are available.

Usage of OpenMPI is typical for the LRZ MPI installations with respect to compiler wrappers and startup commands; special variants are described below.

The OpenMPI builds are all done with MPI_THREAD_MULTIPLE enabled.

Specific OpenMPI usage scenarios

Running OpenMPI programs on SuperMUC-NG

Please consult the Job Processing with SLURM on the SuperMUC-NG page; starting out from a job script for Intel MPI, it should be sufficient to make the following change:

  1. Switch modules

    module switch intel-mpi openmpi/4.0.4-intel19


  2. Start the program with the srun . You can use mpiexec if you deactivate also ear with the following sbatch option:
#SBATCH --ear=off 

Running OpenMPI programs on the Linux Cluster

Please consult the Running parallel jobs on the Linux Cluster page; starting out from a job script from the "Distributed-memory jobs" section, it should be sufficient to replace loading Intel MPI (called "intel-mpi" or "intel-toolkit") module by OpenMPI module, e.g.:

  1. Switch Intel and OpenMPI modules:

    module switch intel-toolkit openmpi/4.0.4-intel19

  2. Start the program with the srun or mpiexec command analogous to the command line specified for SuperMUC-NG above.

Documentation

Documentation, as well as Frequently Asked Questions pages, are available on the OpenMPI website.

Also, man pages are available for the various OpenMPI commands, especially mpi(3) and srun(1).