HPC/Applications/impi

Introduction

Intel-MPI is based on MPICH2 and provides an MPICH2 runtime environment for precompiled binaries.

See also

• HPC/Carbon Cluster - Development tools#MPI

Process manager

Use the Hydra process manager (new since impi version 4.x). See sec. 2.4 Scalable Process Management System in the Reference Manual. To do so, simply use mpiexec.hydra instead of the customary mpirun or mpiexec calls:

 mpiexec.hydra \
	-machinefile  $PBS_NODEFILE \
	-np $(wc -l < $PBS_NODEFILE) \
	./a.out

With Hydra, you no longer need to set up and tear down the older and considerably less stable MPD manager.

IMPI vs. OpenMPI

Since the openmpi module is loaded by default, use the following instead of module load impi:

module switch openmpi impi

However, the modules can coexist at runtime if:

• impi is loaded first and is called using mpiexec.hydra.
• openmpi is loaded second and is called using mpirun.
• binaries using impi are statically linked, i.e.,

ldd binary-using-impi | grep libmpi.so || echo OK

prints "OK".

• you don't attempt to compile software using the convenience wrappers like mpicc, mpif90, etc. For these wrappers, the last module loaded will be active. It may be possible to use full paths like $IMPI_HOME/bin/mpif90, but this has not been tested fully.

Since openmpi is loaded by default, use the following sequence in ~/.bashrc:

module unload openmpi
module load impi
module load openmpi

Caveat

This replaces possibly specific existing openmpi versions by the default version, which may break packages depending on it.

Why not load both modules by default?

While many files in those distributions differ and thus could coexist, key scripts and libraries use the same name, in particular the following:

(cd $OMPI_HOME; ls -1 {bin,lib}/* ) > /tmp/ompi
(cd $IMPI_HOME; ls -1 {bin,lib}/* ) > /tmp/impi
comm -1 -2 /tmp/?mpi
rm /tmp/?mpi

bin/mpicc
bin/mpicxx
bin/mpiexec
bin/mpif77
bin/mpif90
bin/mpirun
lib/libmpi.so