Running MPI jobs¶
There are several available MPI implementations on our group cluster:
OpenMPI provided by the
openHPC
module, e.g.module load openmpi3/3.1.4
OpenMPI provided by the
nvHPC
module, e.g.module load nvhpc/21.3
OpenMPI compiled for the
intel
module, e.g.module load openmpi/3.1.4/intel
Intel MPI provided by the
intel
module, e.g.module load mpi/latest
There are several ways of launching an MPI application within a SLURM
allocation, e.g. srun
, mpirun
, mpiexec
and mpiexec.hydra
.
Unfortunately, the best way to launch your program depends on the MPI
implementation (and possibly your application), and choosing the wrong command
can severly affect the efficiency of your parallel run. Our recommendation is
the following:
Intel MPI¶
With Intel MPI, we have found that mpirun
can incorrectly distribute the
MPI ranks among the allocated nodes. We thus recommend using srun
:
$ srun --mpi=pmi2 ./my_application
OpenMPI¶
With OpenMPI, mpirun
seems to be working correctly. Also, it seems that
srun
fails to launch your application in parallel, so here we recommend
using mpirun
:
$ mpirun ./my_application