Code execution

When using OpenMPI, binding is controlled using the –-bind-to parameter. To bind processes to cores, use --bind-to core. Possible other values can be found in the man page.

mpirun --bind-to core ./yourprogram

Our hardware supports hyperthreading, allowing you start 192 processes on Cascade Lake machines (*96 partitions) and 80 on Skylake machines.

If no specific requests regarding the number of tasks has been done, mpirun defaults to hyperthreading and starts cores*2 processes. If a number of tasks has been specified (either with -n or --tasks-per-node), mpirun  honors this. For example:

#!/bin/bash
#SBATCH -N 4

module load gcc/9.2.0 openmpi/gcc.9/3.1.5

cpus_per_node=${SLURM_JOB_CPUS_PER_NODE%\(*}
export OMP_NUM_THREADS=$(($cpus_per_node*$SLURM_JOB_NUM_NODES)) 

mpirun ./yourexe

#!/bin/bash
#SBATCH -N 4
#SBATCH --tasks-per-node 96

module load gcc/9.2.0 openmpi/gcc.9/3.1.5

tasks_per_node=${SLURM_TASKS_PER_NODE%\(*}
export OMP_NUM_THREADS=$(($tasks_per_node*$SLURM_JOB_NUM_NODES))

mpirun ./yourexe