how to limit the number of jobs running on the same node using SLURM?

Question

I have a job array of 100 jobs. I want at most 2 jobs from the job array can be allocated to the same node. How can I do this using SLURM? Thanks!

Answer 1

Assuming that jobs can share nodes, and that nodes have homogeneous configuration, and that you are alone on the cluster,

1. use the sinfo -Nl command to find the number of CPUs per nodes
2. submit jobs that request half that number with either of #SBATCH --tasks-per-node=... or #SBATCH --cpus-per-task=... based on what your jobs do

If you are administrating a cluster that is shared among other people, you can define GRES of a dummy type, and assign two of them to each node in slurm.conf and then request one per job with --gres=dummy:1