BRC Cluster Workshop

On the old cluster SLURM was configured so that it tracked allocated cores on each node, but did not limit a job from using more cores than specified in the submission i.e. a job could be submitted with the default 1-core allocation but run a program that started 10 threads and actually start using 10 cores. This occasionally led to nodes being bogged down.

On the new cluster jobs will have access to exactly as many cores as requested in the job submission. If you submit a job requesting 1 core, and start a program that uses 10 threads, all 10 threads will be time-sliced on 1 core. Your job might run something like 10 times slower than you expected it to.

So, you should be more careful in specifying how many cores your job needs. See the “-c” or “–cpus-per-task” option to sbatch.