You can’t have both exclusive access to a node and sharing, that makes no sense.  You see this on AWS as well – you can select either sharing a physical machine or not.  There is no “don’t share if possible, and share otherwise”.

 

Unless you configure SLURM to overcommit CPUs, by definition if you request all the CPUs in the machine, you will get exclusive access.  But if any of the CPUs are allocated, then your job won’t start.

 

One way you can improve this, is to configure SLURM to try to fill each node up with jobs first, before starting to schedule jobs to a new node.  This isn’t good for traditional HPC MPI jobs, but if your jobs are all multithreaded or single-threaded, this will work quite well, and will keep nodes free so that jobs which do actually require exclusive access are more likely to be scheduled.  This probably means (but others please correct me) that you DON’T want CR_LLN, and you probably do want CR_Pack_Nodes.

 

Tim