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
-- Tim Cutts Scientific Computing Platform Lead AstraZeneca
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From: Henrique Almeida via slurm-users slurm-users@lists.schedmd.com Date: Thursday, 1 August 2024 at 8:21 PM To: Laura Hild lsh@jlab.org Cc: slurm-users@lists.schedmd.com slurm-users@lists.schedmd.com Subject: [slurm-users] Re: With slurm, how to allocate a whole node for a single multi-threaded process? Hello, sharing would be unavoidable when all nodes are either fully or partially allocated. There will be cases of very simple background tasks occupying, for example, 1 hart in a machine.
On Thu, Aug 1, 2024 at 3:08 PM Laura Hild lsh@jlab.org wrote:
Hi Henrique. Can you give an example of sharing being unavoidable?
-- Henrique Dante de Almeida hdante@gmail.com
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