[slurm-users] Reserving slots with sbatch and OpenMpi

[Mccall, Kurt E. (MSFC-EV41)]

With sbatch, what is the proper way to launch 5 tasks each on a single node, but reserve two slots on each node so that the original tasks can each create one new process using MPI_Comm_spawn?

I've tried various combinations of the sbatch arguments -nodes, --ntasks-per-node and -cpu-per-node, but all attempts result in this OpenMpi error message:

"All nodes which are allocated for this job are already filled."

I expected the proper arguments to be -nodes=5  --ntasks=5   -cpus-per-task=2.

The 5 original processes are created correctly, but it seems like MPI_Comm_spawn is causing the error message when it tries to allocate a CPU.

I'm using slurm 20.11.8 and OpenMpi 4.1.2.

Thanks,
Kurt

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