[slurm-users] Reserving cores without immediately launching tasks on all of them

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

I want to launch an MPICH job with sbatch with one task per node (each a manager), while also reserving a certain number of cores on each node for the managers to fill up with spawned workers (via MPI_Comm_spawn).   I'd like to avoid using -exclusive.

I tried the arguments -ntasks=20 -cpus-per-task=24, but it appears that 20 * 24 tasks will be launched.   Is there a way to reserve cores without immediately launching tasks on them?   Thanks for any help.

sbatch: defined options
sbatch: -------------------- --------------------
sbatch: cpus-per-task       : 24
sbatch: ignore-pbs          : set
sbatch: ntasks              : 20
sbatch: test-only           : set
sbatch: verbose             : 1
sbatch: -------------------- --------------------
sbatch: end of defined options
sbatch: Linear node selection plugin loaded with argument 4
sbatch: select/cons_res loaded with argument 4
sbatch: Cray/Aries node selection plugin loaded
sbatch: select/cons_tres loaded with argument 4
sbatch: Job 34274 to start at 2021-11-25T12:15:05 using 480 processors on nodes n[001-020] in partition normal
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