[slurm-users] MPI jobs via mirun vs. srun through PMIx.

[Philip Kovacs]

>according to https://slurm.schedmd.com/mpi_guide.html I have built
>Slurm 19.05 with PMIx support enabled and it seems to work for both,
>OpenMPI and Intel MPI. (I've also set MpiDefault=pmix in slurm.conf.)

>But I still don't get the point. Why should I favour `srun ./my_mpi_program´ 
>over `mpirun ./my_mpi_program´? For me, both seem to do exactly the same 
>thing. No? Did I miss something?

>Best regards
>Jürgen

Running a single job in isolation doesn't properly illustrate what slurm does in the larger sense.How do you fairly allocate and constrain the resources of an HPC installation when 1,000 jobs needto run, not just 1?  How do you schedule the jobs?  How do you keep track of the resources used sothat charge-back or billing can occur?  It's not about the ant -- it's about the colony.
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