Hi Alan,

unfortunately, process placement in Slurm is kind of black magic for
sub-node jobs, i.e. jobs that allocate only a small number of CPUs of
a node.

I have recently raised a similar question here:

 https://support.schedmd.com/show_bug.cgi?id=19236

And the buttom line was, that to "really have control over task placement
you really have to allocate the node in --exclusive manner".

Best regards
Jürgen


* Alan Stange via slurm-users <slurm-users@lists.schedmd.com> [240607 14:52]:
> All,
>
> I have a very simple slurm cluster.  It's just a single system with 2
> sockets and 16 cores in each socket.  I would like to be able to submit
> a simple task into this cluster, and to have the cpus assigned to that
> task allocated round robin across the two sockets.   Everything I try is
> putting all the cpus for this single task on the same socket.
>
> I have not specified any CpuBind options in the slurm.conf file.   For
> example, if I try
>
> $ srun -c 4 --pty bash
>
> I get a shell prompt on the system, and can run
>
> $ taskset -cp $$
> pid 12345 current affinity list: 0,2,4,6
>
> and I get this same set of cpus no matter what options I try (the
> cluster is idle with no tasks consuming slots).
>
> I've tried various srun command line options like:
> --hint=compute_bound
> --hint=memory_bound
> various --cpubind options
> -B 2:2 -m block:cyclic and block:fcyclic
>
> Note that if I try to allocation 17 cpus, then I do get the 17th cpu
> allocated on the 2nd socket.
>
>
> What magic incantation is needed to get an allocation where the cpus are
> chosen round robin across the sockets?
>
> Thank you!
>
> Alan
>
>
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--
Jürgen Salk
Scientific Software & Compute Services (SSCS)
Kommunikations- und Informationszentrum (kiz)
Universität Ulm
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