<no title> — Open MPI 5.0.0 documentation

PRRTE automatically ranks processes for each job starting from zero. Regardless of the algorithm used, rank assignments span applications in the same job — i.e., a command line of

    -n 3 app1 : -n 2 app2

will result in `app1` having three processes ranked 0-2 and `app2` having two processes ranked 3-4.

By default, process ranks are assigned in accordance with the mapping directive — e.g., jobs that are mapped by-node will have the process ranks assigned round-robin on a per-node basis. However, users can override the default by specifying any of the following directives using the `--rank-by` command line option:

- `SLOT` assigns ranks to each process on a node in the order in which the mapper assigned them. This is the default behavior, but is provided as an explicit option to allow users to override any alternative default specified in the environment. When mapping to a specific resource type, procs assigned to a given instance of that resource on a node will be ranked on a per-resource basis on that node before moving to the next node.

- `NODE` assigns ranks round-robin on a per-node basis

- `FILL` assigns ranks to procs mapped to a particular resource type on each node, filling all ranks on that resource before moving to the next resource on that node. For example, procs mapped by `L1cache` would have all procs on the first `L1cache` ranked sequentially before moving to the second `L1cache` on the node. Once all procs on the node have been ranked, ranking would continue on the next node.

- `SPAN` assigns ranks round-robin to procs mapped to a particular resource type, treating the collection of resource instances spanning the entire allocation as a single “super node” before looping around for the next pass. Thus, ranking would begin with the first proc on the first `L1cache` on the first node, then the next rank would be assigned to the first proc on the second `L1cache` on that node, proceeding across until the first proc had been ranked on all `L1cache` used by the job before circling around to rank the second proc on each object.

The `rank-by` command line option has no qualifiers.

Note

Directives are case-insensitive. `SPAN` is the same as `span`.

A more detailed description of the mapping, ranking, and binding procedure can be obtained via the `--help placement` option.