<no title> — Open MPI 5.0.0 documentation

Processes are mapped based on one of the following directives as applied at the job level:

- `SLOT` assigns procs to each node up to the number of available slots on that node before moving to the next node in the allocation

- `HWTHREAD` assigns a proc to each hardware thread on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `CORE` (default) assigns a proc to each core on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `L1CACHE` assigns a proc to each L1 cache on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `L2CACHE` assigns a proc to each L2 cache on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `L3CACHE` assigns a proc to each L3 cache on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `NUMA` assigns a proc to each NUMA region on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `PACKAGE` assigns a proc to each package on a node in a round-robin manner up to the number of available slots on that node before moving to the next node in the allocation

- `NODE` assigns processes in a round-robin fashion to all nodes in the allocation, with the number assigned to each node capped by the number of available slots on that node

- `SEQ` (often accompanied by the file=<path> qualifier) assigns one process to each node specified in the file. The sequential file is to contain an entry for each desired process, one per line of the file.

- `PPR:N`:resource maps N procs to each instance of the specified resource type in the allocation

- `RANKFILE` (often accompanied by the file=<path> qualifier) assigns one process to the node/resource specified in each entry of the file, one per line of the file.

- `PE-LIST=a,b` assigns procs to each node in the allocation based on the ORDERED qualifier. The list is comprised of comma-delimited ranges of CPUs to use for this job. If the ORDERED qualifier is not provided, then each node will be assigned procs up to the number of available slots, capped by the availability of the specified CPUs. If ORDERED is given, then one proc will be assigned to each of the specified CPUs, if available, capped by the number of slots on each node and the total number of specified processes. Providing the OVERLOAD qualifier to the “bind-to” option removes the check on availability of the CPU in both cases.

Any directive can include qualifiers by adding a colon (`:`) and any combination of one or more of the following (delimited by colons) to the `--map-by` option (except where noted):

- `PE=n` bind n CPUs to each process (can not be used in combination with rankfile or pe-list directives)

- `SPAN` load balance the processes across the allocation by treating the allocation as a single “super-node” (can not be used in combination with `slot`, `node`, `seq`, `ppr`, `rankfile`, or `pe-list` directives)

- `OVERSUBSCRIBE` allow more processes on a node than processing elements

- `NOOVERSUBSCRIBE` means `!OVERSUBSCRIBE`

- `NOLOCAL` do not launch processes on the same node as `prun`

- `HWTCPUS` use hardware threads as CPU slots

- `CORECPUS` use cores as CPU slots (default)

- `INHERIT` indicates that a child job (i.e., one spawned from within an application) shall inherit the placement policies of the parent job that spawned it.

- `NOINHERIT` means ``!INHERIT`

- `FILE=<path>` (path to file containing sequential or rankfile entries).

- `ORDERED` only applies to the `PE-LIST` option to indicate that procs are to be bound to each of the specified CPUs in the order in which they are assigned (i.e., the first proc on a node shall be bound to the first CPU in the list, the second proc shall be bound to the second CPU, etc.)

Note

Directives and qualifiers are case-insensitive and can be shortened to the minimum number of characters to uniquely identify them. Thus, `L1CACHE` can be given as `l1cache` or simply as `L1`.

The type of CPU (core vs hwthread) used in the mapping algorithm is determined as follows:

- by user directive on the command line via the HWTCPUS qualifier to the `--map-by` directive

- by setting the `rmaps_default_mapping_policy` MCA parameter to include the `HWTCPUS` qualifier. This parameter sets the default value for a PRRTE DVM — qualifiers are carried across to DVM jobs started via `prun` unless overridden by the user’s command line

- defaults to CORE in topologies where core CPUs are defined, and to hwthreads otherwise.

If your application uses threads, then you probably want to ensure that you are either not bound at all (by specifying `--bind-to none`), or bound to multiple cores using an appropriate binding level or specific number of processing elements per application process via the `PE=#` qualifier to the `--map-by` command line directive.

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