<no title> — Open MPI 5.0.0 documentation

By default, processes are bound to individual CPUs (either COREs or HWTHREADs, as defined by default or by user specification for the job). On nodes that are OVERSUBSCRIBEd (i.e., where the number of procs exceeds the number of assigned slots), the default is to not bind the processes.

Note

Processes from prior jobs that are already executing on a node are not “unbound” when a new job mapping results in the node becoming oversubscribed.

Binding is performed to the first available specified object type within the object where the process was mapped. In other words, binding can only be done to the mapped object or to a resource located beneath that object.

An object is considered completely consumed when the number of processes bound to it equals the number of CPUs within it. Unbound processes are not considered in this computation. Additional processes cannot be mapped to consumed objects unless the `OVERLOAD` qualifier is provided via the `--bind-to` command line option.

Note that 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`.

Supported binding directives include:

- `NONE` does not bind the processes

- `HWTHREAD` binds each process to a single hardware thread/ This requires that hwthreads be treated as independent CPUs (i.e., that either the `HWTCPUS` qualifier be provided to the `map-by` option or that `hwthreads` be designated as CPUs by default).

- `CORE` binds each process to a single core. This can be done whether `hwthreads` or `cores` are being treated as independent CPUs provided that mapping is performed at the core or higher level.

- `L1CACHE` binds each process to all the CPUs in an `L1` cache.

- `L2CACHE` binds each process to all the CPUs in an `L2` cache

- `L3CACHE` binds each process to all the CPUs in an `L3` cache

- `NUMA` binds each process to all the CPUs in a `NUMA` region

- `PACKAGE` binds each process to all the CPUs in a `PACKAGE`

Any directive can include qualifiers by adding a colon (:) and any combination of one or more of the following to the `--bind-to` option:

- `OVERLOAD` indicates that objects can have more processes bound to them than CPUs within them

- `IF-SUPPORTED` indicates that the job should continue to be launched and executed even if binding cannot be performed as requested.

Note

Directives and qualifiers are case-insensitive. `OVERLOAD` is the same as `overload`.