OMPI/MCA/PML/UCX: Set node local id.

[rakhmets]

Set mode local id hint for UCX context.
The parameter is introduced by openucx/ucx#10870.
The parameter does not affect semantics, only transport selection criteria and the resulting performance.

[devreal]

LGTM

[bosilca]

I'm really curious about how this can improve performance ? What assumptions are made about the rank that lead to better performance ?

[brminich]

I'm really curious about how this can improve performance ? What assumptions are made about the rank that lead to better performance ?

for instance we use it to support certain server configurations here
openucx/ucx#10870

[rhc54]

Just FWIW: if you think you might want to support dynamic operations (e.g., comm_spawn) or permit multiple jobs to share a node (e.g., when using a workload manager), then you might want to use the node rank of the process instead of the local rank to ensure each proc has a unique value. If only one job is executing, or if the environment fails to provide the node rank, then the local and node ranks are the same.