Setting OMPI_MCA_btl_tcp_if_include=lo as default

[amckinstry]

Hi,

I have a question about OMPI_MCA_btl_tcp_if_include.

On Debian, we see a lot of warnings:

examl: btl_tcp_proc.c:266:mca_btl_tcp_proc_create_interface_graph] Unable to find reachable pairing between local and remote interfaces

These are I believe benign and due to the fact we're testing an MPI job on a single node: not its usual configuration. But they lead to a lot of false positives in automated tests.

My preferred answer is to set OMPI_MCA_btl_tcp_if_include=lo in openmpi-mca-params.conf. The logic is that the user expects to have to set configuration for a given run/machine but not have to rebuild any code; its trivial to edit/override the configuration.

The question is: is doing this benign, silencing a warning, or does it have deeper consequences?

Thanks
Alastair McKinstry