What are MCA Parameters? Why would I set them?
MCA parameters are a way to tweak Open MPI’s behavior at run-time. For example, MCA parameters can specify: • Which interconnect networks to use • Which interconnect networks not to use • The size different between eager sends and rendezvous protocol sends • How many registered buffers to pre-pin (e.g., for GM or mVAPI) • The size of the pre-pinned registered buffers • …etc. It can be quite valuable for a system administrator to play with such values a bit and find an “optimal” setting for a particular operating environment. These values can then be set in a global text file that all users will, by default, inherit when then run Open MPI jobs. For example, say that you have a cluster with 2 ethernet networks — one for NFS and other system-level operations, and one for MPI jobs. The system administrator can tell Open MPI to not use the NFS TCP network at a system level, such that when users invoke mpirun or mpiexec to launch their jobs, they will automatically only be using the netwo
