Verify that the proper interconnect and/or transport is used: check for environment variables controlling transport (see the section called “Controlling ParaStation MPI communication paths” and ps_environment(5)).
Watch protocol counters, e.g. counters indicating timeouts,
retries, errors or other bad conditions. For p4sock, check
recv_user. See the section called “ParaStation protocol p4sock”.
Look for a crystal bowl!