3.5. General Run-Time Support Notes
The Open MPI installation must be in your
PATHon all nodes (and potentiallyLD_LIBRARY_PATHorDYLD_LIBRARY_PATH, iflibmpi/libshmemis a shared library), unless using the--prefixor--enable-mpirun-prefix-by-defaultfunctionality (see below).Open MPI’s run-time behavior can be customized via Modular Component Architecture (MCA) parameters (see this section) for more information on how to get/set MCA parameter values). Some MCA parameters can be set in a way that renders Open MPI inoperable. In particular, some parameters have required options that must be included:
If specified, the
btlparameter must include theselfcomponent, or Open MPI will not be able to deliver messages to the same rank as the sender. For example:mpirun --mca btl tcp,self ...If specified, the
btl_tcp_if_excludeparameter must include the loopback device (loon many Linux platforms), or Open MPI will not be able to route MPI messages using the TCP BTL. For example:mpirun --mca btl_tcp_if_exclude lo,eth1 ...
Running on nodes with different endian and/or different datatype sizes within a single parallel job is supported in this release. However, Open MPI does not resize data when datatypes differ in size (for example, sending a 4 byte
MPI_DOUBLEand receiving an 8 byteMPI_DOUBLEwill fail).