Hello, Has anyone successfully used the homogeneous options in boost MPI before? I build boost mpi after uncommenting the appropriate line in the boost mpi config.cpp file and enabled BOOST_IS_BITWISE_SERIALIZABLE([classname]) for several of my classes that I pass, but I saw no change in performance, so I am not sure if it is enabled. The documentation says the following: More optimizations are possible on homogeneous machines, by avoiding MPI_Pack/MPI_Unpack calls but using direct bitwise copy. This feature can be enabled by defining the macro BOOST_MPI_HOMOGENEOUS when building Boost.MPI and when building the application. In addition all classes need to be marked both as is_mpi_datatype and as is_bitwise_serializable, by using the helper macro of Boost.Serialization: I defined the macro when building boost and marked the classes, but I could find no information anywhere on what to do when building the application, so I am thinking maybe this is what I am missing. Any help would be much appreciated. Thanks, Kyle