Summary

• It is important to understand the semantics of MPI
• The send/receive calls provide for data synchronization, not necessarily process synchronization
• A correct MPI program cannot depend on buffering for messages
• For a highly optimized MPI program, it is important to use only few optimized subroutines from the MPI library, typically straight send/receive variants
• The SGI implementation of MPI uses N+1 processes in parallel region, therefore it is better for scalability to run MPI with smaller number of processors than physically available in the machine
• Proprietary Message Passing Libraries (I.e. SHMEM) perform better than MPI on the Origin, because MPI’s generic interface makes it much harder to optimize

Previous slide

Back to first slide

View graphic version