Summary & Conclusions

MPI wasn't designed for the Cell Broadband Engine. A common MPI-node has one or more normal CPUs and several GBytes of RAM. The Cell Broadband Engine features a normal CPU (the PPU) and several special processing units with only a very limited amount of memory. The SPUs support only one thread per SPU and a complex handling of system-calls is needed. Because of this there are several restrictions in implementing MPI on the Cell Broadband Engine.

Nevertheless MPI on Cell makes sense. It greatly simlifies programming on the Cell Broadband Engine, features a public API which is well known and widely used and message passing operations are generally easier to use than DMA (DMA needs memory-addresses and explicit synchronization, whereas MPI only needs the ranks of participating processes and features implicit synchronization).

But message parsing operations cannot replace DMA. Both methods of communication have their advantages and disadvantages and they complement one another. So this library additionally features some easy to use DMA operations, if someone wants to gain maximum performance. Using DMA alltogether with send-recv especially speeds up application with a lot of communication going on between SPUs and PPU.