Shared Memory Versus Message Passing in a Tightly-Coupled Multiprocessor: A Case Study

Conceptually, the BBN Butterfly Parallel Processor can support a model of computation based on either shared memory or message passing. Recently, much of t.he work on the Butterfly, including finite element analysis and computer vision algorithms, has assumed the shared-memory model. In this paper we describe the results of our experiments with the message-passing model. The goal of the experiments was to analyze the tradeoffs between the shared-memory model, as exemplified by the BBN Uniform System package, and a simple message-passing model. Important factors to be considered were performance, scalability, and ease of programming. We compare the two models with respect to these criteria and conclude that the particular model of computation used is less important than how well it is matched to the application