A Hybrid Shared Memory/Message Passing Parallel Machine

Current and emerging high-performance parallel com puter architectures generally implement one of two types of communication mechanisms: shared memory (SM) or message passing (MP). In this paper we propose a hybrid SM/MP architecture together with a hybrid SM/MP programming model, that we believe effectively combines the advantages of each system. The SM/MP architecture contains both a high-performance coherence protocol for shared memory, and message-passing primi tives that coexist with the coherence protocol but have no coherence overhead. The SM/MP programming model provides a framework for safely and effectively using the SM/MP communication primitives. We illustrate the use of the model and primitives to reduce communication overhead in SM systems.