Application-Controlled Coherence Protocols for Scope Consistent Software DSMs

Abstract

To use the shared memory programming paradigm in distributed architectures where there is no physically shared memory, an abstraction must be created. This abstraction is known as Distributed Shared Memory (DSM). To reduce communication costs, DSM systems usually replicate data. This approach generates a coherence problem, which is generally solved by a memory coherence protocol. Unfortunately, it seems that there is no coherence protocol that achieves good performance for a large set of applications since the most appropriate coherence protocol depends on how the application accesses data. For this reason, it is interesting for a DSM system to provide multiple coherence protocols. This article presents and evaluates a low-overhead mechanism that allows a DSM application to choose among multiple coherence protocols. This mechanism was incorporated in JIAJIA, a DSM system that implements scope consistency with a write-invalidate protocol. Our results on some benchmarks show a significant reduction on the number of messages exchanged, leading to better performance results.