Abstract

This paper investigates the performance of shared virtual memory protocols on large-scale multicomputers. Using experiments on a 64-node Paragon, we show that the traditional Lazy Release Consistency (LRC) protocol does not scale well, because of the large number of messages it requires, the large amount of memory it consumes for protocol overhead data, and because of the diculty of garbage collecting that data. To achieve more scalable performance, we introduce and evaluate two new protocols. The rst, Home-based LRC (HLRC), is based on the Automatic Update Release Consistency (AURC) protocol. Like AURC, HLRC maintains a home for each page to which all updates are propagated and from which all copies are derived. Unlike AURC, HLRC requires no specialized hardware support. We nd that the use of homes provides substantial improvements in performance and scalability over LRC. Our second protocol, called Overlapped Home-based LRC (OHLRC), takes advantage of the communication processor found on each node of the Paragon to ooad some of the protocol overhead of HLRC from the critical path followed by the compute processor. We nd that OHLRC provides modest improvements over HLRC. We also apply overlapping to the base LRC protocol, with similar results. Our experiments were done using ve of the Splash-2 benchmarks. We report overall execution times, as well as detailed breakdowns of elapsed time, message trac, and memory use for each of the protocols. 1

Citations