Prefetching effect on software shared memory over VIA

Abstract

In this paper we propose and evaluate the Adaptive prefetching technique for Software DSM (Software-based Distributed Shared-Memory) systems over three different communication layers on top of Myrinet an Interconnection Network. Use of a User-Level Communication Layer provides us a low-overhead and high-bandwidth that make it possible to analyze the prefetching effect on Software DSM systems using high performance network. GM-VIA and S-VIA are two User-Level Communication Layers proposed for this paper to analyze prefetching effect on Software DSM systems. And for comparison raisons, and since most of all previous existing works on prefetching for DSM were tested on a traditional communication protocol TCP/IP, we also propose an implementation of TCP/IP over GM that provides the same quality of message delivery as a TCP/IP but on the top of Myrinet. Adaptive Prefetching Technique improves the performance for regular parallel applications running on Software DSM system by using past history of memory access faults to adapt between the phase mode and stride mode. This technique doesn’t issue prefetches during periods when the application is behaving irregularly. The experimental results obtained on two Splash-2 applications show that prefetching can provide more performance improvement with S-VIA than other communication layers even if GM-VIA provides more speedup than S-VIA when no prefetching is issued. Our main conclusion is that prefetching techniques have to be taken in consideration by software designers as an effective way of tolerating the overhead of remote data accesses even when high interconnection network is used. In term of overall performance the Adaptive Prefetching Technique can provides speedup improvements as significant as 10% on 8 processors with S-VIA.