SNOW: A State-Less Low-Overhead All Software Distributed Shared Memory System

Research in user-level communication and the recent increase in network speeds requires re-evaluation of traditional distributed shared memory (DSM) protocols for workstation networks. Our experience with a release consistency (RC) DSM system shows that the system has: (1) high protocol processing overhead, (2) high coherence related overhead, and (3) high software access control overhead. To reduce these overheads, in this paper we present a state-less DSM system based on the following features: (1) xed ownership, (2) data layout, (3) read-only data cache, (4) write-buuer for updates, and (5) a hybrid coherence protocol. Our results were obtained by executing a set of four benchmark applications that we ported to run on SNOW DSM system. The system executes the applications on a simulated architecture and the applications diier from each other in sharing pattern, computation granularity and amount of synchronization. In this paper we show an execution graph and a comparison graph for each application. We compared the performance of SNOW with a traditional update-based system and our results show that the traditional system can copy upto 6 times more data and can send upto 5 times more communication messages. The performance gains are because of the xed ownership protocol. The protocol reduces the software access detection, the write-shared protocol processing, and the consistency related communication overheads.