Effectiveness of Dynamic Prefetching in Multiple-Writer Distributed Virtual Shared-Memory Systems

We consider a network of workstations (NOW) organization consisting of bus-based multiprocessors interconnected by a high latency and high bandwidth interconnect, such as ATM, on which a shared-memory programming model using a multiple-writer distributed virtual shared-memory system is imposed. The latencies associated with bringing data into the local memory are a severe performance limitation of such systems. To make the access latencies tolerable, we propose a novel prefetch approach and show how it can be integrated into the software-based coherence layer of a multiple-writer protocol. This approach uses the access history of each page to guide which pages to prefetch. Based on detailed architectural simulations and seven scientific applications we find that our prefetch algorithm can remove a vast majority of the remote operations, which improves the performance of all applications. We also find that the bandwidth provided by ATM switches available today is sufficient to accommodate prefetching. However, the protocol processing overhead of available ATM interfaces limits the gain of the prefetching algorithms.