LimitLESS Directories: A Scalable Cache Coherence Scheme

Caches enhance the performance of multiprocessors by reducing network traffic and average memory access latency. However, cache-based systems must address the problem of cache coherence. We propose the LimitLESS directory protocol to solve this problem. The LimitLESS scheme uses a combination of hardware and software techniques to realize the performance of a full-map directory with the memory overhead of a limited directory. This protocol is supported by Alewife, a large-scale multiprocessor. We describe the architectural interfaces needed to implement the LimitLESS directory, and evaluate its performance through simulations of the Alewife machine. 1 Introduction The communication bandwidth of interconnection networks is a critical resource in large-scale multiprocessors. This situation will remain unchanged in the future because physically constrained communication speeds cannot match the increasing bandwidth requirements of processors. Caches reduce the volume of traffic imposed on..