Evaluation of the implementation cost of cache coherence protocols using omniscient actions

Abstract

International audienceThis paper presents a novel simulation-based approach which targets the performance estimation of cache coherence protocol implementations. Our approach allows to model a cache coherence protocol where coherence transactions take zero cycle and do not generate communication accesses, in the hope that it will provide a close lower bound on latency and traffic. The protocol modeling approach relies on cycle-accurate simulation models in which components can access instantaneously and transparently internal states of other components. Using this strategy, the access time and the traffic due to cache misses are taken into account as it would be on a multiprocessor system without cache coherence. However, the proposed approach still ensures that processors receive coherent data. We detail the implementation of this approach in a cycle accurate multiprocessor simulation environment. To show its effectiveness, we implement cache and memory models for two coherence protocols both with and without our omniscient cache coherence (OCC) proposal. We show with a formal method that this approach makes it possible to preserve the consistency models implied by the cache coherence protocols, and experimentally that the OCC strategy protocol gives a close lower bound on latency and traffic