An Adaptive Coherence Protocol Using Write Invalidate and Write Update Mechanisms

Abstract

A number of different systems (multiprocessor systems, distributed systems, and nowadays Internet) replicate data (cache lines, pages, user defined data structures, and Internet objects) in order to improve the performance, but it introduces a coherence problem. Many different protocols have been introduced to maintain coherence between the copies of the same date item. The performance of such systems is very sensitive to both the data access behavior of the application and the coherence mechanism. Adaptive coherence protocols use a decision function to dy namically choose the appropriate coherence mechanism. The choice of coherence mechanism is determined from the data access behavior with the goal of improving performance. The decision function presented in this paper chooses between a write invalidate and a write update mechanism, depending on which of these mechanisms incurs a lower cumulative communication coherence overhead. Simul ation results are presented which demonstrate a significant improvement over other suggested solutions.