PAC-PLRU: A Cache Replacement Policy to Salvage Discarded Predictions from Hardware Prefetchers

Abstract

Cache replacement policy plays an important role in guaranteeing the availability of cache blocks, reducing miss rates, and improving applications' overall performance. However, recent research efforts on improving replacement policies require either significant additional hardware or major modifications to the organization of the existing cache. In this study, we propose the PAC-PLRU cache replacement policy. PAC-PLRU not only utilizes but also judiciously salvages the prediction information discarded from a widely-adopted stride prefetcher. The main idea behind PAC-PLRU is utilizing the prediction results generated by the existing stride prefetcher and preventing these predicted cache blocks from being replaced in the near future. Experimental results show that leveraging the PAC-PLRU with a stride prefetcher reduces the average L2 cache miss rate by 91% over a baseline system with only PLRU policy, and by 22% over a system using PLRU with an unconnected stride prefetcher. Most importantly, PAC-PLRU only requires minor modifications to existing cache architecture to get these benefits. The proposed PAC-PLRU policy is promising in fostering the connection between prefetching and replacement policies, and have a lasting impact on improving the overall cache performance.