Energy Efficient Caching for Phase-Change Memory

Abstract

Phase-Change Memory (PCM) has the potential to replace DRAM as the primary memory technology due to its non-volatility, scalability, and high energy efficiency. However, the adoption of PCM will require technological solutions to surmount some deficiencies of PCM, such as writes requiring significantly more energy and time than reads. One way to limit the number of writes is by adopting a last-level cache replacement policy that is aware of the asymmetric nature of PCM read/write costs. We first develop a cache replacement algorithm, Asymmetric Landlord (AL), and show that it is theoretically optimal in that it gives the best possible guarantee on relative error. We also propose an algorithm Variable Aging (VA), which is a variation of AL. We have carried out a simulation analysis comparing the algorithms LRU, N-Chance, AL, and VA. For benchmarks that are a mixture of reads and writes, VA is comparable or better than N-Chance, even for the best choice of N, and uses at least 11% less energy than LRU. For read dominated benchmarks, we find that AL and VA are comparable to LRU, while N-Chance (using the N that was best for benchmarks that were a mixture of reads and writes) uses at least 20% more energy.