EqualWrites: Reducing Intra-Set Write Variations for Enhancing Lifetime of Non-Volatile Caches

Driven by the trends of increasing core-count and bandwidth-wall problem, the size of last level caches has greatly increased, and hence the researchers have explored non-volatile memories (NVMs) that provide high density and consume low-leakage power. Since NVMs have low write endurance and the existing cache management policies are write variation (WV) unaware, effective wear-leveling techniques (WLTs) are required for achieving reasonable cache lifetimes using NVMs. We present EqualWrites, a technique for mitigating intra-set WV. Our technique works by recording the number of writes on a block and changing the cache-block location of a hot data item to redirect the future writes to a cold block to achieve wear leveling. Simulation experiments have been performed using an x86-64 simulator and benchmarks from SPEC06 and high-performance computing field. The results show that for single-, dual-, and quad-core system configurations, EqualWrites improves cache lifetime by 6.31× , 8.74×, and 10.54×, respectively. In addition, its implementation overhead is very small and it provides larger improvement in lifetime than three other intra-set WLTs and a cache replacement policy.