CRP: Conditional Replacement Policy for Reliability Enhancement of STT-MRAM Caches

Driven by the trends of emerging technologies in on-chip memories, with increasing the size of last-level caches (LLCs), spin-transfer torque magnetic random access memories (STT-MRAMs) are the most promising alternative technology among the non-volatile memories (NVMs) to replace SRAMs. Despite their high density, scalability, and near-zero leakage power, the reliability of STT-MRAM LLCs is threatened by a high error rate due to their stochastic switching behavior. The error rate is highly influenced by the cache management, which necessitates redesigning the cache replacement policy based on the error behavior. In this article, we propose an error-aware cache replacement policy, namely, conditional replacement policy (CRP), to improve the reliability of STT-MRAM caches by decreasing the rate of both read disturbance and write failure. This is ascertained by nominating an appropriate data block in the cache to be replaced with an incoming data block, considering the minimum error rate. Moreover, the performance and latency of both write and read operations are considered. The simulation results show that compared with the state-of-the-art replacement policy in STT-MRAM caches, CRP reduces the total error rate by 68%. In addition, the proposed policy enhances the performance by 2% and saves energy consumption by 19%, on average. Meanwhile, the total number of writes is decreased by 41% compared with the previous scheme.