Making Write Less Blocking for Read Accesses in Phase Change Memory

Phase-change Memory (PCM) is a promising alternative or complement to DRAM for its non-volatility, scalable bit density, and fast read performance. Nevertheless, PCM has two serious challenges including extraordinarily slow write speed and less-than-desirable write endurance. While recent research has improved the write endurance significantly, slow write speed become a more prominent issue and prevents PCM from being widely used in real systems. To improve write speed, this paper proposes a new memory micro-architecture, called Parallel Chip PCM(PC2M), which leverages the spatial locality of memory accesses and trades bank-level parallelism for larger chip-level parallelism. We also present a micro-write scheme to reduce the blocking for read accesses caused by uninterrupted serialized writes. Micro-write breaks a large write into multiple smaller writes and timely schedules newly arriving reads immediately after a small write completes. Our design is orthogonal to many existing PCM write hiding techniques, and thus can be used to further optimize PCM performance. Based on simulation experiments of a multi-core processor under SPEC CPU 2006 multi-programmed workloads, our proposed techniques can reduce the memory latency of standard PCM by 68.5% and improve the system performance by 30.3% on average. PC2M and Micro-write significantly outperform existing approaches.