Fine-grained write scheduling for PCM performance improvement under write power budget

Phase-change memory (PCM) has gained much attention recently since it offers several advantages over DRAM, such as high cell density and low leakage power. PCM has similar read power and latency as DRAM; however, its write power and latency are significantly higher than DRAM. Therefore, one challenge with PCM is how to increase write throughput under write power budget constraints. To increase write concurrency, PCM often adopts division programming, where a write occurs in a series of divisions, so that writes to different banks proceed concurrently. In this study, we observe that since the write scheduling granularity in the memory controller differs from the actual write granularity in PCM chips, i.e., requests vs. divisions, the available power budget cannot be fully utilized. We therefore propose enhancing the interface between the memory controller and PCM chips to allow the memory controller to schedule writes in the division granularity. To further increase power budget utilization, we design a variable-length division mechanism to allow the division granularity to be adjusted at runtime according to the available write power budget. Our experimental results show that these techniques improve system performance by up to 65%.