Quick-and-Dirty: Improving Performance of MLC PCM by Using Temporary Short Writes

Low write performance is a major obstacle to the commercialization of MLC PCM. One opportunity for improving the latency of MLC PCM writes is to use fewer SET iterations in a single write. Unfortunately, the data written by these short writes have significantly shorter retention time and thus need frequent refreshes. As a result, it is impractical to use these short-latency, short-retention writes globally. In this paper, we analyze the temporal behavior of write operations in typical applications and propose Quick-and-Dirty (QnD), a lightweight scheme to improve the performance of MLC PCM. QnD dynamically performs the short-latency, short-retention write when write operations are bursty, and then uses short-latency, short-retention writes to mitigate the short retention problem when memory system is relatively quiet. Our experimental results show that QnD improves performance by 30.9% on geometric mean while still providing acceptable memory lifetime (7.58 years on geometric mean). We also provide sensitivity studies of the aggressiveness, memory coverage and granularity of QnD technique.