EFGR: An Enhanced Fine Granularity Refresh Feature for High-Performance DDR4 DRAM Devices

摘要

High-density DRAM devices spend significant time refreshing the DRAM cells, leading to performance drop. The JEDEC DDR4 standard provides a Fine Granularity Refresh (FGR) feature to tackle refresh. Motivated by the observation that in FGR mode, only a few banks are involved, we propose an Enhanced FGR (EFGR) feature that introduces three optimizations to the basic FGR feature and exposes the bank-level parallelism within the rank even during the refresh. The first optimization decouples the nonrefreshing banks. The second and third optimizations determine the maximum number of nonrefreshing banks that can be active during refresh and selectively precharge the banks before refresh, respectively. Our simulation results show that the EFGR feature is able to recover almost 56.6% of the performance loss incurred due to refresh operations.