Data-aware DRAM refresh to squeeze the margin of retention time in hybrid memory cube

Abstract

With the increase of storage density, DRAM refresh leads to higher overhead of power and bandwidth, particularly in emerging 3D stacked memory design like Hybrid Memory Cube (HMC). To exploit the hardware resources for a smarter solution, we propose a data-aware refresh control scheme, Trial and Error (Trial-n-Error), which leverages the data-pattern dependence characteristics of the cells' retention time to reduce refresh operations. Trial-n-Error is a systematic approach that employs our proposed Synergy Testing to capture the refresh bottleneck of DRAM memory: “weak” cells that have a relatively shorter retention time. By locating the dominant weak cells sensitized by applications, Trial-n-Error can avoid the worst-case refresh setting, and adjust the refresh rate under the control of our self-tuning algorithm. Thus, Trial-n-Error can gradually approach to the possible lower-bound of refresh rate for less energy and memory bandwidth consumption. In experiments of 3D-stacked DRAMs, we successfully eliminate an average of 28% refresh operations and save 21% refresh energy for a set of pre-profiled synthetic data patterns and real benchmarks.