Reducing DRAM refresh power consumption by runtime profiling of retention time and dual-row activation

Refresh power of dynamic random-access memory (DRAM) has become a critical problem due to the large memory capacity of servers and mobile devices. It is imperative to reduce refresh rate in order to reduce refresh power consumption. However, current methods of refresh rate improvement have limitations such as large area/performance overhead, low system availability, and lack of support at the memory controller. We propose a novel scheme which comprises three essential functions: (1) an adaptive refresh method that adjusts refresh period on each DRAM chip, (2) a runtime method of retention-time profiling that operates inside DRAM chips during idle time thereby improving availability, and (3) a dual row activation method which improves weak cell retention time at a very small area cost. The proposed scheme allows each DRAM chip to refresh with its own refresh period without requiring the external support. Experiments based on real DRAM chip measurements show that the proposed methods can increase refresh period by 4.5 times at 58 degrees C by adjusting refresh period in a temperature-aware manner while incurring only a small overhead of 1.05% and 0.02% in DRAM chip area and power consumption, respectively. Below 58 degrees C, our method improves the refresh period by 12.5% compared with two state-of-the-art methods, AVATAR and in-DRAM ECC. In various memory configurations with SPEC benchmarks, our method outperforms the existing ones in terms of energy-delay product by 19.7% compared with the baseline, and by 15.4% and 12.4%, with respect to AVATAR and in-DRAM ECC, respectively. (C) 2019 Elsevier B.V. All rights reserved.