A reuse-based refresh policy for energy-aware eDRAM caches

Abstract

DRAM technology requires refresh operations to be performed in order to avoid data loss due to capacitance leakage. Refresh operations consume a significant amount of dynamic energy, which increases with the storage capacity. To reduce this amount of energy, prior work has focused on reducing refreshes in off-chip memories. However, this problem also appears in on-chip eDRAM memories implemented in current low-level caches. The refresh energy can dominate the dynamic consumption when a high percentage of the chip area is devoted to eDRAM cache structures. Replacement algorithms for high-associativity low-level caches select the victim block avoiding blocks more likely to be reused soon. This paper combines the state-of-the-art MRUT replacement algorithm with a novel refresh policy. Refresh operations are performed based on information produced by the replacement algorithm. The proposed refresh policy is implemented on top of an energy-aware eDRAM cache architecture, which implements bank-prediction and swap operations to save energy. Experimental results show that, compared to a conventional eDRAM design, the proposed energyaware cache can achieve by 72% refresh energy savings. Considering the entire on-chip memory hierarchy consumption, the overall energy savings are 30%. These benefits come with minimal impact on performance (by 1.2%) and area overhead (by 0.4%). 2014 Elsevier B.V. All rights reserved.