Approximate data mapping in refresh-free DRAM for energy-efficient computing in modern mobile systems

Abstract

In the context of modern mobile and embedded communication systems, the increasing storage density of dynamic random access memory (DRAM) poses significant challenges in energy management, with DRAM refresh emerging as a major factor in energy consumption. Meanwhile, approximate computing is becoming an emerging energy-efficient paradigm for mobile and embedded systems involving the error-resilient applications of media processing, recognition, and data mining. This paper proposes to leverage approximate computing to eliminate all the unnecessary refreshes in DRAM and makes it as energy-efficient as “non-volatile” devices. The devised solution is based on the observation that mapping the virtual page of certain reusing distances into the memory rows of the particular retention time intervals can greatly decrease or even completely eliminate refresh operations for approximate computing workloads. In the proposed Non-Volatile DRAM (NV-DRAM), special page allocation and data mapping strategies have been developed for different types of systems to control the Quality of Result (QoR) of the system and best exploit the allowable quality margin (precision loss) for refresh removing. A static data mapping policy and a control-theory inspired PID controller are proposed to dynamically map approximate work-set to NV-DRAM rows without infringing the QoR constraint. The results show that the error rate of our predictive strategies can be controlled under 1%, and our proposal saves more than 99.9% of refresh energy consumption.