Active low-power modes for main memory

Main memory is responsible for a significant fraction of the energy consumed by servers. Prior work has focused on exploiting memory low-power states to conserve energy. However, these states require entire ranks of DRAM to be idle, which is difficult to achieve even in lightly loaded servers. In this work, we propose three techniques for exploiting active low-power modes to conserve full-system energy, while remaining within user-prescribed performance bounds. The first technique, called MemScale, creates active memory system low-power modes by applying dynamic voltage and frequency scaling to the memory controller and dynamic frequency scaling to the memory channels and DRAM devices. The second technique, called CoScale, coordinates the CPU and main memory active low-power modes to avoid instability and increase energy savings. The third technique, called MultiScale, tackles servers with multiple memory controllers, by coordinating the active low-power modes across the controllers. Our extensive results demonstrate that the three techniques reduce full-system energy consumption significantly, compared to prior approaches, while consistently remaining within the user-prescribed performance bounds. We conclude that the potential benefits of those three mechanisms and policies more than compensate for their small hardware cost.Ph. D.Includes bibliographical referencesby Qingyuan Den