MultiScale: Memory System DVFS with Multiple Memory Controllers

The fraction of server energy consumed by the memory system has been increasing rapidly and is now on par with that consumed by processors. Recent work demonstrates that substantial memory energy can be saved with only a small, tightly-controlled performance degradation using memory Dynamic Frequency and Voltage Scaling (DVFS). Prior studies consider only servers with a single memory controller (MC); however, multicore server processors have begun to incorporate multiple MCs. We propose MultiScale, the first technique to coordinate DVFS across multiple MCs, memory channels, and memory devices. Under operating system control, MultiScale monitors application bandwidth requirements across MCs. It then uses a heuristic algorithm to select and apply a frequency combination that will minimize the overall system energy within user-specified per-application performance constraints. Our results demon-strate that MultiScale reduces system energy consumption significantly, compared to prior approaches, while respecting the user-specified performance constraints