Using multiple energy gears in MPI programs on a power-scalable cluster

Recently, system architects have built low-power, high-performance clusters, such as Green Destiny. The idea behind these clusters is to improve the energy efficiency of nodes. However, these clusters save power at the expense of performance. Our approach is instead to use high-performance cluster nodes that are frequency- and voltage-scalable; energy can than be saved by scaling down the CPU. Our prior work has examined the costs and benefits of executing an entire application at a single reduced frequency.This paper presents a framework for executing a single application in several frequency-voltage settings. The basic idea is to first divide programs into phases and then execute a series of experiments, with each phase assigned a prescribed frequency. During each experiment, we measure energy consumption and time and then use a heuristic to choose the assignment of frequency to phase for the next experiment.Our results show that significant energy can be saved without an undue performance penalty; particularly, our heuristic finds assignments of frequency to phase that is superior to any fixed-frequency solution. Specifically, this paper shows that more than half of the NAS benchmarks exhibit a better energy-time tradeoff using multiple gears than using a single gear. For example, IS using multiple gears uses 9% less energy and executes in 1% less time than the closest single-gear solution. Compared to no frequency scaling, multiple gear IS uses 16% less energy while executing only 1% longer.