The Green Index: A Metric for Evaluating System-Wide Energy Efficiency in HPC Systems

In recent years, the high-performance computing (HPC) community has recognized the need to design energy-efficient HPC systems. The main focus, however, has been on improving the energy efficiency of computation, resulting in an oversight on the energy efficiencies of other aspects of the system such as memory or disks. Furthermore, the energy consumption of the non-computational parts of a HPC system continues to consume an increasing percentage of the overall energy consumption. Therefore, to capture a more accurate picture of the energy efficiency of a HPC system, we seek to create a benchmark suite and associated methodology to stress different components of a HPC system, such as the processor, memory, and disk. Doing so, however, results in a potpourri of benchmark numbers that make it difficult to "rank" the energy efficiency of HPC systems. This leads to the following question: What metric, if any, can capture the energy efficiency of a HPC system with a single number? To address the above, we propose The Green Index (TGI), a metric to capture the system-wide energy efficiency of a HPC system as a single number. Then, in turn, we present (1) a methodology to compute TGI, (2) an evaluation of system-wide energy efficiency using TGI, and (3) a preliminary comparison of TGI to the traditional performance-to-power metric, i.e., floating-point operations per second (FLOPS) per watt.