Analyzing the Energy (Dis-) Proportionality of Scalable Interconnection Networks

Power consumption is one of the most important aspects regarding design and operation of large computing systems, such as High-Performance Computing (HPC) and cloud installations. Various hard constraints exist due to technical, economic and ecological reasons. We will show that interconnection networks contribute substantially to power consumption, even though their peak power rating is low compared to other components. Moreover, networks are still not energy-proportional, opposed to other components such as processors. In fact, network links consume the same amount of energy whether they are in use or not. In this work, we analyze the potential of power savings in high-performance direct interconnection networks. First, by analyzing the power consumption of today's network switches we find that network links contribute most to a switch's power, but they behave differently than other components like processors regarding possible power saving. We extend a OMNeT++ based interconnection network simulator with link power models to asses power savings. Our early experiments, based on traces of the NAMD and Graph500 applications show an immense potential for power saving, as we observe long inactivity periods. However, in order to design effective power saving strategies it is necessary to come to a detailed understanding of different hardware parameters. The transition time, which is the time required to reconfigure a link, could be crucial for most strategies. We see our OMNeT++ based, energy-aware simulator as a first step towards a deeper knowledge regarding such constraints.