Revisiting Server Energy Proportionality

Server energy proportionality refers to a proposed ideal that a server consumes energy proportional to its utilization level. Since its introduction in 2007, the ideal has been adopted by the server industry as a design goal to further optimize the energy efficiency of their servers. There have also been studies on how energy proportionality has evolved over time. However, most of these efforts assume linear proportionality. Must energy proportionality be linear? In this paper we look into this problem. We analyze 410 SPECpower_ssj2008 benchmark results published from 2007 to 2012, and find that modern servers have pushed server energy proportionality from linear to quadratic. We also observe a strong correlation in time between this change and dynamic over-clocking (such as Intel Turbo Boost). We present all these findings in the paper, along with discussions on the implications of super-linearity in server energy proportionality.