The Case for Energy-Proportional Computing

The Green Data Center Blog today pointed me to December's Cover Feature of Computer, the IEEE Computer Society's magazine. In it, authors Luiz André Barroso (distinguished engineer at Google) and Urs Hölzle (senior vice president of operations at Google and a Google Fellow) point out "Energy-proportional designs would enable large energy savings in servers, potentially doubling their efficiency in real-life use. Achieving energy proportionality will require significant improvements in the energy usage profile of every system component, particularly the memory and disk subsystems."

The two are making the case not only for server power management, but are calling on vendors to go a step further, to make computers adapt their consumptive ranges directly to the compute load consumed. This would be highly complementary to consolidation efforts currently underway.

In conclusion, the paper says,

• Servers and desktop computers benefit from much of the energy-efficiency research and development that was initially driven by mobile devices' needs. However, unlike mobile devices, which idle for long periods, servers spend most of their time at moderate utilizations of 10 to 50 percent and exhibit poor efficiency at these levels. Energy-proportional computers would enable large additional energy savings, potentially doubling the efficiency of a typical server. Some CPUs already exhibit reasonably energy-proportional profiles, but most other server components do not.
• We need significant improvements in memory and disk subsystems, as these components are responsible for an increasing fraction of the system energy usage. Developers should make better energy proportionality a primary design objective for future components and systems. To this end, we urge energy-efficiency benchmark developers to report measurements at nonpeak activity levels for a more complete characterization of a system's energy behavior

Among a few scholarly pieces from Google, the report also cites two great references; one, the US EPA's Report to Congress on Data Center Efficiency, and the other is one of many fine works by Jonathan Koomey, "Estimating Total Power Consumption by Servers in the U.S. and the World"