2014 Reports

Energy Exchanges: Internal Power Oversight for Applications

Kambadur, Melanie Rae; Kim, Martha Allen

This paper introduces energy exchanges, a set of abstractions that allow applications to help hardware and operating systems manage power and energy consumption. Using annotations, energy exchanges dictate when, where, and how to trade performance or accuracy for power in ways that only an application's developer can decide. In particular, the abstractions offer audits and budgets which watch and cap the power or energy of some piece of the application. The interface also exposes energy and power usage reports which an application may use to change its behavior. Such information complements existing system-wide energy management by operating systems or hardware, which provide global fairness and protections, but are unaware of the internal dynamics of an application. Energy exchanges are implemented as a user-level C++ library. The library employs an accounting technique to attribute shares of system-wide energy consumption (provided by system-wide hardware energy meters available on newer hardware platforms) to individual application threads. With these per-thread meters and careful tracking of an application's activity, the library exposes energy and power usage for program regions of interest via the energy exchange abstractions with negligible runtime or power overhead. We use the library to demonstrate three applications of energy exchanges: (1) the prioritization of a mobile game's energy use over third-party advertisements, (2) dynamic adaptations of the framerate of a video tracking benchmark that maximize performance and accuracy within the confines of a given energy allotment, and (3) the triggering of computational sprints and corresponding cooldowns, based on time, system TDP, and power consumption.