Managing the energy-delay tradeoff in mobile applications with tempus

Abstract

Energy-efficiency is a critical concern in continuously-running mobile applications, such as those for health and context monitoring. An attractive approach to saving energy in such applications is to defer the execution of delay-tolerant op- erations until a time when they would consume less energy. However, introducing delays to save power may have a detri- mental impact on the user experience. To address this prob- lem, we present Tempus, a new approach to managing the trade-off between energy savings and delay. Tempus saves power by enabling programmers to annotate power-hungry operations with states that specify when the operation can be executed to save energy. The impact of power manage- ment on timeliness is managed by associating delay bud- gets with objects that contain time-sensitive data. A static analysis and the run-time service ensure that power manage- ment policies will not delay an object more than its assigned budget. We demonstrate the expressive power of Tempus through a case study of optimizing two real-world applica- tions. Furthermore, laboratory experiments show that Tem- pus may effectively manage the energy-delay trade-off on re- alistic workloads. For example, in a news application, five Tempus annotations may be used to create a policy that re- duces the latency of downloading images 10 times compared to the original implementation without affecting energy con- sumption. Our experiments also indicate that the overhead of tracking budgets in Tempus is small.