Where is the energy spent inside my app?Fine Grained Energy Accounting on Smartphones with Eprof

摘要

Where is the energy spent inside my app? Despite the im-mense popularity of smartphones and the fact that energy is the most crucial aspect in smartphone programming, the answer to the above question remains elusive. This paper first presents eprof, the first fine-grained energy profiler for smartphone apps. Compared to profiling the runtime of ap-plications running on conventional computers, profiling en-ergy consumption of applications running on smartphones faces a unique challenge, asynchronous power behavior, where the effect on a component's power state due to a pro-gram entity lasts beyond the end of that program entity. We present the design, implementation and evaluation of eprof on two mobile OSes, Android and Windows Mobile. We then present an in-depth case study, the first of its kind, of six popular smartphones apps (including Angry-Birds, Faeebook and Browser). Eprof sheds lights on inter-nal energy dissipation of these apps and exposes surprising findings like 65%-75% of energy in free apps is spent in third-party advertisement modules. Eprof also reveals sev-eral "wakelock bugs", a family of "energy bugs" in smart-phone apps, and effectively pinpoints their location in the source code. The case study highlights the fact that most of the energy in smartphone apps is spent in I/O, and I/O events are clustered, often due to a few routines. This motivates us to propose bundles, a new accounting presentation of app I/O energy, which helps the developer to quickly understand and optimize the energy drain of her app. Using the bundle pre-sentation, we reduced the energy consumption of four apps by 20% to 65%.