GfxDoctor: A Holistic Graphics Energy Profiler for Mobile Devices

Abstract

Graphics is one of the major energy drain sources in smartphone apps. To optimize the app graphics energy, however, developers face the challenge of highly complex graphics rendering process, which involves multiple system layers including the app, the framework, the GPU, and the asynchronous interactions among them. Current diagnostic tools can profile the resource usage from certain layers, but fall short in stitching together profiling information across all the layers which is needed to provide developers with the visual effect-energy tradeoff at the app source-code level. In this paper, we design and implement a holistic graphics energy diagnosis tool, GfxDoctor1, that helps developers to systematically diagnose energy inefficiencies in app graphics at the app source-code level, by precisely quantifying (1) the visual effect of each UI update, and (2) the aggregate energy drain spent in traversing the entire frame rendering stack due to each UI update. GfxDoctor overcomes three challenges faced in deriving per-UI-update visual effect and energy accounting, asynchrony across system layers, UI update batching, and "black-box" GPU, with two key techniques -- lightweight view-frame-ID-based information flow tracking, and OpenGL record-and-replay plus frame diffing. We show the effectiveness of GfxDoctor by profiling a randomly sampled set of 30 popular Android apps which reveals three types of graphics energy bugs happening in 8 out of the 30 apps. Removing these bugs reduces the app energy drain by 46% to 90%.