Graphics-intensive mobile games place different and varying levels of demand on the associated central processing units (CPUs) and graphics processing units (GPUs). In contrast to the workload variability that characterizes games, the current design of the energy governor employed by mobile systems appears to be outdated. In this paper, we review the energy-saving mechanism implemented in an Android system coupled with graphics-intensive gaming workloads from three perspectives: 1) user perception; 2) application status; and 3) the interplay between the CPU and GPU. We observe that there are information gaps in the current system, which may result in unnecessary energy wastage. To resolve the problem, we propose an online user-centric CPU-GPU governing framework. To bridge the identified information gaps, we classify rendered game frames into redundant/changing frames to satisfy user demand, categorize an application into GPU sensitive/insensitive phases to understand the application's demand, and determine the frequency scaling intents of the CPU and GPU to capture processor demand. In response to the measured demand, we employ a required workload estimator, a unified policy selector, and a frequency-scaling intent communicator in the framework to save energy. The proposed framework was implemented on an LG Nexus 5X smartphone, and extensive experiments with real-world 3-D gaming applications were conducted. According to the experiment results, for an application which is low interactive and infrequent phase changing, the proposed framework can, respectively, reduce energy consumption by 25.3% and 39% compared with our previous work and Android governors while maintaining user experience.
