Characterizing display QoS based on frame dropping for power management of interactive applications on smartphones

User-centric power management in smartphones aims to conserve power without affecting user's perceived quality of experience. Most existing works focus on periodically updated applications such as games and video players and use a fixed frame rate, measured in frame per second (FPS), as the metric to quantify the display quality of service (QoS). The idea is to adjust the CPU/GPU frequency just enough to maintain the frame rate at a user satisfactory level. However, when applied to aperiodically-updated interactive applications, e.g. Facebook or Instagram, that draw the frame buffer at a varying rate in response to user inputs, such a power management strategy becomes too conservative. Based on real user experiments, we observe that users can tolerate a certain percentage of frame drops when running aperiodically updated applications without affecting their perceived display quality. Hence, we introduce a new metric to characterize display quality of service, called the frame drawn ratio (FDR), and propose a new CPU/GPU frequency governor based on the FDR metric. The experiments by real users show that the proposed governor can conserve 17.2% power in average when compared to the default governor, while maintaining the same or even better QoE rating.