Measuring QoE of interactive workloads and characterising frequency governors on mobile devices

Mobile computing devices such as smartphones and tablets have become tightly integrated with many people´s life, both at work and at home. Users spend large amounts of time interacting with their mobile device and demand an excellent user experience in terms of responsiveness, whilst simultaneously expecting a long battery life between charging cycles. Frequency governors, responsible for increasing or decreasing the Cpu clock frequency depending on the current workload and external events, try to balance the two contrasting goals of high performance and low energy consumption. However, despite their critical role in providing energy efficiency it is difficult to measure the effectiveness of frequency governors in an interactive environment. In this paper we develop a novel methodology for creating repeatable, fully automated, realistic, workloads that can accurately measure time lag in interactive applications resulting from non-optimally selected operating frequencies. We also introduce a new metric capturing the user experience for different Android frequency governors. We evaluate interactive workloads to demonstrate how our approach enables us to automatically record and replay sequences of user interactions for different system configurations. We demonstrate that none of the available Android frequency governors performs particularly well, but leave substantial room for improvement. We show that energy savings of up to 27% are possible, whilst delivering a user experience that is better than that provided by the standard Android frequency governor. We also show that it is possible to save 47% energy with performance that is indistinguishable from permanently running the Cpu at the highest frequency.