Why Race-to-Finish is Energy-Inefficient for Continuous Multimedia Workloads

It is often believed that a "race-to-finish" approach, where processing is finished quickly, is the best way to conserve energy on modern mobile architectures. However, from earlier work we know that for continuous multimedia workloads, the best way to conserve energy is to minimise processor frequency such that application deadlines are met. In this paper, we investigate the reasons behind this. We develop an original method to model dynamic and static power on individual power rails of the Tegra K1 by only measuring the total power usage of the board. Our model has an average error of only 8 %. We find that the way an application scales performance with frequency is very important for energy efficiency. We demonstrate a 37 % energy saving by minimising processor and memory frequency of a video processing filter such that a framerate of 20 FPS is met.