Uncertainty-based scheduling: Energy-efficient ordering for tasks with variable execution time

Energy consumption reduction is today an important design issue for all kinds of digital systems. Offering both flexibility and efficient energy management, variable speed processor architectures are prefered for low energy consumption even in hard real-time systems. For this type of systems, the main approach consists in trading speed for lower energy while meeting all deadlines. For tasks with varying execution time, speed scheduling is most efficient if performed at run-time. This paper presents a new ordering technique for such tasks, that reduces the energy consumption resulting from the run-time speed scheduling. Without affecting the real-time behavior, our Uncertainty-Based Scheduling (UBS) is a low complexity but energy-efficient method that can be applied on top of already existent real-time scheduling techniques, such as EDF. These claims are backed up by extensive simulation results accompanied by measurements on a platform based oil an Intel i80200 XScale processor.