Feedback EDF scheduling exploiting hardware-assisted asynchronous dynamic voltage scaling

Recent processor support for dynamic frequency and voltage scaling (DVS) allows software to affect power consumption by varying execution frequency and supply voltage on the fly. However, processors generally enter a sleep state while transitioning between frequencies/voltages. In this paper, we examine the merits of hardware/software co-design for a feedback DVS algorithm and a novel processor capable of executing instructions during frequency/voltage transitions. We study several power-aware feedback schemes based on earliest-deadline-first (EDF) scheduling that adjust the system behavior dynamically for different workload characteristics. An infrastructure for investigating several hard real-time DVS schemes, including our feedback DVS algorithm, is implemented on an IBM PowerPC 405LP embedded board. Architecture and algorithm overhead is assessed for different DVS schemes. Measurements on the experimentation board provide a quantitative assessment of the potential of energy savings for DVS algorithms as opposed to prior simulation work that could only provide trends. Energy consumption, measured through a data acquisition board, indicates a considerable potential for real-time DVS scheduling algorithms to lower energy up to 64 % over the naive DVS scheme. Our feedback DVS algorithm saves at least as much and often considerably more energy than previous DVS algorithms with peak savings of an additional 24 % energy reduction. To the best of our knowledge, this is the first comparative study of real-time DVS algorithms on a concrete micro-architecture and the first evaluation of asynchronous DVS switching.