Energy-aware Scheduling of Multi-version on Heterogeneous Real-time Systems

The emergence of battery-powered devices has led to an increase of interest in the energy consumption of computing devices. For embedded systems, dispatching the workload on different computing units enables the optimisation of the overall energy consumption on high-performance heterogeneous platforms. However, to use the full power of heterogeneity, architecture specific binary blocks are required, each with different energy/time trade-offs. Finding a scheduling strategy that minimises the energy consumption, while guaranteeing timing constraints creates new challenges. These challenges can only be met by using the full heterogeneous capacity of the platform (e.g. heterogeneous CPU, GPU, DVFS, dynamic frequency changes from within an application). We propose an off-line scheduling algorithm for dependent multi-version tasks based on Forward List Scheduling to minimise the overall energy consumption. Our heuristic accounts for Dynamic Voltage and Frequency Scaling (DVFS) and enables applications to dynamically adapt voltage and frequency during run time. We demonstrate the benefits of multi-version task models coupled with an energy-aware scheduler. We observe that selecting the most energy efficient version for each task does not lead to the lowest energy consumption for the whole application. Then we show that our approach produces schedules that are on average 45.6% more energy efficient than schedules produced by a state-of-the-art scheduling algorithm. Next we compare our heuristic against an optimal solution derived by an Integer Linear Programming (ILP) formulation (deviation of 1.6% on average). Lastly, we empirically show that the energy consumption predicted by our scheduler is close to the actual measured energy consumption on a Odroid-XU4 board (at most -15.8%).