On energy-constrained real-time scheduling

In this paper, we explore the feasibility and performance optimization problems for real-time systems that must remain functional during an operation/mission with a fixed, initial energy budget. We show that the feasibility problem is NP-hard in the context of systems with dynamic voltage scaling (DVS) capability and discrete speed levels. Then, we focus on energy-constrained periodic task systems where the available energy budget is not sufficient to meet all the deadlines. We propose techniques to maximize the total number of deadlines met and the total reward (utility) while guaranteeing the completion of the mission and a minimum performance for each task. We consider separately: (i) systems with or without DVS capability, and (ii) off-line (static) and on-line (dynamic) solutions to select most valuable jobs for execution. We also discuss the tractability of the involved optimization problems. Our on-line algorithms combine job promotion, job demotion and speed reduction techniques to maximize the system performance while guaranteeing the completion of the mission. We evaluate our schemes through simulations and show that the on-line schemes can yield significant performance improvements over static solutions.