Multi-version scheduling in rechargeable energy-aware real-time systems

In the context of battery-powered real-time systems, three constraints need to be addressed: energy, deadlines and task rewards. Many future real-time systems will count on different software versions, each with different rewards, time and energy requirements, to achieve a variety of QoS-aware tradeoffs. We first propose a solution that allows the device to run the most valuable task versions while still meeting all deadlines and without depleting a given energy budget. Assuming that the energy budget can be replenished by using a rechargeable battery, we also propose (i) a static solution that maximizes the system value assuming a worst-case scenario (i.e., worst-case battery recharging/discharging conditions, as well as worst-case task execution times); and (ii) a dynamic scheme that takes advantage of the extra energy in the system when worst-case scenarios do not happen. Three dynamic policies are shown to make better use of the recharging energy while improving the system value.