Has energy surpassed timeliness? Scheduling energy-constrained mixed-criticality systems

In the past, we have silently accepted that energy consumption in real-time and embedded systems is subordinate to time. That is, we have tried to reduce energy always under the constraint that all deadlines must be met. In mixed-criticality systems however, schedulers respect that some tasks are more important than others and guarantee their completion even at the expense of others. We believe in these systems the role of the energy budget has changed and it is time to ask whether energy has surpassed timeliness. Investigating energy as a further dimension of mixed-criticality systems, we show in a realistic scenario that a subordinate handling of energy can lead to violations of the mixed-criticality guarantees that can only be avoided if energy becomes an equally important resource as time.