Reserving Processors by Precise Scheduling of Mixed-Criticality Tasks

Mixed-criticality (MC) scheduling has been proposed to mitigate the pessimism in real-time schedulability analysis that must provide guarantees for the worst case. In most existing work on MC scheduling, low-critical tasks are either dropped or degraded at the criticality mode switch in order to preserve the temporal guarantees for high-critical tasks. Recently, a different direction, called precise MC scheduling, has been investigated. In precise MC scheduling, no low-critical task should be dropped or degraded; instead, the platform processing capacity is augmented at mode switch to accommodate the additional workload by high-critical tasks. In contrast to prior work on this topic with respect to varying processor speed, this work investigates the precise scheduling problem of MC tasks when the number of available processors may vary at the mode switch. To address this new problem, we propose two alternative algorithms by adapting virtual-deadline-based EDF and by fluid scheduling, respectively, and provide a sufficient schedulability test for each. We also conduct schedulability experiments with randomly generated task sets to demonstrate the effectiveness of the proposed algorithms and the benefits of the new scheduling model.