Scheduling Periodic Segmented Self-Suspending Tasks without Timing Anomalies

Timing guarantee is an important aspect and must be ensured for every individual task in real-time systems. Even for periodic tasks, providing timing guarantees for segmented self-suspending tasks is challenging due to timing anomalies, i.e., the reduction of execution or suspension time of some jobs enlarges the response time of another job. The existing worst-case response time analyses for sporadic self-suspending tasks are only over-approximations and lead to overly pessimistic results. In this paper, we focus on eliminating timing anomalies without negative impacts on the worst-case response time (WCRT) analysis when scheduling periodic tasks with segmented self-suspension behavior. We propose two treatments, segment release time enforcement and segment priority modification, and prove that both treatments eliminate timing anomalies. In our evaluation, the proposed treatments achieve higher acceptance ratios in terms of schedulability compared to state-of-the-art scheduling algorithms. We also implement the segment-level fixed-priority scheduling mechanism on RTEMS, and showcase the validity of the treatment segment priority modification.