Analysis Techniques for Supporting Harmonic Real-Time Tasks with Suspensions

In many real-time systems, tasks may experience suspension delays when they block to access shared resources or interact with external devices such as I/O. It is known that such suspensions delays may negatively impact schedulability. Particularly in hard real-time systems, a few negative results exist on analyzing the schedulability of such systems, even for very restricted suspending task models on a uniprocessor. In this paper, we focus on the particular case of hard real-time suspending task systems with harmonic periods, which is a special case of practical relevance. We propose a new uniprocessor suspension-aware analysis technique for supporting such task systems under rate-monotonic scheduling. Our analysis technique is able to achieve only Theta(1) suspension-related utilization loss on a uniprocessor. Based upon this technique, we further propose a partitioning scheme that supports suspending task systems with harmonic periods on multiprocessors. The resulting schedulability test shows that compared to existing schedulability tests designed for ordinary non-suspending task systems, suspensions only results in Theta(m) additional suspension-related utilization loss, where m is the number of processors. Furthermore, experiments presented herein show that both our uniprocessor and multiprocessor schedulability tests improve upon prior approaches by a significant margin.