Abstract
A challenge in the design of cyber-physical systems is to integrate the scheduling of tasks of different criticality, while still providing service guarantees for the higher critical tasks in the case of resource-shortages caused by faults. While standard real-time scheduling is agnostic to the criticality of tasks, the scheduling of tasks with different criticalities is called mixed-criticality scheduling. In this paper, we present the Lazy Bailout Protocol (LBP), a mixed-criticality scheduling method where low-criticality jobs overrunning their time budget cannot threaten the timeliness of high-criticality jobs while at the same time the method tries to complete as many low-criticality jobs as possible. The key principle of LBP is instead of immediately abandoning low-criticality jobs when a high-criticality job overruns its optimistic WCET estimate, to put them in a low-priority queue for later execution. To compare mixed-criticality scheduling methods, we introduce a formal quality criterion for mixed-criticality scheduling, which, above all else, compares schedulability of high-criticality jobs and only afterwards the schedulability of low-criticality jobs. Based on this criterion, we prove that LBP behaves better than the original Bailout Protocol (BP). We show that LBP can be further improved by slack time exploitation and by gain time collection at runtime, resulting in LBPSG. We also show that these improvements of LBP perform better than the analogous improvements based on BP.
Highlights
Cyber-physical systems (CPS) typically require the integration of services of different criticality.At the same time, it is important that tasks of lower criticality have limited leverage to influence the schedulability of tasks with higher criticality in the case of resource shortages
The only difference between Bailout Protocol (BP) and Lazy Bailout Protocol (LBP) lies in the handling of LO jobs, where LBP puts them in a lower priority scheduling queue instead of abandoning them immediately when released in Bailout/Recovery modes or dropping them after the overrun of their CLO as BP does
Part 1: The strength of Bailout Protocol-Slack (BPS) over BP consists of the scaling up of the optimistic worst-case execution time (WCET) of HI tasks to increase the duration of Normal mode and to decrease the amount of time the system runs in Bailout mode
Summary
Cyber-physical systems (CPS) typically require the integration of services of different criticality. Traditional real-time scheduling protocols, such as rate-monotonic scheduling (RMS) or earliest deadline first (EDF) [1], give priority to jobs with the most strict timing requirements. This approach works well as long as it can be assured that enough resources are available to schedule all tasks. The basic idea of mixed-criticality scheduling protocols is that, as long as enough resources are available, the scheduling priorities are defined by a real-time scheduling protocol. A formal criterion to compare different mixed-criticality scheduling protocols with priority given to high-criticality jobs is defined. We present a new mixed-critcality approach named LBP in Section 4 that does not suddenly abandon LO task instances during resource shortages.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
