Extended support for limited preemption fixed priority scheduling for OSEK/AUTOSAR-compliant operating systems

Abstract

Fixed Priority Scheduling (FPS) is the de facto standard in industry and it is the scheduling algorithm used in OSEK/AUTOSAR. Applications in such systems are compositions of so-called runnables, the functional entities of the system. Runnables are mapped to operating system tasks during system synthesis. In order to improve system performance it is proposed to execute runnables non-preemptively while varying the tasks threshold between runnables. This allows simpler resource access, which can reduce the stack usage of the system and improve the schedulability of the task sets. FPDS*, as a special case of fixed-priority scheduling with deferred preemptions, executes subjobs non-preemptively and preemption points have preemption thresholds, providing exactly the proposed behavior. However OSEK/AUTOSAR-conform systems cannot execute such schedules. In this paper we present an approach allowing the execution of FPDS* schedules. In our approach we exploit pseudo resources in order to implement FPDS*. It is further shown that our optimal algorithm produces a minimum number of resource accesses. In addition, a simulation-based evaluation is presented in which the number of resource accesses as well as the number of required pseudo-resources by the proposed algorithms are investigated. Finally, we report the overhead of resource access primitives using our measurements performed on an AUTOSAR-compliant operating system.