A Deadline-Floor Inheritance Protocol for EDF Scheduled Embedded Real-Time Systems with Resource Sharing

Abstract

Earliest Deadline First (EDF) is the most widely studied optimal dynamic scheduling algorithm for uniprocessor real-time systems. For realistic programs, tasks must be allowed to exchange data and use other forms of resources that must be accessed under mutual exclusion. With EDF scheduled systems, access to such resources is usually controlled by the use of Baker's Stack Resource Protocol (SRP). In this paper we propose an alternative scheme based on deadline inheritance. Shared resources are assigned a relative deadline equal to the minimum (floor) of the relative deadlines of all tasks that use the resource. On entry to the resource a task's current absolute deadline is subject to an immediately reduction to reflect the resource's deadline floor. On exit the original deadline for the task is restored. We show that the worst-case behaviour of the new protocol (termed DFP-Deadline Floor inheritance Protocol) is the same as SRP. Indeed it leads to the same blocking term in the scheduling analysis. We argue that the new scheme is however more intuitive, removes the need to support preemption levels and we demonstrate that it can be implemented more efficiently.

Exact comparison of fixed priority and EDF scheduling based on speedup factors for both pre-emptive and non-pre-emptive paradigms

“…We now consider how changes to the task model, allowing tasks to access mutually exclusive shared resources according to the Stack Resource Policy (SRP) (Baker 1991), or to execute critical sections non-preemptively, affect the processor speedup factor required. (We note that the Deadline Floor inheritance Protocol (DFP) (Burns et al 2014) for EDF has the same schedulability conditions as SRP, and hence our results also apply to comparisons between FP+SRP and EDF+DFP).…”

“…(Again, optimality is with respect to a task model where no information is available about the phasing of resource accesses within the tasks). Burns et al (2014) introduced the Deadline Floor inheritance Protocol (DFP), which is equivalent to SRP in terms of schedulability, but has a simpler implementation.…”

“…(ii) The above result holds when tasks may access resources in mutual exclusion according to the Stack Resource Policy (Baker, 1991) (i.e. FP-P +SRP v. EDF-P +SRP) or the Deadline Floor inheritance Protocol (DFP) (Burns et al 2014) (i.e. FP-P +SRP v. EDF-P +DFP).…”

New schedulability analysis for MrsP

“…The Non Preemptive Protocol provides the most straightforward protection to resource-requesting tasks and can be applied with any scheduling scheme. The Priority Inheritance Protocol [24] is 978-1-5386-1898-1/17/ $31.00 c 2017 IEEE suitable for fixed-priority systems and inspired the creation of protocols that are agreed as the best practice for resource sharing control on uniprocessor platforms -Priority Ceiling Protocol (PCP) [24], the Stack Resource Protocol (SRP) [4] and the Deadline Floor Protocol [9]. These protocols guarantee that a task can only suffer from one blocking, as well as avoiding deadlocks and carrying low run-time overheads [14].…”

The Deadline Floor Protocol and Ada

“…Whilst a task accesses a resource its deadline is reduced so that no newly released task can preempt it and then access the resource. See [4,5] for details and proof of the key properties. This is equivalent to the use of a priority ceiling; again the only tasks that can preempt a task executing within a protected object are tasks that are guaranteed not to use that object (unless there is a program error, which can be caught at run-time).…”