Exact Schedulability Test for global-EDF Scheduling of Periodic Hard Real-Time Tasks on Identical Multiprocessors

TL;DR

This paper presents an exact schedulability test for global-EDF scheduling of periodic hard real-time tasks on identical multiprocessors, addressing previous inaccuracies and providing a reliable feasibility interval.

Contribution

It introduces a correct and exact schedulability test for global-EDF on multiprocessors, correcting prior flawed tests and establishing a valid feasibility interval.

Findings

Proves the predictability of global-EDF scheduling.

Provides a correct feasibility interval for schedulability analysis.

Counterexample shows previous tests are incorrect.

Abstract

In this paper we consider the scheduling problem of hard real-time systems composed of periodic constrained-deadline tasks upon identical multiprocessor platforms. We assume that tasks are scheduled by using the global-EDF scheduler. We establish an exact schedulability test for this scheduler by exploiting on the one hand its predictability property and by providing on the other hand a feasibility interval so that if it is possible to find a valid schedule for all the jobs contained in this interval, then the whole system will be stamped feasible. In addition, we show by means of a counterexample that the feasibility interval, and thus the schedulability test, proposed by Leung [Leung 1989] is incorrect and we show which arguments are actually incorrect.