Rate Monotonic Priority Assignment Research Articles

Real‐time scheduling of multiple uncertain receding horizon control systems

AbstractIn this paper, a new scheduling approach is proposed that considers the effect of modeling uncertainty for multiple continuous time receding horizon control (RHC) systems. This is accomplished by combining a scheduling approach with results from the continuous time nonlinear systems theory. It is shown that using a rate monotonic priority assignment method combined with analytical bounds on the prediction error, the problem of scheduling multiple uncertain plants can be cast into an appropriate constrained optimization problem. The constraints guarantee that the processes will be schedulable. The optimization provides optimized performance and balanced resource allocation in the presence of uncertainty. The proposed method was applied to a real‐time simulation of RHC trajectory tracking for two hovercraft vehicles demonstrating the validity of the approach. Copyright © 2008 John Wiley & Sons, Ltd.

An Improved Rate Monotonic Schedulability Test Algorithm

One of the key issues in real-time theory is the schedulable analysis of a given task set with fixed priority. All the proposed schedulability test methods can be classified into two types: polynomial time methods and exact methods. Polynomial time methods use a sufficient schedulability condition, and several least upper bounds of the processor utilization under ideal assumptions have been developed. Exact methods based on the necessary and sufficient schedulability condition guarantee that the test result for every task set is correct. However, the pseudo-polynomial complexity of the exact tests is too complex to be executed online for large task sets. This paper presents a novel ISTA (improved schedulability test algorithm) for analyzing the schedulability of periodic task sets under Rate Monotonic priority assignment. A pruning theorem for the Task_i space is derived, the schedulability correlation among tasks and its effect on the schedulability test are investigated, and the related theorems are proven. Based on the above results, a new improved pseudo-polynomial schedulability test algorithm is developed, and several comparative simulation experiments among the three methods are conducted. Extensive simulations show that the average schedulability test performance as a function of number of the tasks can be significantly improved.

Deadline monotonic scheduling theory and application

Scheduling theories are now sufficiently mature that a genuine engineering approach to the construction of hard real-time systems is possible. In this paper we discuss the application of Deadline Monotonic Scheduling Theory (DMST). This theory is an extension of the more familiar approach based on rate monotonic priority assignment. The model presented can accomodate periodic and sporadic processes, different levels of criticality, process interaction and blocking, precedence constrained processes and multi-deadline processes. It is particularly well integrated with the use of Immediate Priority Ceiling Inheritance for control over process blocking. A basic pseudo-polynomial schedulability test is outlined and then supplemented by the introduction of offsets to control jitter, and period transformation to enable critical (hard) processes to be “protected” during potential transient overloads. These mathematical techniques derived within DMST can help designers experiment with alternative formulations and prove essential properties of systems before they are deployed.