Automatic Scheduling of a Dynamic Multimedia Application with POLKA: a Case Study

POLKA is a system to dynamically and automatically schedule application that have temporal QoS constraints. This paper briefly describes the POLKA system and scheduling approach; it then introduces a multimedia application that is used as a case study to show the effectiveness of the approach. The performance measurements presented in the paper were performed on a CORBA based prototype of POLKA. 1 Introduction - Motivation In applications that involve continuous media (e.g. audio and video), information is expressed not only in its individual value, but also by the time of its occurrence. To run smoothly, multimedia applications must therefore meet temporal Quality of Service (QoS) constraints. In order to guaranty that the temporal constraints are met, several proposed multimedia platforms have tempted to use technics derived from the hard real-time field (see [6]). Such technics require a very good knowledge of the application: tasks requirements, in particular in terms of CPU tim..

Optimal priority and threshold assignment for fixed-priority preemption threshold scheduling

Fixed-priority preemption-threshold scheduling (FPTS) is a generalization of fixed-priority preemptive scheduling (FPPS) and fixed-priority non-preemptive scheduling (FPNS). Since FPPS and FPNS are incomparable in terms of potential schedulability, FPTS has the advantage that it can schedule any task set schedulable by FPPS or FPNS and some that are not schedulable by either. FPTS is based on the idea that each task is assigned a priority and a preemption threshold. While tasks are admitted into the system according to their priorities, they can only be preempted by tasks that have priority higher than the preemption threshold. This paper presents a new optimal priority and preemption threshold assignment (OPTA) algorithm for FPTS which in general outperforms the existing algorithms in terms of the size of the explored state-space and the total number of worst case response time calculations performed. The algorithm is based on back-tracking, i.e. it traverses the space of potential priorities and preemption thresholds, while pruning infeasible paths, and returns the first assignment deemed schedulable. We present the evaluation results where we compare the complexity of the new algorithm with the existing one. We show that the new algorithm significantly reduces the time needed to find a solution. Through a comparative evaluation, we show the improvements that can be achieved in terms of schedulability ratio by our OPTA compared to a deadline monotonic priority assignment

Synchronous Modeling and Validation of Priority Inheritance Schedulers,” in Fundamental Approaches to Software Engineering

Abstract. Architecture Description Languages (ADLs) allow embedded systems to be described as assemblies of hardware and software components. It is attractive to use such a global modelling as a basis for early system analysis. However, in such descriptions, the applicative software is often abstracted away, and is supposed to be developed in some host programming language. This forbids to take the applicative software into account in such early validation. To overcome this limitation, a solution consists in translating the ADL description into an executable model, which can be simulated and validated together with the software. In a previous paper [1], we proposed such a translation of Aadl (Architecture Analysis & Design Language) specifications into an executable synchronous model. The present paper is a continuation of this work, and deals with expressing the behavior of complex scheduling policies managing shared resources. We provide a synchronous specification for two shared resource scheduling protocols: the well-known basic priority inheritance protocol (BIP), and the priority ceiling protocol (PCP). This results in an automated translation of Aadl models into a purely Boolean synchronous (Lustre) scheduler, that can be directly model-checked, possibly with the actual software