This paper focuses on the problem of providing efficient run-time support to multimedia applications in a real-time system, where two types of tasks can coexist simultaneously: multimedia soft real-time tasks and hard real-time tasks. Hard tasks are guaranteed based on worst case execution times and minimum interarrival times, whereas multimedia and soft tasks are served based on mean parameters. The paper describes a server-based mechanism for scheduling soft and multimedia tasks without jeopardizing the a priori guarantee of hard real-time activities. The performance of the proposed method is compared with that of similar service mechanisms through extensive simulation experiments and several multimedia applications have been implemented on the HARTIK kernel.

This paper focuses on the problem of providing run-time support to real-time applications and non-real-time applications in an open system environment. It extends the two-level hierarchical scheduling scheme in [12] for scheduling independently developed applications. The extended scheme removes the following two restrictive requirements of the scheme in [12]: (1) real-time applications that are scheduled preemptively must consist solely of periodic tasks, and (2) applications must not share global resources (i.e., resources used by more than one applications). Consequently, the extended scheme allows us to deal with a much broader range of real-time applications. 1 Introduction Recent advances in real-time systems technology have given us many good schemes for scheduling hard real-time applications. Examples are [1, 2, 5, 8]. A weakness shared by most existing schemes is that schedulability analysis must be done globally (i.e., by analyzing all applications in the system together) in...

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An increasing number of real-time applications, related to multimedia and adaptive control systems, require greater flexibility than classical real-time theory usually permits. In this paper we present a novel periodic task model, in which tasks' periods are treated as springs, with given elastic coefficients. Under this framework, periodic tasks can intentionally change their execution rate to provide different quality of service, and the other tasks can automatically adapt their periods to keep the system underloaded. The proposed model can also be used to handle overload conditions in a more flexible way, and provide a simple and efficient mechanism for controlling the quality of service of the system as a function of the current load.

Hierarchical CPU scheduling has emerged as a way to (1) support applications with diverse scheduling requirements in open systems, and (2) provide load isolation between applications, users, and other resource principals. Most existing work on hierarchical scheduling has focused on systems that provide a fixed scheduling model: the schedulers in part or all of the hierarchy are specified in advance. In this paper we describe a system of guarantees that permits a general hierarchy of soft real-time schedulers—one that contains arbitrary scheduling algorithms at all points within the hierarchy—to be analyzed. This analysis results in deterministic guarantees for threads at the leaves of the hierarchy. We also describe the design, implementation, and performance evaluation of a system for supporting such a hierarchy in the Windows 2000 kernel. Finally, we show that complex scheduling behaviors can be created using small schedulers as components and describe the HLS programming environment. 1.

Dynamic voltage scaling (DVS), which adjusts the clock speed and supply voltage dynamically, is an effective technique in reducing the energy consumption of embedded realtime systems. The energy efficiency of a DVS algorithm largely depends on the performance of the slack estimation method used in it. In this paper, we propose a novel DVS algorithm for periodic hard real-time tasks based on an improved slack estimation algorithm. Unlike the existing techniques, the proposed method takes full advantage of the periodic characteristics of the real-time tasks under priority-driven scheduling such as EDF. Experimental results show that the proposed algorithm reduces the energy consumption by 20#40% over the existing DVS algorithm. The experiment results also show that our algorithm based on the improved slack estimation method gives comparable energy savings to the DVS algorithm based on the theoretically optimal (but impractical) slack estimation method.

When executing different real-time applications on a single processor system, one problem is how to compose these applications and guarantee at the same time that their timing requirements are not violated. A possible way of composing applications is through the resource reservation approach. Each application is handled by a dedicated server that is assigned a fraction of the processor. Using this approach, the system can be seen as a two-level hierarchical scheduler. A considerable amount of work has been recently addressed to the analysis of this kind of hierarchical systems. However, a question is still unanswered: given a set of real-time tasks to be handled by a server, how to assign the server parameters so that the task set is feasible? In this paper, we answer to the previous question for the case of fixed priority local scheduler by presenting a methodology for computing the class of server parameters that make the task set feasible.

When hard periodic and f&-m aperiodic tasks are jointly scheduled in the same system, the processor workload can vary according to the arrival times of aperiodic requests. In order to guarantee the schedu-lability of the periodic task set, in overload conditions some aperiodic tasks must be rejected. In this paper we propose a technique that, in over-load conditions, adds robustness to the joint schedul-ing of periodic and aperiodic tasks in systems with dy-namic priorities. Our technique is based on an ape-riodic server, called Total Bandwidth server, already proven effective in a previous work. Here the algo-rithm is first extended to eficiently h,andle firm aperi-odic tasks and then integrated with a robust guarantee mechanism that allows to achieve graceful degradation in case of transient overloads. Extensive simulations show that the proposed new algorithm is effective in all workload conditions. 1

AbstractÐAn increasing number of real-time applications, related to multimedia and adaptive control systems, require greater flexibility than classical real-time theory usually permits. In this paper, we present a novel scheduling framework in which tasks are treated as springs with given elastic coefficients to better conform to the actual load conditions. Under this model, periodic tasks can intentionally change their execution rate to provide different quality of service and the other tasks can automatically adapt their periods to keep the system underloaded. The proposed model can also be used to handle overload conditions in a more flexible way and to provide a simple and efficient mechanism for controlling a system's performance as a function of the current load. Index TermsÐReal-time scheduling, overload management, rate adaptation. 1

This paper focuses on the problem of providing runtime support to real-time applications and non-real-time applications in an open system. It describes a two-level hierarchical priority-driven scheme for scheduling independently developed applications. The scheme allows the developer of each real-time application to validate the schedulability of the application independently of other applications. Once areal-time application is created and accepted by the open system, its schedulability is guaranteed regardless of the behaviors of other applications that execute concurrently in the system.