The problem of multiprogram scheduling on a single processor is studied from the viewpoint...

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Increases in processor speeds and the availability of audio and video devices for personal computers have encouraged the development of interactive multimedia applications for teleconferencing and digital audio/video presentation among others. These applications have stringent timing constraints, and traditional operating systems are not well suited to satisfying such constraints. On the other hand, hard real-time systems that can meet these constraints are typically static and inflexible. This dissertation

The problem of preemptive scheduling a set of periodic tasks on multiprocessors is studied from the point of view of meeting their service requirements before their respective deadlines. Sufficient conditions which permit full utilization of the multiprocessor using the given scheduling algorithms are derived. The complexity of the scheduling algorithms in terms of the number of scheduled tasks and the number of processors and upper bounds on the number of preemptions in a given time interval and for any single task are also derived. We also give a schema for modifying existing schedules at little run-time cost when tasks arrive or leave the system on-line.

This paper is concerned with the problem of scheduling preemptive tasks subject to precedence constraints in order to minimize the maximum lateness and the makespan. The number of available parallel processors is allowed to vary in time. It is shown that when an Earliest Due Date first algorithm provides an optimal nonpreemptive schedule for unitexecution -time (UET) tasks, then the preemptive priority scheduling algorithm, referred to as Smallest Laxity First, provides an optimal preemptive schedule for real-execution-time (RET) tasks. When the objective is to minimize the makespan, we get the same kind of result between Highest Level First schedules solving nonpreemptive tasks with UET and the Longest Remaining Path first schedule for the corresponding preemptive scheduling problem with RET tasks. These results are applied to four specific profile scheduling problems and new optimality results are obtained. Keywords: Preemptive Scheduling, List Schedule, Priority Schedule, Variable P...

. Data Flow is a natural paradigm representing distributed programs able to express data and control dependencies between composing nodes. Our work concentrates on periodic Data-Flow programs having Hard Real-Time constraints. We propose a model and a stringbased representation for a relevant class of Data-Flow programs and present a two-phase algorithm able to compute a schedule for a given set of programs to be executed. The first phase computes a feasible solution (mapping and time assignments) using a Simulated Annealing technique, the second phase takes the mapping as input and computes the optimal solution, in terms of resource allocation, using a recursive descent QuasiNewton method. 1 Introduction In this paper we focus on the class of Hard Real-Time (HRT) systems, those which may cause catastrophic effects in case of a timing deadline miss. In HRT program tailored systems, an off-line scheduling analysis [18] is necessary to guarantee the availability of processing resources ...

This paper summarizes a survey of the published research in real-time systems. Material is presented which provides an overview of the topic focusing on communications protocols and scheduling techniques. It is noted that real-time systems deserve special attention separate from other areas because of their unique properties. In computer science and operations research this has not been the case until quite recently resulting in the absence of formal tools for design and analysis of real-time systems. Summaries are given beginning with early work on applications as well as notable theoretical advances. This is followed by descriptions of more recent work in the field from the mid-1980's to the present. Contents 1 Introduction 1 1.1 Real-Time Computer Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 1.2 Real Time LAN Architecture : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 3 2 MAC Layer 4 2.1 Token Ring : : : : : : : : : : : : : : : : : : : :...

: The notion of profile scheduling was first introduced by Ullman in 1975 in the complexity analysis of deterministic scheduling algorithms. In such a model, the number of processors available to a set of tasks may vary in time. Since the last decade, this model has been used to deal with systems subject to processor failures, multiprogrammed systems, or dynamically reconfigured systems. The aim of this paper is to overview optimal polynomial solutions for scheduling a set of partially ordered tasks in these systems. Particular attentions are given to a class of algorithms referred to as list scheduling algorithms. The objective of the scheduling problem is to minimize either the maximum lateness or the makespan. Results on preemptive and nonpreemptive deterministic scheduling, and on preemptive stochastic scheduling, are presented. Keywords: Deterministic Scheduling, Stochastic Scheduling, Profile Scheduling, List Schedule, Priority Schedule, Precedence Constraints, Lateness, Makespan...

In real-time systems, the basic criteria are to satisfy both timeliness and correctness of real-time solutions. The former requirement is controlled by both resource and task scheduling at operating system level whereas the latter is achieved at language level. The efficiency of a scheduling strategy depends upon several factors such as hardware configuration, type of real-time application and the complexity of real-time problem. This report presents a classification of scheduling techniques in order to help designers model their real-time systems with appropriate scheduling schemes to meet their timeliness characteristic. It also aims to explore the scheduling properties and scope of research in real-time computing. 1.0 Introduction In general, real-time systems are classified into soft and hard real-time systems. In soft real-time systems, the tasks are expected to perform as fast as possible. The response time can vary quite considerably, but at the same time can satisfy the deadl...

Abstract Preemptive scheduling problems on parallel machines are classic problems. Given the goal of minimizing the makespan, they are polynomially solvable even for the most general model of unrelated machines. In these problems, a set of jobs is to be assigned to run on a set of m machines. A job can be split into parts arbitrarily and these parts are to be assigned to time slots on the machines without parallelism, that is, for every job, at most one of its parts can be processed at each time. Motivated by sensitivity analysis and online algorithms, we investigate the problem of designing robust algorithms for constructing preemptive schedules. Robust algorithms receive one piece of input at a time. They may change a small portion of the solution as an additional part of the input is revealed. The capacity of change is based on the size of the new piece of input. For scheduling problems, the supremum ratio between the total size of the jobs (or parts of jobs) which may be re-scheduled upon the arrival of a new job j, and the size of j, is called migration factor. We design a strongly optimal algorithm with the migration factor 1 − 1 m for identical machines. Strongly optimal algorithms avoid idle time and create solutions where the (non-increasingly) sorted vector of completion times of the machines is lexicographically minimal. In the case of identical machines this results not only in makespan minimization, but the created solution is also optimal with respect to any ℓp norm (for p>1). We show that an algorithm of a smaller migration factor cannot be optimal with respect to makespan or any other ℓp norm, thus the result is best possible in this sense as well. We further show that neither uniformly related machines