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187
On nonpreemptive scheduling of periodic and sporadic tasks
, 1991
"... Abstract: This paper examines a fundamental problem in the theory of realtime scheduling, that of scheduling a set of periodic or sporadic tasks on a uniprocessor without preemption and without inserted idle time. We exhibit a necessary and sufficient set of conditions C for a set of periodic or sp ..."
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Cited by 165 (9 self)
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Abstract: This paper examines a fundamental problem in the theory of realtime scheduling, that of scheduling a set of periodic or sporadic tasks on a uniprocessor without preemption and without inserted idle time. We exhibit a necessary and sufficient set of conditions C for a set of periodic or sporadic tasks to be schedulable for arbitrary release times of the tasks. We then show that any set of periodic or sporadic tasks that satisfies conditions C can be scheduled with an earliest deadline first (EDF) scheduling algorithm. We also address the question of schedulability of a set of tasks with specified release times. For sets of sporadic tasks with specified release times, we show that the conditions C are again necessary and sufficient for schedulability. However, for sets of periodic tasks with specified release times, the conditions C, while sufficient, are not necessary. In fact, we show that determining whether a set of periodic tasks with specified release times is schedulable is intractable (i.e., NPhard in the strong sense). Moreover, we show that the existence of a universal algorithm for scheduling periodic tasks with specified release times would imply that P = NP. 1.
Multiprocessor EDF and deadline monotonic schedulability analysis
 In Proc. RTSS
, 2003
"... Schedulability tests are presented for preemptive earliestdeadlinefirst and deadlinemonotonic scheduling of periodic or sporadic realtime tasks on a singlequeueserver system, in which the deadline of a task may be less than or equal to the task period. These results subsume and generalize se ..."
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Cited by 107 (6 self)
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Schedulability tests are presented for preemptive earliestdeadlinefirst and deadlinemonotonic scheduling of periodic or sporadic realtime tasks on a singlequeueserver system, in which the deadline of a task may be less than or equal to the task period. These results subsume and generalize several known utilizationbased multiprocessor schedulability tests, and are derived via an independent proof. 1.
New strategies for assigning realtime tasks to multiprocessor systems
 IEEE TRANSACTIONS ON COMPUTERS
, 1995
"... Optimal scheduling of realtime tasks on multiprocessor systems is known to be computationally intractable for large task sets. Any practical scheduling algorithm for assigning realtime tasks to a multiprocessor system presents a tradeoff between its computational complexity and its performance. In ..."
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Cited by 92 (0 self)
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Optimal scheduling of realtime tasks on multiprocessor systems is known to be computationally intractable for large task sets. Any practical scheduling algorithm for assigning realtime tasks to a multiprocessor system presents a tradeoff between its computational complexity and its performance. In this study, new schedulability conditions are presented for homogeneous multiprocessor systems where individual processors execute the ratemonotonic scheduling algorithm. The conditions are used to develop new strategies for assigning realtime tasks to processors. The performance of the new strategies is shown to be significantly better than suggested by the existing literature. Under the realistic assumption that the load of each realtime task is small compared to the processing speed of each processor, it is shown that the processors can be almost fully utilized.
A categorization of realtime multiprocessor scheduling problems and algorithms
 HANDBOOK ON SCHEDULING ALGORITHMS, METHODS, AND MODELS
, 2004
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Adding TimeOffsets to Schedulability Analysis
"... This paper discusses the addition of socalled time offsets to task sets dispatched according to fixed priorities. The motivation for this work is twofold: firstly, direct expression of time offsets is a useful structuring approach for designing complex hard realtime systems. Secondly, analysis di ..."
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Cited by 80 (0 self)
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This paper discusses the addition of socalled time offsets to task sets dispatched according to fixed priorities. The motivation for this work is twofold: firstly, direct expression of time offsets is a useful structuring approach for designing complex hard realtime systems. Secondly, analysis directly addressing time offsets can be very much less pessimistic than extant analysis. In this report we extend our current fixed priority schedulability analysis, and then present two major worked examples, illustrating the approach. 1. INTRODUCTION Previous work has addressed the problem of determining the worstcase timing behaviour of tasks dispatched according to fixed priority scheduling [11, 10]. Much of this work has been aimed at determining the worstcase case response time of a given task; of course, the worstcase response time is, by definition, the response time of the task in the worstcase scheduling scenario. So far, in all these previous pieces of work, tasks have been ass...
A Structured Design Method for Hard Realtime Systems
 RealTime Systems
, 1993
"... Most structured design methods claim to address the needs of hard realtime systems. However, few contain abstractions which directly relate to common hard realtime activities, such as periodic or sporadic processes. Furthermore, the methods do not constrain the designer to produce systems which ca ..."
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Cited by 76 (2 self)
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Most structured design methods claim to address the needs of hard realtime systems. However, few contain abstractions which directly relate to common hard realtime activities, such as periodic or sporadic processes. Furthermore, the methods do not constrain the designer to produce systems which can be analysed for their timing properties. In this paper we present a structured design method called HRTHOOD (Hard RealTime Hierarchical Object Oriented Design). HRTHOOD is an extension of HOOD, and includes object types which enable common hard realtime abstractions to be represented. The method is presented in the context of a hard realtime system life cycle, which enables issues of timeliness and dependability to be addressed much earlier on in the development process. We argue that this will enable dependable realtime systems to be engineered in a more cost effective manner than the current practise, which in effect treats these topics as performance issues. To illustrate our appr...
Worstcase utilization bound for edf scheduling on realtime multiprocessor systems
 In The Proc. of the 12th Euromicro Conference on RealTime Systems (ECRTS
, 2000
"... In this paper we present the utilization bound for Earliest Deadline First (EDF) scheduling on homogeneous multiprocessor systems with partitioning strategies. Assuming that tasks are preemptively scheduled on each processor according to the EDF algorithm, and allocated according to the First Fit ..."
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Cited by 73 (1 self)
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In this paper we present the utilization bound for Earliest Deadline First (EDF) scheduling on homogeneous multiprocessor systems with partitioning strategies. Assuming that tasks are preemptively scheduled on each processor according to the EDF algorithm, and allocated according to the First Fit (FF) heuristic, we prove that the worstcase achievable utilization is 0:5(n + 1), where n is the number of processors. This bound is valid for arbitrary utilization factors. Moreover, if all the tasks have utilization factors under a value , the previous bound is raised, and the new utilization bound considering is calculated. In addition, we prove that no pair of uniprocessor scheduling algorithmallocation algorithm can provide a higher worstcase achievable utilization than that of EDFFF. Finally, simulation provides the averagecase achievable utilization for EDFFF. 1.
OnLine Scheduling on Uniform Multiprocessors
, 2001
"... Each processor in a uniform multiprocessor machine is characterized by a speed or computing capacity, with the interpretation that a job executing on a processor with speed s for t time units completes (s t) units of execution. The online scheduling of hardrealtime systems, in which all jobs mus ..."
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Cited by 61 (10 self)
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Each processor in a uniform multiprocessor machine is characterized by a speed or computing capacity, with the interpretation that a job executing on a processor with speed s for t time units completes (s t) units of execution. The online scheduling of hardrealtime systems, in which all jobs must complete by specified deadlines, on uniform multiprocessor machines is considered. It is known that online algorithms tend to perform very poorly in scheduling such hardrealtime systems on multiprocessors; resourceaugmentation techniques are presented here that permit online algorithms to perform better than may be expected given the inherent limitations. Results derived here are applied to the scheduling of periodic task systems on uniform multiprocessor machines. 1.
Scheduling Hard RealTime Systems: A Review
, 1991
"... Recent results in the application of... this paper. The review takes the form of an analysis of the problems presented by different application requirements and characteristics. Issues covered include uniprocessor and multiprocessor systems, periodic and aperiodic processes, static and dynamic algor ..."
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Cited by 55 (7 self)
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Recent results in the application of... this paper. The review takes the form of an analysis of the problems presented by different application requirements and characteristics. Issues covered include uniprocessor and multiprocessor systems, periodic and aperiodic processes, static and dynamic algorithms, transient overloads and resource usage. Protocols that limit and reduce blocking are discussed. Considerations are also given to scheduling Ada tasks.