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The NPcompleteness column: an ongoing guide
 Journal of Algorithms
, 1985
"... This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NPcompleteness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NPCompleteness,’ ’ W. H. Freeman & Co ..."
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Cited by 188 (0 self)
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This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NPcompleteness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NPCompleteness,’ ’ W. H. Freeman & Co., New York, 1979 (hereinafter referred to as ‘‘[G&J]’’; previous columns will be referred to by their dates). A background equivalent to that provided by [G&J] is assumed, and, when appropriate, crossreferences will be given to that book and the list of problems (NPcomplete and harder) presented there. Readers who have results they would like mentioned (NPhardness, PSPACEhardness, polynomialtimesolvability, etc.) or open problems they would like publicized, should
Scheduling Dependent RealTime Activities
, 1990
"... A realtime application is typically composed of a number of cooperating activities that must execute within specific time intervals. Since there are usually more activities to be executed than there are processors on which to execute them, several activities must share a single processor. Necessari ..."
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Cited by 74 (1 self)
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A realtime application is typically composed of a number of cooperating activities that must execute within specific time intervals. Since there are usually more activities to be executed than there are processors on which to execute them, several activities must share a single processor. Necessarily, satisfying the activities' timing constraints is a prime concern in making the scheduling decisions for that processor.
On realtime databases: Concurrency control and scheduling
 Proceedings of the IEEE
, 1994
"... In addition to maintaining database consistency as in conventional databases, realtime database systems must also handle transactions with timing constraints. While transaction response time and throughput are usually used to measure a conventional database system, the percentage of transactions sa ..."
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Cited by 59 (9 self)
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In addition to maintaining database consistency as in conventional databases, realtime database systems must also handle transactions with timing constraints. While transaction response time and throughput are usually used to measure a conventional database system, the percentage of transactions satisfying the deadlines or a timecritical value function is often used to evaluate a realtime database system. Scheduling realtime transactions is far more complex than traditional realtime scheduling in the sense that (1) worstcase execution times are typically hard to estimate, since not only CPU but also I/O requirement isinvolved � and (2) certain aspects of concurrency control may not integrate well with realtime scheduling. In this paper, we rst develop a taxonomy of the underlying design space of concurrency control including the various techniques for achieving serializability and improving performance. This taxonomy provides us with a foundation for addressing the realtime issues. We then consider the integration of concurrency control with realtime requirements. The implications of using run policies to better utilize realtime scheduling in a database environment are examined. Finally, as timing constraints may be more important than data consistency in certain hard realtime database applications, we also discuss several approaches that explore the nonserializable semantics of realtime transactions to meet the hard deadlines. Index terms: concurrency control, realtime databases, realtime scheduling, realtime transactions, serializability, schedulability.
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 48 (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.
RealTime System Scheduling
, 1990
"... Recent results in the application of scheduling theory to dependable realtime systems are reviewed. 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 ..."
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Cited by 19 (0 self)
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Recent results in the application of scheduling theory to dependable realtime systems are reviewed. 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 bound and reduce blocking are discussed. A review of specific realtime kernels is also included.
Operating System Resource Reservation for RealTime and Multimedia Applications
, 1997
"... 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, an ..."
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Cited by 10 (0 self)
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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 realtime systems that can meet these constraints are typically static and inflexible. This dissertation
Is A UnitTime Job Shop Not Easier Than Identical Parallel Machines?
 Discrete Appl. Math
, 1998
"... . This paper gives the positive answer to the question posed in the title for a wide class of minimization criteria including the maximum completion time, maximum lateness, total completion time, total weighted completion time, total tardiness, total weighted tardiness, number of late jobs and th ..."
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Cited by 8 (7 self)
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. This paper gives the positive answer to the question posed in the title for a wide class of minimization criteria including the maximum completion time, maximum lateness, total completion time, total weighted completion time, total tardiness, total weighted tardiness, number of late jobs and the weighted number of late jobs. That is any scheduling problem for m identical parallel machines to minimize a criterion of the class reduces to a scheduling problem for an mmachine unittime job shop to minimize the same criterion. Employing this general reduction we prove the NPhardness of unittime jobshop scheduling problems which had unknown complexity status before. The paper also presents a comprehensive picture of complexity results attained in unittime jobshop scheduling and related open problems. Introduction Jobshop scheduling and identicalparallelmachines scheduling to minimize a criterion are problems with dierent types of the machine environment. In the former p...
Network Flow Techniques for Dynamic Voltage Scaling in Hard RealTime Systems
 IEEE Transactions on ComputerAided Design of Integrated Circuits and Systems
, 2004
"... Energy consumption is an important performance parameter for portable and wireless embedded systems. However, energy consumption must be carefully balanced with realtime responsiveness in hard realtime systems. In this paper, we present two offline dynamic voltage scaling (DVS) schemes for dynamic ..."
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Cited by 7 (0 self)
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Energy consumption is an important performance parameter for portable and wireless embedded systems. However, energy consumption must be carefully balanced with realtime responsiveness in hard realtime systems. In this paper, we present two offline dynamic voltage scaling (DVS) schemes for dynamic power management in such systems. In the first method, we develop a generalized network flow (GNF) model for the uniprocessor DVS problem and solve it optimally using an efficient network flow algorithm. The proposed method outperforms existing DVS schemes for several popular embedded processors where the number of processor speeds is limited to a few values. The solutions for the GNF model provide theoretical lower bounds on energy consumption using DVS in hard realtime systems. We also describe a minimumcost network flow model whose solutions are nearoptimal. The minimumcost models perform at par with competing methods for processor models with a large range of operating voltages, and better than them for processor models with a limited set of operating voltages.
An Optimal Multiprocessor RealTime Scheduling Algorithm
 Journal of Parallel and Distributed Computing
, 1997
"... An optimal scheduling algorithm is described that feasibly schedules a set of m periodic tasks on n processors before their respective deadlines, if the task set satisfies certain conditions. The complexity of this scheduling algorithm in terms of the number of scheduled tasks and the number of p ..."
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Cited by 7 (0 self)
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An optimal scheduling algorithm is described that feasibly schedules a set of m periodic tasks on n processors before their respective deadlines, if the task set satisfies certain conditions. The complexity of this scheduling algorithm 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 is also derived. The optimal algorithm is shown to be particularly useful when schedules are built from the integral flow values obtained from the corresponding maximum flow network. 1 Introduction Hard realtime systems are those systems [St88] in which the correctness of the system depends not only on the logical result of computation, but also on the time at which the results are produced. Severe consequences will result if timing correctness properties of the system are violated. Applications of realtime systems can be found in automated factories, robot and vision systems, mili...
Multiprocessors Scheduling for Imprecise Computations in a Hard RealTime Environment
 Proc. IEEE RTS
, 1993
"... This paper discusses the problem of scheduling multiprocessors in a hard realtime environment allowing imprecise computations. When results of the desired quality cannot be produced in time, then intermediate, imprecise results of acceptable quality are accepted. In an imprecise computation model, ..."
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Cited by 2 (0 self)
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This paper discusses the problem of scheduling multiprocessors in a hard realtime environment allowing imprecise computations. When results of the desired quality cannot be produced in time, then intermediate, imprecise results of acceptable quality are accepted. In an imprecise computation model, a task may be terminated any time after it has produced an acceptable result. Such tasks are logically decomposed into two parts: the mandatory part followed by an optional part. In a feasible schedule, the mandatory part of every task is completed before the deadline of the task. The optional part refines the result produced by the mandatory part to reduce the error in the result. The optional parts need not ever be completed. The quality of the result of each job is measured in terms of the average error in the results over several consecutive periods. So given n realtime periodic jobs which has a periodicity and a processing requirement per period, the problem of determining whether ther...