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  • 1
    Electronic Resource
    Electronic Resource
    Validating Real-Time Constraints in Heterogeneous Multiprocessor and Distributed Systems (1999)
    Springer
    Journal of systems integration 9 (1999), S. 207-222 
    Details
    ISSN: 1573-8787
    Keywords: Validation ; Schedulability Analysis ; Distributed Real-Time Systems ; Heterogeneous Systems ; Dynamic Systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract A heterogeneous system or distributed system typically contains different types of processors. Some jobs can execute on certain types of processors but not other types. Processors of different types may have different speeds. We present several worst-case upper bounds and efficient algorithms for determining the completion times of independent jobs that have arbitrary timing constraints and variable execution times and are scheduled on available processors dynamically in a priority-driven manner. Bounds and algorithms take into account the effects of nonmigratability, nonpreemptability and different levels of migratability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026436324575
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Algorithms and optimality of scheduling soft aperiodic requests in fixed-priority preemptive systems (1996)
    Springer
    Real-time systems 10 (1996), S. 23-43 
    Details
    ISSN: 1573-1383
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this paper, we investigate the problem of scheduling soft aperiodic requests in systems where periodic tasks are scheduled on a fixed-priority, preemptive basis. First, we show that given any queueing discipline for the aperiodic requests, no scheduling algorithm can minimize the response time of every aperiodic request and guarantee that the deadlines of the periodic tasks are met when the periodic tasks are scheduled on a fixed-priority, preemptive basis. We then develop two algorithms: Algorithm $$\mathcal{L}$$ is locally optimal in that it minimizes the response time of the aperiodic request at the head of the aperiodic service queue. Algorithm $$\mathcal{G}$$ is globally optimal in that it completes the current backlog of work in the aperiodic service queue as early as possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357882
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    An Open Environment for Real-Time Applications (1999)
    Springer
    Real-time systems 16 (1999), S. 155-185 
    Details
    ISSN: 1573-1383
    Keywords: open-system ; real-time application ; two-level scheduler
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper describes an open system architecture that allows independently developed hard real-time applications to run together and supports their reconfiguration at run-time. In the open system, each real-time application is executed by a server. At the lower level, the OS scheduler schedules all the servers on the EDF basis. At the upper level, the server scheduler of each server schedules the ready jobs of the application executed by the server according to the algorithm chosen for the application. The paper describes the two-level CPU scheduling scheme used by the open system and the design and implementation of a uniprocessor open system within the framework of the Windows NT operating system. The implementation consists of three key components: the two-level hierarchical kernel scheduler, common system service providers, and real-time application programming interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008094905565
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Performance analysis of multiprocessor systems containing functionally dedicated processors (1978)
    Springer
    Acta informatica 10 (1978), S. 95-104 
    Details
    ISSN: 1432-0525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Summary General models of multiprocessor systems in which processors are functionally dedicated are described. In these models, processors are divided into different types. A task can be assigned only to a processor of certain types. Clearly, the model of multiprocessor systems with identical processors is a special case of our models. These models also include the job shop problem in which there is exactly one processor of each type. Worst case performance bounds of priority-driven schedules are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00260927
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  • 5
    Electronic Resource
    Electronic Resource
    Greed in resource scheduling (1991)
    Springer
    Acta informatica 28 (1991), S. 755-775 
    Details
    ISSN: 1432-0525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We examine the worst-case performance of a class of heuristic scheduling algorithms commonly referred to as priority-driven or list-scheduling algorithms. It is well known that these algorithms have anomalous, unpredictable performance when used to schedule nonpreemptive tasks with precedence constraints. We present a general method for deriving the worst-case performance of these algorithms. This method is easy to use, yet powerful enough to yield tight performance bounds for many classes of scheduling problems. We demonstrate the method for several problems to show it has wide applicability. We also present several task systems for which list-scheduling algorithms exhibit unavoidable worst-case performance and discuss the general characteristics of these task systems. These task systems are sometimes overlooked in simulation studies; consequently, the results of these studies may be overly optimistic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01261655
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Scheduling with slack time (1982)
    Springer
    Acta informatica 17 (1982), S. 31-41 
    Details
    ISSN: 1432-0525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Summary We consider a scheduling problem concerning a set of jobs {J 1, J 2,..., J n } in which the job J i requests C i units of computation time every T i units of time periodically. These jobs are to be executed by a timeshared single-processor computing system. It is assumed that the requests for each job arrive at the system at the beginning of the request periods and that deadline for completion of the requested computation in each period coincides with the beginning of the next period. For a set of jobs that is schedulable by a certain algorithm, the time span between the completion of a request and its deadline is referred to as the slack time of the request. It is shown here that when the set of jobs is scheduled according to the rate monotonic algorithm, the slack time of the first request of any job is no larger than the slack time of any subsequent request of that job. This result enables us to determine lower bounds to slack times of all requests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262974
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    Paper (German National Licenses)
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  • 7
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    Imprecise results: Utilizing partial computations in real-time systems (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: In real-time systems, a computation may not have time to complete its execution because of deadline requirements. In such cases, no result except the approximate results produced by the computations up to that point will be available. It is desirable to utilize these imprecise results if possible. Two approaches are proposed to enable computations to return imprecise results when executions cannot be completed normally. The milestone approach records results periodically, and if a deadline is reached, returns the last recorded result. The sieve approach demarcates sections of code which can be skipped if the time available is insufficient. By using these approaches, the system is able to produce imprecise results when deadlines are reached. The design of the Concord project is described which supports imprecise computations using these techniques. Also presented is a general model of imprecise computations using these techniques, as well as one which takes into account the influence of the environment, showing where the latter approach fits into this model.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-180561 , NAS 1.26:180561
    Format: application/pdf
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  • 8
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    Scheduling real-time, periodic jobs using imprecise results (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A process is called a monotone process if the accuracy of its intermediate results is non-decreasing as more time is spent to obtain the result. The result produced by a monotone process upon its normal termination is the desired result; the error in this result is zero. External events such as timeouts or crashes may cause the process to terminate prematurely. If the intermediate result produced by the process upon its premature termination is saved and made available, the application may still find the result unusable and, hence, acceptable; such a result is said to be an imprecise one. The error in an imprecise result is nonzero. The problem of scheduling periodic jobs to meet deadlines on a system that provides the necessary programming language primitives and run-time support for processes to return imprecise results is discussed. This problem differs from the traditional scheduling problems since the scheduler may choose to terminate a task before it is completed, causing it to produce an acceptable but imprecise result. Consequently, the amounts of processor time assigned to tasks in a valid schedule can be less than the amounts of time required to complete the tasks. A meaningful formulation of this problem taking into account the quality of the overall result is discussed. Three algorithms for scheduling jobs for which the effects of errors in results produced in different periods are not cumulative are described, and their relative merits are evaluated.
    Keywords: ADMINISTRATION AND MANAGEMENT
    Type: NASA-CR-180562 , NAS 1.26:180562
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Producing approximate answers to database queries (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We have designed and implemented a query processor, called APPROXIMATE, that makes approximate answers available if part of the database is unavailable or if there is not enough time to produce an exact answer. The accuracy of the approximate answers produced improves monotonically with the amount of data retrieved to produce the result. The exact answer is produced if all of the needed data are available and query processing is allowed to continue until completion. The monotone query processing algorithm of APPROXIMATE works within the standard relational algebra framework and can be implemented on a relational database system with little change to the relational architecture. We describe here the approximation semantics of APPROXIMATE that serves as the basis for meaningful approximations of both set-valued and single-valued queries. We show how APPROXIMATE is implemented to make effective use of semantic information, provided by an object-oriented view of the database, and describe the additional overhead required by APPROXIMATE.
    Keywords: DOCUMENTATION AND INFORMATION SCIENCE
    Type: NASA. Lyndon B. Johnson Space Center, The Sixth Annual Workshop on Space Operations Applications and Research (SOAR 1992); p 398-405
    Format: application/pdf
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  • 10
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    PERTS: A Prototyping Environment for Real-Time Systems (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: PERTS is a prototyping environment for real-time systems. It is being built incrementally and will contain basic building blocks of operating systems for time-critical applications, tools, and performance models for the analysis, evaluation and measurement of real-time systems and a simulation/emulation environment. It is designed to support the use and evaluation of new design approaches, experimentations with alternative system building blocks, and the analysis and performance profiling of prototype real-time systems.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA. Lyndon B. Johnson Space Center, The Sixth Annual Workshop on Space Operations Applications and Research (SOAR 1992); p 372-379
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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