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Showing papers on "Scheduling (computing) published in 1985"


Journal ArticleDOI
Yung-Terng Wang1, Morris2
TL;DR: A taxonomy of load sharing algorithms is proposed that draws a basic dichotomy between source- initiative and server-initiative approaches and a performance metric called the Q-factor (quality of load share) is defined which summarizes both overall efficiency and fairness of an algorithm.
Abstract: An important part of a distributed system design is the choice of a load sharing or global scheduling strategy. A comprehensive literature survey on this topic is presented. We propose a taxonomy of load sharing algorithms that draws a basic dichotomy between source-initiative and server-initiative approaches. The taxonomy enables ten representative algorithms to be selected for performance evaluation. A performance metric called the Q-factor (quality of load sharing) is defined which summarizes both overall efficiency and fairness of an algorithm and allows algorithms to be ranked by performance. We then evaluate the algorithms using both mathematical and simulation techniques. The results of the study show that: i) the choice of load sharing algorithm is a critical design decision; ii) for the same level of scheduling information exchange, server-initiative has the potential of outperforming source-initiative algorithms (whether this potential is realized depends on factors such as communication overhead); iii) the Q-factor is a useful yardstick; iv) some algorithms, which have previously received little attention, e.g., multiserver cyclic service, may provide effective solutions.

507 citations


Journal ArticleDOI
Robert J. Wittrock1
TL;DR: This paper discusses scheduling algorithms for a certain kind of manufacturing environment, called the “flexible flow line,” and new heuristic algorithms specially suited to solve these problems in the context of a flexible flow line.
Abstract: This paper discusses scheduling algorithms for a certain kind of manufacturing environment, called the “flexible flow line.” Two scheduling problems are considered. “Loading” decides when each part should be loaded into the system. “Mix allocation” selects the daily part mix. The goals are to maximize throughput and reduce WIP. New heuristic algorithms specially suited to solve these problems in the context of a flexible flow line are described. The paper also discusses experience with the use of an experimental implementation of these algorithms to solve such problems arising in a real production line.

192 citations


Journal ArticleDOI
TL;DR: This work identifies polynomial time solvable special cases and derive good performance bounds for several natural approximation algorithms, assuming the existence of a central controller, and shows how these bounds can be maintained in a distributed regime.
Abstract: We consider a problem of scheduling file transfers in a network so as to minimize overall finishing time. Although the general problem is NP-complete, we identify polynomial time solvable special cases and derive good performance bounds for several natural approximation algorithms, assuming the existence of a central controller. We also show how these bounds can be maintained in a distributed regime.

183 citations


Journal ArticleDOI
TL;DR: The authors present a scheduling algorithm which works dynamically and on loosely coupled distributed systems for tasks with hard real-time constraints; i.e., the tasks must meet their deadlines.
Abstract: Most systems which are required to operate under severe real-time constraints assume that all tasks and their characteristics are known a priori. Scheduling of such tasks can be done statistically. Further, scheduling algorithms operating under such conditions are usually limited to multiprocessor configurations. The authors present a scheduling algorithm which works dynamically and on loosely coupled distributed systems for tasks with hard real-time constraints; i.e., the tasks must meet their deadlines. It uses a scheduling component local to every node and a distributed scheduling scheme which is specifically suited to hard real-time constraints and other timing considerations. Periodic tasks, nonperiodic tasks, scheduling overheads, communication overheads due to scheduling and preemption are all accounted for in the algorithm. Simulation studies are used to evaluate the performance of the algorithm.

180 citations


Journal ArticleDOI
TL;DR: A heuristic routing and scheduling algorithm is shown to produce high quality solutions in reasonable computation time by testing on moderately sized real data bases from both Gaithers-burg, Maryland, and Baltimore, Maryland.
Abstract: A set of n customers is given. Each customer has a desired point of pickup, a desired point of delivery and a desired time of delivery. The problem is to determine the order of pickup and delivery and the times of pickup and delivery of these n customers by a single vehicle in order to minimize total customer inconvenience. Here, a mathematical programming formulating of this problem is subjected to Benders' decomposition procedure. The result is a heuristic routing and scheduling algorithm which is shown to produce high quality solutions in reasonable computation time by testing on moderately sized real data bases from both Gaithers-burg, Maryland, and Baltimore, Maryland. This study is divided into two parts, the first detailing the scheduling analysis and the second focusing on the routing component.

179 citations


Patent
15 Mar 1985
TL;DR: A task scheduler utilizes a combination of externally assigned priorities and internally calculated priorities to optimize the responsiveness of the computer to external interactions as mentioned in this paper. But, task schedulers do not have the ability to schedule the execution of a plurality of tasks within a computer system.
Abstract: A task schedular for scheduling the execution of a plurality of tasks within a computer system. The task scheduler utilizes a combination of externally assigned priorities and internally calculated priorities to optimize the responsiveness of the computer to external interactions.

132 citations


Journal ArticleDOI
TL;DR: A heuristic for the effective cooperation of multiple decentralized components of a job scheduling function that can dynamically adapt to the quality of the state information being processed and is based on Bayesian decision theory.
Abstract: There is a wide spectrum of techniques that can be aptly named decentralized control. However, certain functions in distributed operating systems, e.g., scheduling, operate under such demanding requirements that no known optimal control solutions exist. It has been shown that heuristics are necessary. This paper presents a heuristic for the effective cooperation of multiple decentralized components of a job scheduling function. An especially useful feature of the heuristic is that it can dynamically adapt to the quality of the state information being processed. Extensive simulation results show the utility of this heuristic. The simulation results are compared to several analytical models and a baseline simulation model. The heuristic itself is based on the application of Bayesian decision theory. Bayesian decision theory was used because its principles can be applied as a systematic approach to complex decision making under conditions of imperfect knowledge, and it can run relatively cheaply in real time.

123 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a new algorithm to find the optimal unit commitment and economic dispatch (UC/D) for a large hydrothermal power system, which is a large nonlinear, mixed integer optimization problem involving over 16,800 integer variables.
Abstract: In this paper we present a new algorithm to find the optimal unit commitment and economic dispatch (UC/D) for a large hydrothermal power system. Mathematically, this is a large nonlinear, mixed integer optimization problem involving over 16,800 integer variables for a system having 100 thermal units with a 1-week scheduling horizon. We use a dual programming approach to solve a separate optimal control problem for each thermal unit and for each set of coupled hydro units. The algorithm has been tested on a 100 thermal unit/6 hydro unit system having a 168-hour scheduling period, and will find solutions that are within 0.1 to 0.25 percent of the optimal dual cost. We report computational results for a system modeled after the New York Power Pool.

108 citations


Book
01 Jan 1985
TL;DR: In this paper, the authors present a computer scheduling of public transport in the context of public transportation systems, which is based on the idea of public-transit scheduling of buses.
Abstract: (1986). Computer Scheduling of Public Transport 2. Journal of the Operational Research Society: Vol. 37, No. 6, pp. 649-649.

101 citations


Journal ArticleDOI
TL;DR: Two very different distributed scheduling algorithms which contain explicit mechanisms for stability are presented and evaluated and indicate how very specific the treatment of stability is to the algorithm and environnent under consideration.
Abstract: Many distributed scheduling algorithms have been developed and reported in the current literature. However, very few of them explicitly treat stability issues. This paper first discusses stability issues for distributed scheduling algorithms in general terms. Two very different distributed scheduling algorithms which contain explicit mechanisms for stability are then presented and evaluated with respect to individual specific stability issues. One of the agorithms is based on stochastic learning automata and the other on bidding. The results indicate how very specific the treatment of stability is to the algorithm and environnent under consideration.

85 citations


Journal ArticleDOI
TL;DR: A family of algorithms is described for finding optimum schedules for job-shops that are of a branch and bound type but have a complete schedule associated with each node of the search tree.
Abstract: A family of algorithms is described for finding optimum schedules for job-shops. The algorithms are of a branch and bound type but have a complete schedule associated with each node of the search tree. Branching from nodes is based on important conflicts in the schedule. Some results are provided.

Journal ArticleDOI
TL;DR: A new methodology for performance analysis of flexible manufacturing systems (FMSs) with priority scheduling is presented, and extensive numerical calculations have shown that the algorithm used for solving the problem converges rapidly and retains numerical stability for large models.
Abstract: A new methodology for performance analysis of flexible manufacturing systems (FMSs) with priority scheduling is presented. The analytic model developed extends the mean value analysis of closed networks of queues with multiple product types, various non-preemptive priority service disciplines, and with parallel machine stations. Performance measures derived include the expected throughput per product and per station, utilization of machines and transporters, queuing times and queue length measures for various configurations. Extensive numerical calculations have shown that the algorithm used for solving the problem converges rapidly and retains numerical stability for large models. The paper also illustrates the application of the model to a system with a mixture of FCFS and HOL disciplines which gives insights into various priority assignment policies in FMSs. Special attention was given to the problem of scheduling the robot carriers (transporters).

Journal Article
TL;DR: In this paper, efficient routing and scheduling strategies for heavy-demand corridors are described, and several strategies pertain to local service: shortturning, restricted zonal service, semirestricted zonal services, and limited-stop ZSL.
Abstract: Efficient routing and scheduling strategies for heavy-demand corridors are described. Examples are given. Four strategies pertain to local service: shortturning, restricted zonal service, semirestricted zonal service, and limitedstop zonal service. Zoning of express services and deadheading of both local and express service are also discussed. Advantages and disadvantages of the strategies, and conditions favoring their adoption, are discussed.

Book ChapterDOI
01 Jan 1985
TL;DR: In this paper, it is shown how to model with a timed Petri net, tasks, resources and constraints of a scheduling problem, and the results show how the model can be modified for discrete-time operations.
Abstract: In this paper, we show how to model with a timed Petri net, tasks, resources and constraints of a scheduling problem.

Journal ArticleDOI
TL;DR: A new two-phase approximate method for real-time scheduling in a flexible manufacturing system (FMS) that combines a reduced enumeration schedule generation algorithm with a 0–1 optimization algorithm and heuristic rules are introduced for the selection of jobs to be scheduled.
Abstract: This paper presents a new two-phase (TP) approximate method for real-time scheduling in a flexible manufacturing system (FMS). This method combines a reduced enumeration schedule generation algorithm with a 0–1 optimization algorithm. In order to make the combined algorithm practicable, heuristic rules are introduced for the selection of jobs to be scheduled. The relative performance of the TP method vis-a-vis conventional heuristic dispatching rules such as SPT, LPT, FCFS, MWKR, and LWKR is investigated using combined process-interaction/discrete-event simulation models. An efficient experimental procedure is designed and implemented using these models, and the statistical analysis of the results is presented. For the particular case investigated, the conclusions are very encouraging. In terms of mean flow time, the TP method performs significantly better than any other tested heuristic dispatching rules. Also, the experimental results show that using global information significantly improves the FMS performance.

Journal ArticleDOI
TL;DR: An integer programming model that portrays the architectural features of a class of vector and array processors has been developed and is used to produce optimal schedules for low-level-instruction codes of such processors.
Abstract: An integer programming model that portrays the architectural features of a class of vector and array processors has been developed. This model is used to produce optimal schedules for low-level-instruction codes of such processors. Optimal schedules are produced for both straight codes and instruction loops. Loop scheduling is separately considered because of special consideration that must be given to the effects of the instructions of consecutive loop iterations on each other that are hidden when static instruction scheduling approach is used. Using the model, a number of experiments have been conducted in optimal scheduling of Cray assembly codes.

Journal ArticleDOI
TL;DR: A heuristic algorithm CP/MISF (Critical Path/Most Immediate Successors First) and an optimization/approximation algorithm DF/IHS (Depth First/ Implicit Heuristic Search) are proposed which can reduce markedly the space complexity and average computation time.
Abstract: This paper describes practical optimization/approximation algorithms for scheduling a set of partially ordered computational tasks with different processing times onto a multiprocessor system so that the schedule length is minimized. Since this problem belongs to the class of “strong” NP hard problems, we must eliminate the possibility of constructing not only pseudopolynomial time optimization algorithms, but also fully polynomial time approximation schemes unless P = NP. This paper proposes a heuristic algorithm CP/MISF (Critical Path/Most Immediate Successors First) and an optimization/approximation algorithm DF/IHS (Depth First/ Implicit Heuristic Search). DF/IHS is an excellent scheduling method which can reduce markedly the space complexity and average computation time by combining the branch-and-bound method with CP/MISF; it allows us to solve very large-scale problems with a few hundred tasks.

Journal Article
TL;DR: In this paper, the authors studied the scheduling of multiple activities that require periodic processing on a single facility for an infinite horizon and proposed an ILP-based approach to solve the problem.
Abstract: This paper studies the scheduling of multiple activities that require periodic processing on a single facility for an infinite horizon. It first formulates this scheduling problem as an integer linear programming (ILP) model, and then uses the Chinese Remainder Theorem to efficiently partition the original into smaller independent models. For a small problem involving about 10 activities, the solution can be obtained very simply by hand. An example is given to illustrate the approach.

Journal ArticleDOI
TL;DR: A probabilistic analysis is presented for this NP-hard problem known as 1/rj/ΣCj in the scheduling literature and it is shown that the problem can be broken into 2 categories: the undersaturated and the oversaturated case.
Abstract: There are n jobs that have to be processed on one available machine. The ith job arrives at epoch r1 and it takes P1 units of time to carry out its operation. No preemptions are allowed. It is desired to minimize total flow time. A probabilistic analysis is presented for this NP-hard problem known as 1/rj/ΣCj in the scheduling literature. Under very general probability distributions of the problem data, it is shown that the problem can be broken into 2 categories: the undersaturated and the oversaturated case. Asymptotically optimal algorithms are presented for each case.

Journal ArticleDOI
TL;DR: The authors propose an efficient method of utilizing the primitive operations of collision detection and broadcast in multiaccess networks to efficiently distribute status information and to identify the extremum.
Abstract: A study of resource scheduling based on a distributed state-dependent discipline for a system of processors connected by a local multiaccess network is made. The scheduling problem is reduced to the identification of the extremum from a set of physically dispersed random numbers. The authors propose an efficient method of utilizing the primitive operations of collision detection and broadcast in multiaccess networks to efficiently distribute status information and to identify the extremum. The optimal performance of extremum identification is found to be constant and on the average independent of the number of contending processors. The protocol can be implemented either by minor hardware modification of existing multiaccess-network interfaces or in software.

Journal ArticleDOI
TL;DR: A flow model of an automated-printed circuit card assembly line at the International Business Machines Corporation (IBM) plant at Tucson, Arizona is described and it is demonstrated that the hierarchical strategy is effective in meeting production requirements while limiting average work-in-process (WIP).
Abstract: In this paper, we describe a flow model of an automated-printed circuit card assembly line at the International Business Machines Corporation (IBM) plant at Tucson, Arizona. We use a simulation based on this model as a test bed to discuss the performance of a hierarchical scheduling policy described in [3]. We compare this with other policies for loading parts into a flexible manufacturing system. We demonstrate that the hierarchical strategy is effective in meeting production requirements (both total volume and balance among part types) while limiting average work-in-process (WIP). This is a consequence of the feedback nature of the policy. Hedging (i.e. building up buffer stock) compensates for machine failures, thus resulting in high production percentages. The work-in-process (WIP) is low, as the policy reduces internal queues by respecting the capacity constraints of the system at every instant.

Proceedings ArticleDOI
15 Dec 1985
TL;DR: The use of a computer simulation model in evaluating the scheduling of surgical patients in an operating room using the concepts of block scheduling and example inputs, outputs, and uses are presented.
Abstract: This paper describes the use of a computer simulation model in evaluating the scheduling of surgical patients in an operating room. The concepts of block scheduling are discussed. An actual application of the model is described. Example inputs, outputs, and uses of the model are presented.


Proceedings ArticleDOI
01 Mar 1985
TL;DR: The Generalized Executive for real-time Multiprocessor applications (GEM) is an operating system that addresses several problems arising due to the unique requirements of operating software, including: (1) GEM supports two different sizes of tasks and task scheduling, called processes and micro-processes, and offers a variety of real- time scheduling calls, and (2) G EM supports multiple models of communication.
Abstract: To increase the speed and reliability of robots and of industrial control systems, multiple processing elements are used in their computing hardware. However, performance increases are not attained by hardware, alone. It is the hardware's operating software that must exploit the possible parallelism to gain the increases desired. Such software consists of control programs written by application programmers and operating system software offering means of task scheduling, inter-task communication, and hardware configuration control. The Generalized Executive for real-time Multiprocessor applications (GEM) is an operating system that addresses several problems arising due to the unique requirements of operating software, including: (1) GEM supports two different sizes of tasks and task scheduling, called processes and micro-processes, and offers a variety of real-time scheduling calls, and (2) GEM supports multiple models of communication.

Journal ArticleDOI
TL;DR: The use of multiple FIFO queues for nonpreemptive task scheduling is described and four multiple-queue scheduling algorithms with different placement policies are presented and applied to the PASM parallel processing system.
Abstract: PASM is a proposed large-scale distributed/parallel processing system which can be partitioned into independent SIMD/MIMD machines of various sizes. One design problem for systems such as PASM is task scheduling. The use of multiple FIFO queues for nonpreemptive task scheduling is described. Four multiple-queue scheduling algorithms with different placement policies are presented and applied to the PASM parallel processing system. Simulation of a queueing network model is used to compare the performance of the algorithms. Their performance is also considered in the case where there are faulty control units and processors. The multiple-queue scheduling algorithms can be adapted for inclusion in other multiple-SIMD and partitionable SIMD/MIMD systems that use similar types of interconnection networks to those being considered for PASM.

Journal ArticleDOI
Robbe J. Walstra1
01 Aug 1985
TL;DR: A new, iterative method for approximately analyzing closed networks of queues with nonexponential service time distributions and FCFS scheduling is proposed, based on the Principle of Maximum Entropy and produces results which are consistent with the fundamental Work Rate Theorem.
Abstract: We will propose a new, iterative method for approximately analyzing closed networks of queues with nonexponential service time distributions and FCFS scheduling. Our method is based on the Principle of Maximum Entropy and produces results which, first, are consistent with the fundamental Work Rate Theorem and, second, are exact for separable networks of queues. Considering accuracy and execution time characteristics, our method offers a viable alternative to Marie's homogeneous approximation method.

Journal ArticleDOI
TL;DR: A methodology to compare proposed finite element systems without implementing either hardware or software is presented and results provide a means of comparing proposed finiteelement systems.

Journal ArticleDOI
TL;DR: This article introduces a general iterative decomposition algorithm for permutation scheduling problems and applies it to the permutation flow shop scheduling problem, and develops bounds needed and two heuristic algorithms based on the iteratives decomposition approach.

Journal ArticleDOI
TL;DR: This paper extends the work of Chandy and Reynolds by showing that a policy maximizes the probability that all tasks finish by some time t≧0 if and only if the policy is Highest-Level-First (HLF).
Abstract: In this paper we extend the work of Chandy and Reynolds in which they considered the problem of scheduling tasks on two identical processors. The processing times of the tasks are independent, identically distributed exponential random variables. The tasks are subject to in-tree precedence constraints. Chandy and Reynolds have shown that the expected value of the makespan is minimized if and only if the scheduling policy is Highest-Level-First (HLF). We extend their result by showing that a policy maximizes the probability that all tasks finish by some time t≧0 if and only if the policy is HLF. Additionally, we show that a policy maximizes the probability that the sum of the finishing times of all the tasks is less than some value s≧0 if and only if the policy is HLF.

Journal ArticleDOI
TL;DR: The capacity estimation of data communication and telephone switching systems which, in addition to serving n queues cyclically, must execute maintenance (or other low-priority jobs) without severely disrupting the queues' performance is derived.
Abstract: In many data communication and telephone switching systems, one processor must perform more than one type of task. In some systems it is advantageous to place the different tasks in different queues and have the processor serve the queues in a cyclic manner. Moreover, the system design often imposes a (finite or infinite) limit on the number of entries that may be served per cycle from any given queue; this limit typically varies from queue to queue. This paper will derive the capacity estimation of such systems. We consider systems which, in addition to serving n queues cyclically, must execute maintenance (or other low-priority jobs) without severely disrupting the queues' performance. For two alternative methods of scheduling the maintenance, we compute steady state values of i) the average cycle time, ii) the average number of entries of each queue served per cycle, iii) the average time spent at each queue per cycle, iv) the average amount of elapsed time necessary to complete a given amount of maintenance execution real time, and v) if the arrival rate to queue i,\lambda_{i} , is proportional to N , the number of customers in the system, i.e., \lambda_{i} = N\alpha_{i} , then we a) compute the value of N which saturates the system and b) predict which queue will first become saturated as N is increased towards this value.