High Priority Jobs Research Articles

Symbiotic jobscheduling with priorities for a simultaneous multithreading processor

Simultaneous Multithreading machines benefit from jobscheduling software that monitors how well coscheduled jobs share CPU resources, and coschedules jobs that interact well to make more efficient use of those resources. As a result, informed coscheduling can yield significant performance gains over naive schedulers. However, prior work on coscheduling focused on equal-priority job mixes, which is an unrealistic assumption for modern operating systems.This paper demonstrates that a scheduler for an SMT machine can both satisfy process priorities and symbiotically schedule low and high priority threads to increase system throughput. Naive priority schedulers dedicate the machine to high priority jobs to meet priority goals, and as a result decrease opportunities for increased performance from multithreading and coscheduling. More informed schedulers, however, can dynamically monitor the progress and resource utilization of jobs on the machine, and dynamically adjust the degree of multithreading to improve performance while still meeting priority goals.Using detailed simulation of an SMT architecture, we introduce and evaluate a series of five software and hardware-assisted priority schedulers. Overall, our results indicate that coscheduling priority jobs can significantly increase system throughput by as much as 40%, and that (1) the benefit depends upon the relative priority of the coscheduled jobs, and (2) more sophisticated schedulers are more effective when the differences in priorities are greatest. We show that our priority schedulers can decrease average turnaround times for a random jobmix by as much as 33%.

410 ホロニック生産システムにおけるリアルタイムスケジューリング : スケジューリングにおけるシミュレーションの適用

This paper deals with real-time scheduling system in a holonic manufacturing system for machining process. The holonic manufacturing system was proposed by HMS cooperative research project aiming at realizing more flexible control structures of the manufacturing system which can cope with the variety of the products and the unscheduled disruptions, such as status changes of equipment and input of high priority jobs. Decision making processes of Holons are newly proposed here to satisfy not only flexibility but also optimality of real-time scheduling in HMS.

101 ホロニック生産システムのスケジューリングに関する研究

This paper deals with a real time scheduling system of a holonic manufacturing system for machining process. The holonic manufacturing system was proposed by HMS cooperative research project aiming at realizing more flexible control structures of the manufacturing systems which can cope with the variety of the products and the unscheduled disruption, such as status changes of equipment and input of high priority jobs. Decision-making procedures of individual holons are discussed in the paper to establish a decision making process based on effectiveness for the holonic real time scheduling systems.

Solution of One Problem of Resource Allocation in Real-Time Automated Control System in the Presence of Uncertain Factors

The problem of allocating the amended resources in a real-time automated control system under a constrained time of executing the given assembly of uninterrupted jobs was considered. At some indefinite time instants, the resources available can be given to higher-priority jobs. As the result, execution of the initial job assembly is suspended, thus violating the initial schedule. A strategy of constructing admissible schedules with the minimum probability of their violation was developed.

F-0613 ホロニック生産システムのシミュレーションのためのインタフェースシステムの開発(S42-2 生産システムにおけるソフトウェア技術(2))(S42 生産システムにおけるソフトウェア技術)

This paper deals with a simulation system for holonic manufacturing systems. The holonic manufacturing system was proposed by HMS cooperative research project aiming at realizing more flexible control structures of the manufacturing system which can cope with the variety of the products and the unscheduled disruptions, such as break down of equipment and input of high priority jobs. A real-time scheduling procedure is implemented in the holonic manufacturing system simulation. A user interface system is developed in the study to provide the manufacturing engineers with interactive methods to change the status of the equipment and the jobs. The simulation system is applied to the holonic manufacturing system simulation for adding the high priority jobs and for changing the equipment status.

Labour flexibility and assignment policies in a job shop having incommensurable objectives

This study evaluates operating policies for offering a near-perfect delivery performance for vital customers in dual resource-constrained (DRC) job shop environments. Prior studies have considered this problem in machine-limited settings, and shown that dispatching rules that help realise a near-perfect delivery performance for vital customers necessarily deteriorate delivery performance for other customers served by the shop. This study extends prior work, and considers additional tools that can be used by managers in DRC shops such as labour flexibility, and assignment rules that incorporate customer-based information to deploy workers to departments containing high-priority jobs. Results show that labour flexibility in conjunction with appropriate decision rules allows for enhanced delivery performance for both vital and normal priority customers. These results hold even under conditions where 80% of the shop's workload is compromised of high-priority orders.

Ergonomic Hand tool Interventions for the Furniture Manufacturing Industry

This project focused on the development of ergonomic interventions to reduce the incidence of musculoskeletal problems in the furniture manufacturing industry. The results of an industry-based survey provided a list of the high priority jobs to be addressed with ergonomic interventions. This paper focuses on the development and evaluation of two of these interventions: an upholstery hand tool and an ergonomic interface for a random orbital sander. Laboratory testing was performed to examine the ergonomic issues with use of each intervention. A reduction in risk factors was found with use of the interventions. The upholstery hand tool reduced grip force from 36 to 18 N, improved hand posture by changing from a pinch grip to a power grip, and reduced the repetition rate from 40 to 24 repetitions per minute. EMG analysis of intrinsic and extrinsic muscles showed a reduction in overall muscle activity and a shift from the intrinsic muscles to the extrinsic finger flexor muscles. The ergonomic interface for the random orbital sander was designed to reduce exposure to vibration and eliminate the need for sustained, static grip force. A subjective survey of users revealed both a short and long term improvement in user comfort and fatigue, while a pre-post study design revealed no significant change in grip strength.

Editorial

This paper investigates replanning strategies for container-transportation task allocation of autonomous Straddle Carriers (SC) at automated container terminals. The strategies address the problem of large-scale scheduling in the context of uncertainty (especially uncertainty associated with unexpected events such as the arrival of a new task). Two rescheduling policies–Rescheduling New arrival Jobs (RNJ) policy and Rescheduling Combination of new and unexecuted Jobs (RCJ) policy–are presented and compared for long-term Autonomous SC Scheduling (ASCS) under the uncertainty of new job arrival. The long-term performance of the two rescheduling policies is evaluated using a multi-objective cost function (i.e., the sum of the costs of SC travelling, SC waiting, and delay of finishing high-priority jobs). This evaluation is conducted based on two different ASCS solving algorithms–an exact algorithm (i.e., branch-and-bound with column generation (BBCG) algorithm) and an approximate algorithm (i.e., auction algorithm)–to get the schedule of each short-term planning for the policy. Based on the map of an actual fully-automated container terminal, simulation and comparative results demonstrate the quality advantage of the RCJ policy compared with the RNJ policy for task allocation of autonomous straddle carriers under uncertainty. Long-term testing results also show that although the auction algorithm is much more efficient than the BBCG algorithm for practical applications, it is not effective enough, even when employed by the superior RCJ policy, to achieve high-quality scheduling of autonomous SCs at the container terminals.

Asymptotic loss of priority scheduling policies in closed re-entrant lines: A computational study

In this paper we present an approximate but efficient analytical method to compute the asymptotic loss of buffer priority scheduling policies in closed re-entrant lines. For simple two-station closed re-entrant lines, this enables the verification of Harrison-Wein conjectures and Jin-Ou-Kumar resuts. For multi-station re-entrant lines, this provides an efficient way of comparing different buffer priority scheduling policies. We also use the method to evaluate the effect of high priority jobs in re-entrant lines.

Matrix-geometric solution of discrete time MAP/PH/1 priority queue

We use the matrix-geometric method to study the discrete time MAP/PH/1 priority queue with two types of jobs. Both preemptive and non-preemptive cases are considered. We show that the structure of the R matrix obtained by Miller for the Birth-Death system can be extended to our Quasi-Birth-Death case. For both preemptive and non-preemptive cases the distributions of the number of jobs of each type in the system are obtained and their waiting times are obtained for the non-preemptive. For the preemptive case we obtain the waiting time distribution for the high priority job and the distribution of the lower priority job's wait before it becomes the leading job of its priority class. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 23–50, 1998

Transient analysis of multiclass manufacturing systems with priority scheduling

In this article we examine the transient performance of a flexible machine centre that processes several classes of jobs with significant setup times and with priority scheduling. Our results show that the transient performance of the system over typical observation intervals can be significantly different from the performance predicted by steady-state analysis. The machine centre serves three classes of jobs—class 1, class 2 and class 3; class 3 jobs have non-preemptive priority over jobs of class 1 and class 2. The results show that the throughput and cycle time of class 1 and class 2 jobs are affected quite dramatically by the arrival of class 3 jobs. However, over a typical observation period in the initial evolution of the system, steady-state results overestimate this effect of the high priority jobs whereas the more credible estimates are given by transient analysis. The transient analysis is carried out by solving explicitly the corresponding Markov chains, using a higher level stochastic Petri net model to generate the Markov chains.

Modeling the effect of hot lots in semiconductor manufacturing systems

The presence of hot lots or high-priority jobs in semiconductor manufacturing systems is known to significantly affect the cycle time and throughput of the regular lots since the hot lots get priority at all stages of processing. In this paper, we present an efficient analytical model based on re-entrant lines and use an efficient, approximate analysis methodology for this model in order to predict the performance of a semiconductor manufacturing line in the presence of hot lots. The proposed method explicitly models scheduling policies and can be used for rapid performance analysis. Using the analytical method and also simulation, we analyze two re-entrant lines, including a full-scale model of a wafer fab, under various buffer priority scheduling policies. The numerical results show the severe effects hot lots can have on the performance characteristics of regular lots.

COMPOUND DYNAMIC EVENT METAMODELS FOR ELECTRONIC ASSEMBLY LINE SYSTEMS

In the assembly line systems of the electronics industry, production controls based on steady-state conditions have proved ineffectual in coping with dynamic events, such as machine breakdowns, part supply shortages, and high priority job order processing, which can occur individually or simultaneously. There are few tools that give results quickly as to how many assemblies will be delayed by a dynamic event and how long it will take to recover from the impact. Computer simulation is available, but its lengthy execution time has hindered its application in real time. Previous research discovered that the patterns of these dynamic events can be represented by metamodels in the solution form of first order systems. In this paper, these results are unified and it is further shown that compound dynamic event metamodels can be developed from the individual metamodels using linear additivity. These metamodels are fit to the output from the simulation; and the resulting equations can be used in real time to meas...

Analysis of the M/G/1 queue under a combined preemptive/nonpreemptive priority discipline

The authors propose a combined preemptive/nonpreemptive priority discipline. When a high-priority job arrives at the system while a low-priority job is being in service, the high-priority job will be served immediately and the low-priority job will go back to the head of the queue of its class, if a discretion rule for preemption is satisfied. Otherwise, the high-priority job waits in queue until the completion of the low-priority job service. As the discretion rule for preemption, three schemes are considered, each based on the parameter of the low-priority job: the elapsed service time, the ratio of elapsed to total service time, and the remaining service time. Using the busy-period analysis technique, an M/G/1 queueing system with multiple priority classes of jobs is analyzed. Considered preemptive rules are the preemptive-resume and preemptive-repeat-identical policies. As results, the Laplace transforms associated with waiting time and response time, and the z-transform for the number of jobs in the system as well as their expectations are presented. >

Assembly line system dynamic behaviour for high priority job order processing

Very often in a manufacturing plant, an important job order must be processed with higher priority than other regular jobs. It is vital for management to understand the impact on production performance of these high priority job orders. In this paper, this dynamic behaviour of assembly line systems is studied using computer simulation and derived metamodels in the form of mathematical expressions. An extensive computer simulation study is first conducted off-line. Next, analytical representations of the system lmetamodels) are fitted to the dynamic behaviour as simulated. These relatively simple equations can then be used on-line to estimate the impact of high priority job order processing when it occurs. The results indicate that the system response to this dynamic event can be described by first-order exponential delay functions captured in metamodels from simulation results. Using only the metamodels, the finish time of high priority jobs can be predicted and the number of delayed regular assembly products can be estimated in real time in the shop floor. This information is very valuable and useful for production scheduling.

A metamodel-based decision support system for shop floor production control

Due to the lack of viable modeling techniques, abnormal situations at the operational level in a dynamic manufacturing environment cannot be handled by shop floor production control systems that are only applicable to steady-state performance. A tool is needed for the management in dealing with unexpected real-time events. In this paper, we present a decision support system (DSS) that estimates late-finishing parts in an assembly system due to machine breakdown, part supply shortage and processing of high-priority jobs. The application program, desc (Dynamic Evaluator of Simulated Consequences), is based on dynamic metamodels developed from computer simulation results. The DSS development procedure is discussed and its use is demonstrated by an example using data from a printed circuit board (PCB) assembly plant. Since no time-consuming simulation is necessary at the shop floor, the metamodel-based DSS can provide valuable information for making real-time production control decisions.

Estimating simulation metamodel parameters for unexpected shop floor real time events

Abstract In order to better understand assembly line system dynamic behavior and provide a basis for developing effective production controls, three unexpected real time events are studied, including sudden machine breakdown at a work station, parts supply shortage and high priority job order processing. Short term system performance is evaluated by dynamic response variables associated with assembly time and work in process (WIP) inventory. Simulation is used as the modeling tool, and the results are further described by mathematical metamodels for overall system behavior. The system transients can be adequately represented by first order exponential functions, and satisfactory results are also obtained for expressing simultaneous occurrence of dynamic events by combined metamodels using linear additivity. A procedure is proposed for the development of dynamic metamodels. For a given system, only a limited number of simulation runs should be made in advance to estimate the metamodel parameters. Using the resultant application program that only contains the metamodels, whenever an event occurs, without running simulation a user can instantaneously predict the consequence in a specified time period by an estimation to the number of assembly products to be finished late.

A Knowledge-Based Production Control System to Accommodate Unscheduled Disruptions in the Manufacturing Process

This paper deals with a knowledge-based production control system to accommodate unscheduled disruptions, such as the breakdown of machines, high-priority jobs, and power failures. In particular, we mainly discuss the representation and utilization of experiential knowledge concerning the counterplans against unscheduled disruptions in the manufacturing process. A hierarchical method was proposed to represent a set of rules concerning the counterplans. A knowledge based system was implemented based on the representation method. It has been shown through case studies that the system is effective in selecting suitable counterplans against unscheduled disruptions.

Simulation of a clinical chemistry laboratory

Using a general purpose simulation system (GPSS), we have attempted to objectively evaluate general operation of a routine clinical chemistry service laboratory and identify the bottlenecks (BN). In view of these BN, a solution is proposed to upgrade the quality of the service rendered. We have used the essential elements, such as job, people, and equipment in their independant cycles. During the states of processing, all the phases and the elements were synchronized to perform as an integrated system functions. The overall main model consists of conventional GPSS bloeks used in a sequential manner of their appearance. Blocks like GENERATE, QUEUE, DEPART, SEIZE, and RELEASE were used with an ADVANCE block to denote a prescribed length of time spent in a given stage. The ASSIGN, TEST and PRIORITY (BUFFER) blocks were used to determine some priority levels (routine, stat and super-stat) for all the chemistry test requests. Certain valid assumptions regarding the availability and down-time of equipment were specified. Equipment and manpower models were used for simulating UNAVAILABLE conditions in each case. After the samples were tested, passed through a quality control check and approved for reporting, the biggest BN in the simulation was encountered at the charting and reporting stations. The high priority job (initiated at random) was serviced without delay and the processing was completed without added strain on the resources. A trained technologist (a specified resource) was not utilized for all of the job expected of him. It appears that even with the full resources made available, essentially the job description and performance of the job according to the specifications play an important role for the cost effective and improved efficiency of a clinical laboratory performing routine chemistry services.

Scheduling according to job priority with prevention of deadlock and permanent blocking

Some job scheduling algorithms have been developed which prevent deadlock and permanent blocking. The jobs are assumed to be ordered according to a priority rule indicating the order in which requests for resources should be considered. Each job has an upper limit on the resources demanded, and each job will eventually return all resources allocated to it. The main advantages of the developed algortihms are: A. New low priority jobs will never block older higher priority jobs. B. Requests are always granted if they cannot delay higher priority jobs. C. Any priority rule may be chosen.