Showing papers on "Scheduling (computing) published in 1997"

Method and apparatus for scheduling the presentation of messages to computer users

Abstract: The present invention provides a method and apparatus for scheduling the presentation of a continuously-changing display (702) to computer users, and is particularly well-suited for use in an advertisement-supported e-mail service. An advertisement display scheduler (700) resident on a user's computer receives advertisements from a server system over a network. Upon receipt, the advertisement display scheduler (700) determines the priority of the advertisement (MSG01 .... MSGnn) and assigns it to one of a plurality of prioritized advertisement queues (Qo .... Qn). Each queue is sorted (701) according to predetermined scheduling criteria so that advertisements deemed 'more important' are presented to a user first. The advertisement display scheduler (700) logs statistical information relating to the presentation of advertisements for use in updating the scheduling criteria, and makes such statistical information available to the server system.

A resource estimation and call admission algorithm for wireless multimedia networks using the shadow cluster concept

Abstract: The shadow cluster concept can be used to estimate future resource requirements and to perform call admission decisions in wireless networks. Shadow clusters can be used to decide if a new call can be admitted to a wireless network based on its quality-of-service (QoS) requirements and local traffic conditions. The shadow cluster concept can especially be useful in future wireless networks with microcellular architectures where service will be provided to users with diverse QoS requirements. The framework of a shadow cluster system is completely distributed, and can be viewed as a message system where mobile terminals inform the base stations in their neighborhood about their requirements, position, and movement parameters. With this information, base stations predict future demands, reserve resources accordingly, and admit only those mobile terminals which can be supported adequately. The shadow cluster concept involves some processing and communication overheads. These overheads have no effect on wireless resources, but only on the base stations and the underlying wireline network. It is shown how base stations determine the probabilities that a mobile terminal will be active in other cells at future times, define and maintain shadow clusters by using probabilistic information on the future position of their mobile terminals with active calls, and predict resource demands based on shadow cluster information. In addition, a call admission algorithm is introduced, which uses current traffic and bandwidth utilization conditions, as well as the amount of resources and maximum allowable "dropping probability" being requested. Performance results showing the advantages of the shadow cluster concept are also included.

Start-time fair queueing: a scheduling algorithm for integrated services packet switching networks

Abstract: We present a start-time fair queueing (SFQ) algorithm that is computationally efficient and achieves fairness regardless of variation in a server capacity. We analyze its single server and end-to-end deadline guarantee for variable rate fluctuation constrained (FC) and exponentially bounded fluctuation (EBF) servers. To support heterogeneous services and multiple protocol families in integrated services networks, we present a hierarchical SFQ scheduler and derive its performance bounds. Our analysis demonstrates that SFQ is suitable for integrated services networks since it: (1) achieves low average as well as maximum delay for low-throughput applications (e.g., interactive audio, telnet, etc.); (2) provides fairness which is desirable for VBR video; (3) provides fairness, regardless of variation in server capacity, for throughput-intensive, flow-controlled data applications; (4) enables hierarchical link sharing which is desirable for managing heterogeneity; and (5) is computationally efficient.

Theory and Practice in Parallel Job Scheduling

Abstract: The scheduling of jobs on parallel supercomputer is becoming the subject of much research. However, there is concern about the divergence of theory and practice. We review theoretical research in this area, and recommendations based on recent results. This is contrasted with a proposal for standard interfaces among the components of a scheduling system, that has grown from requirements in the field.

Scheduling real-time applications in an open environment

Abstract: This paper extends the two-level hierarchical scheme in (Deng et al., 1997) for scheduling independently developed real-time applications with non-real-time applications in an open environment. The environment allows the schedulability of each real-time application to be validated independently of other applications in the system. The extended scheme removes the following two restrictions of the scheme: real-time applications that are scheduled preemptively must consist solely of periodic tasks; and applications must not share global resources (i.e., resources used by more than one application). Consequently, the extended scheme can accommodate a much broader spectrum of real-time applications.

Hierarchical packet fair queueing algorithms

Abstract: We propose to use the idealized hierarchical generalized processor sharing (H-GPS) model to simultaneously support guaranteed real-time, rate-adaptive best-effort, and controlled link-sharing services. We design hierarchical packet fair queueing (H-PFQ) algorithms to approximate H-GPS by using one-level variable-rate PFQ servers as basic building blocks. By computing the system virtual time and per packet virtual start/finish times in unit of bits instead of seconds, most of the PFQ algorithms in the literature can be properly defined as variable-rate servers. We develop techniques to analyze delay and fairness properties of variable-rate and hierarchical PFQ servers. We demonstrate that in order to provide tight delay bounds with an H-PFQ server, it is essential for the one-level PFQ servers to have small worst-case fair indices (WFI). We propose a new PFQ algorithm called WF/sup 2/Q+ that is the first to have all the following three properties: (1) providing the tightest delay bound among all PFQ algorithms; (2) having the smallest WFI among all PFQ algorithms; and (3) having a relatively low asymptotic complexity of O(log N). Simulation results are presented to evaluate the delay and link-sharing properties of H-WF/sup 2/Q+, H-WFQ, H-SFQ, and H-SCFQ.

Method and apparatus for reverse link rate scheduling

Abstract: In a communication system capable of variable rate transmission, multi-level scheduling improves utilization of the reverse link and decreases the transmission delay in data communication. Multi-level scheduling comprises base station level scheduling, selector level (system level) scheduling, and network level scheduling. Network level scheduling is performed for base station in soft handoff with base stations which are controlled by different selector scheduler. Selector level scheduling is performed for remote stations in soft handoff with base stations which are controlled by the same selector scheduler. And base station level scheduling is performed for remote stations not in soft handoff. Base station level scheduled is performed using residual capacity after higher level scheduling have been performed. Each scheduling level can have different scheduling interval.

Eliminating receive livelock in an interrupt-driven kernel

Abstract: Most operating systems use interface interrupts to schedule network tasks. Interrupt-driven systems can provide low overhead and good latency at low offered load, but degrade significantly at higher arrival rates unless care is taken to prevent several pathologies. These are various forms ofreceive livelock, in which the system spends all of its time processing interrupts, to the exclusion of other necessary tasks. Under extreme conditions, no packets are delivered to the user application or the output of the system. To avoid livelock and related problems, an operating system must schedule network interrupt handling as carefully as it schedules process execution. We modified an interrupt-driven networking implementation to do so; this modification eliminates receive livelock without degrading other aspects of system performance. Our modifications include the use of polling when the system is heavily loaded, while retaining the use of interrupts ur.Jer lighter load. We present measurements demonstrating the success of our approach.

A web calendar architecture and uses thereof

Abstract: An architecture for facilitating Web based Calendar client side event scheduling and, the association process between Java calendar applet ('Capplet') and calendar event. Internet scheduling and calendaring groupware that coordinates group schedules. It features concurrent Capplets running within any of the four calendar grids, namely, monthly, weekly, multiple days and daily.

CPU reservations and time constraints: efficient, predictable scheduling of independent activities

Abstract: Workstations and personal computers are increasingly being used for applications with real-time characteristics such as speech understanding and synthesis, media computations and I/O, and animation, often concurrently executed with traditional non-real-time workloads. This paper presents a system that can schedule multiple independent activities so that: . activities can obtain minimum guaranteed execution rates with application-specified reservation granularities via CPU Reservations, CPU Reservations, which are of the form reserve X units of time out of every Y units, provide not just an average case execution rate of X/Y over long periods of time, but the stronger guarantee that from any instant of time, by Y time units later, the activity will have executed for at least X time units, . applications can use Time Constraints to schedule tasks by deadlines, with on-time completion guaranteed for tasks with accepted constraints, and . both CPU Reservations and Time Constraints are implemented very efficiently. In particular, . CPU scheduling overhead is bounded by a constant and is not a function of the number of schedulable tasks. Other key scheduler properties are: . activities cannot violate other activities' guarantees, . time constraints and CPU reservations may be used together, separately, or not at all (which gives a round-robin schedule), with well-defined interactions between all combinations, and . spare CPU time is fairly shared among all activities. The Rialto operating system, developed at Microsoft Research, achieves these goals by using a precomputed schedule, which is the fundamental basis of this work.

Method and system for monitoring call center service representatives

Abstract: A method and system permit monitoring of a call center agent or similar service representative in servicing calls in a call center using a variety of scheduling criteria. Monitoring schedules for the service representatives may be based on monitoring periods having scheduling criteria, such as a time interval, a scheduling rule, a number of calls, a monitoring length, a random indicator, call type information, agent performance level information, call traffic information, and others. The method and system record a customer call if the scheduling criteria of the associated monitoring period is met.

The performance of μ-kernel-based systems

Abstract: First-generation μ-kernels have a reputation for being too slow and lacking sufficient flexibility. To determine whether L4, a lean second-generation μ-kernel, has overcome these limitations, we have repeated several earlier experiments and conducted some novel ones. Moreover, we ported the Linux operating system to run on top of the L4 μ-kernel and compared the resulting system with both Linux running native, and MkLinux, a Linux version that executes on top of a first-generation Mach-derived μ-kernel. For L 4 Linux, the AIM benchmarks report a maximum throughput which is only 5% lower than that of native Linux. The corresponding penalty is 5 times higher for a co-located in-kernel version of MkLinux, and 7 times higher for a user-level version of MkLinux. These numbers demonstrate both that it is possible to implement a high-performance conventional operating system personality above a μ-kernel, and that the performance of the μ-kernel is crucial to achieve this. Further experiments illustrate that the resulting system is highly extensible and that the extensions perform well. Even real-time memory management including second-level cache allocation can be implemented at user-level, coexisting with L 4 Linux.

Fast Incremental Maintenance of Approximate Histograms

Abstract: Many commercial database systems maintain histograms to summarize the contents of large relations and permit efficient estimation of query result sizes for use in query optimizers. Delaying the propagation of database updates to the histogram often introduces errors into the estimation. This article presents new sampling-based approaches for incremental maintenance of approximate histograms. By scheduling updates to the histogram based on the updates to the database, our techniques are the first to maintain histograms effectively up to date at all times and avoid computing overheads when unnecessary. Our techniques provide highly accurate approximate histograms belonging to the equidepth and Compressed classes. Experimental results show that our new approaches provide orders of magnitude more accurate estimation than previous approaches.An important aspect employed by these new approaches is a backing sample, an up-to-date random sample of the tuples currently in a relation. We provide efficient solutions for maintaining a uniformly random sample of a relation in the presence of updates to the relation. The backing sample techniques can be used for any other application that relies on random samples of data.

Scheduling Theory and its Applications

Abstract: (1997). Scheduling Theory and its Applications. Journal of the Operational Research Society: Vol. 48, No. 7, pp. 764-765.

Forecasting network performance to support dynamic scheduling using the network weather service

Abstract: The Network Weather Service is a generalizable and extensible facility designed to provide dynamic resource performance forecasts in metacomputing environments. In this paper, we outline its design and detail the predictive performance of the forecasts it generates. While the forecasting methods are general, we focus on their ability to predict the TCP/IP end-to-end throughput and latency that is attainable by an application using systems located at different sites. Such network forecasts are needed both to support scheduling, and by the metacomputing software infrastructure to develop quality-of-service guarantees.

The design, implementation and evaluation of SMART: a scheduler for multimedia applications

Abstract: Real-time applications such as multimedia audio and video are increasingly populating the workstation desktop. To support the execution of these applications in conjunction with traditional non-realtime applications, we have created SMART, a Scheduler for Multimedia And Real-Time applications. SMART supports applications with time constraints, and provides dynamic feedback to applications to allow them to adapt to the current load. In addition, the support for real-time applications is inte grated with the support for conventional computations. This allows the user to prioritize across real-time and conventional computations, and dictate how the processor is to be shared among applications of the same priority . As the system load changes, SMART adjusts the allocation of resources dynamically and seamlessly. SMAR T is unique in its ability to automatically shed real-time tasks and re gulate their execution rates when the system is overloaded, while providing better value in underloaded conditions than previously proposed schemes. We have implemented SMART in the Solaris UNIX operating system and measured its performance against other schedulers in e xecuting real-time, interacti ve, and batch applications. Our results demonstrate SMART’s superior performance in supporting multimedia applications.

New Benchmark Results for the Resource-Constrained Project Scheduling Problem

Abstract: This paper reports on new insights derived from computational results obtained with an updated version of the branch-and-bound procedure previously developed by Demeulemeester and Herroelen Demeulemeester, E., W. Herroelen. 1992. A branch-and-bound procedure for the multiple resource-constrained project scheduling problem. Management Sci.38 1803-1818. for solving the resource-constrained project scheduling problem RCPSP. The new code fully exploits the advantages of 32-bit programming provided by recent compilers running on platforms such as Windows NT® and OS/2®: flat memory, increased addressable memory, and fast program execution. We study the impact of three important variables on the computation time for the RCPSP: addressable computer memory, the search strategy depth-first, best-first, or hybrid, and the introduction of a stronger lower bound. We compare the results obtained by a truncated branch-and-bound procedure with the results generated by the minimum slack time heuristic and report on the dependency of its solution quality on the allotted CPU time.

Graphical computer system and method for appointment scheduling

Abstract: A computer program stored in a storage medium and a computer-implemented method for scheduling appointments for an office or business includes program code for displaying screen displays on a computer monitor, including a day view screen display (18) with a plurality of thermometer-style schedules (43) having a vertical bar graph (44) opposite a daily appointment file (45) having multiple rows for entering appointment data. A horizontal scroll bar (48) allows the schedules to be displayed over a distance that is wider than a display area on the screen. The vertical bar graph (44) includes color-coded bars (47) to signify the status of appointments as: i) prior to check-in, ii) after check-in and iii) canceled appointments. In a "day view" schedules are arranged by selecting a group from a group list (24). The appointments can be predetermined as to type and duration, and a scheduler can refer to a list (63) of such pre-configured appointments (65) in scheduling patients. Various types of color-coding arrangements and icons are provided for patient status.

Improved Utilization and Responsiveness with Gang Scheduling

Abstract: Most commercial multicomputers use space-slicing schemes in which each scheduling decision has an unknown impact on the future: should a job be scheduled, risking that it will block other larger jobs later, or should the processors be left idle for now in anticipation of future arrivals? This dilemma is solved by using gang scheduling, because then the impact of each decision is limited to its time slice, and future arrivals can be accommodated in other time slices. This added flexibility is shown to improve overall system utilization and responsiveness. Empirical evidence from using gang scheduling on a Cray T3D installed at Lawrence Livermore National Lab corroborates these results, and shows conclusively that gang scheduling can be very effective with current technology.

A Historical Application Profiler for Use by Parallel Schedulers

Abstract: Scheduling algorithms that use application and system knowledge have been shown to be more effective at scheduling parallel jobs on a multiprocessor than algorithms that do not. This paper focuses on obtaining such information for use by a scheduler in a network of workstations environment.

Current trends in deterministic scheduling

Abstract: Scheduling is concerned with allocating limited resources to tasks to optimize certain objective functions. Due to the popularity of the Total Quality Management concept, on-time delivery of jobs has become one of the crucial factors for customer satisfaction. Scheduling plays an important role in achieving this goal. Recent developments in scheduling theory have focused on extending the models to include more practical constraints. Furthermore, due to the complexity studies conducted during the last two decades, it is now widely understood that most practical problems are NP-hard. This is one of the reasons why local search methods have been studied so extensively during the last decade. In this paper, we review briefly some of the recent extensions of scheduling theory, the recent developments in local search techniques and the new developments of scheduling in practice. Particularly, we survey two recent extensions of theory: scheduling with a 1-job-on-r-machine pattern and machine scheduling with availability constraints. We also review several local search techniques, including simulated annealing, tabu search, genetic algorithms and constraint guided heuristic search. Finally, we study the robotic cell scheduling problem, the auto-mated guided vehicles scheduling problem, and the hoist scheduling problem.

Deadline assignment in a distributed soft real-time system

Abstract: In a distributed environment, tasks often have processing demands at multiple different sites. A distributed task is usually divided into several subtasks, each to be executed in order at some site. In a real-time system, an overall deadline is usually specified by an application designer indicating when a distributed task is to be finished. In this paper, we present and analyze techniques for automatically translating the overall deadline into deadlines for the individual subtasks.

Fair scheduling in wireless packet networks

Abstract: Fair scheduling of delay and rate-sensitive packet flows over a wireless channel is not addressed effectively by most contemporary wireline fair scheduling algorithms because of two unique characteristics of wireless media: (a) bursty channel errors, and (b) location-dependent channel capacity and errors. Besides, in packet cellular networks, the base station typically performs the task of packet scheduling for both downlink and uplink flows in a cell; however a base station has only a limited knowledge of the arrival processes of uplink flows.In this paper, we propose a new model for wireless fair scheduling based on an adaptation of fluid fair queueing to handle location-dependent error bursts. We describe an ideal wireless fair scheduling algorithm which provides a packetized implementation of the fluid model while assuming full knowledge of the current channel conditions. For this algorithm, we derive the worst-case throughput and delay bounds. Finally, we describe a practical wireless scheduling algorithm which approximates the ideal algorithm. Through simulations, we show that the algorithm achieves the desirable properties identified in the wireless fluid fair queueing model.

Broadcast scheduling for information distribution

Abstract: Broadcast data delivery is encountered in many applications where there is a need to disseminate information to a large user community in a wireless asymmetric communication environment. We consider the problem of scheduling the data broadcast such that the access latency experienced by the users is low. In a push-based system, where the users cannot place requests directly to the server and the broadcast schedule should be determined based solely on the access probabilities, we formulate a deterministic dynamic optimization problem, the solution of which provides the optimal broadcast schedule. Properties of the optimal solution are obtained and then we propose a suboptimal dynamic policy which achieves mean access latency close to the lower bound. The policy has low complexity, it is adaptive to changing access statistics, and is easily generalized to multiple broadcast channels. In a pull-based system where the users may place requests about information items directly to the server, the scheduling can be based on the number of pending requests for each item. Suboptimal policies with good performance are obtained in this case as well. Finally, it is demonstrated by a numerical study that as the request generation rate increases, the achievable performance of the pull- and push-based systems becomes almost identical.

A hierarchical fair service curve algorithm for link-sharing, real-time and priority services

Abstract: In this paper, we study hierarchical resource management models and algorithms that support both link-sharing and guaranteed real-time services with decoupled delay (priority) and bandwidth allocation. We extend the service curve based QoS model, which defines both delay and bandwidth requirements of a class, to include fairness, which is important for the integration of real-time and hierarchical link-sharing services. The resulting Fair Service Curve link-sharing model formalizes the goals of link-sharing and real-time services and exposes the fundamental tradeoffs between these goals. In particular, with decoupled delay and band-width allocation, it is impossible to simultaneously provide guaranteed real-time service and achieve perfect link-sharing. We propose a novel scheduling algorithm called Hierarchical Fair Service Curve (H-FSC) that approximates the model closely and efficiently. The algorithm always guarantees the performance for leaf classes, thus ensures real-time services, while minimizing the discrepancy between the actual services provided to the interior classes and the services defined by the Fair Service Curve link-sharing model. We have implemented the H-FSC scheduler in the NetBSD environment. By performing simulation and measurement experiments, we evaluate the link-sharing and real-time performances of H-FSC, and determine the computation over-head.

Daily Aircraft Routing and Scheduling

Abstract: In this paper we consider the daily aircraft routing and scheduling problem DARSP. It consists of determining daily schedules which maximize the anticipated profits derived from the aircraft of a heterogeneous fleet. This fleet must cover a set of operational flight legs with known departure time windows, durations and profits according to the aircraft type. We present two models for this problem: a Set Partitioning type formulation and a time constrained multicommodity network flow formulation. We describe the network structure of the subproblem when a column generation technique is applied to solve the linear relaxation of the first model and when a Dantzig-Wolfe decomposition approach is used to solve the linear relaxation of the second model. The linear relaxation of the first model provides upper bounds. Integer solutions to the overall problem are derived through branch-and-bound. By exploiting the equivalence between the two formulations, we propose various optimal branching strategies compatible with the column generation technique. Finally we report computational results obtained on data provided by two different airlines. These results show that significant profit improvement can be generated by solving the DARSP using our approach and that this can be obtained in a reasonable amount of CPU time.

Effects of Objective and Subjective Task Complexity on Performance

Abstract: The thesis of this research is that performance on a task depends not only on objective complexity (a task characteristic) but also on one's perception of task complexity. This study allowed investigation of the influences of (a) cognitive ability, (b) motivation, (c) subjective task complexity, and (d) task experience on performance for an objectively simple or complex scheduling task. Potential determinants of subjective complexity were also studied, as well as the mediating effects of subjective complexity on the relations between independent variables (i.e., objective complex- ity, cognitive ability, and task experience) and task performance. Participants (N = 195) were undergraduates who prepared a 1-week work schedule for a fictitious film processing store under either a Simple or Complex condition. Those in the Complex condition were additionally required to account for employee time off and varying store traffic. Hierarchical regression revealed significant, unique main effects for objective task ...

Approximation techniques for average completion time scheduling

Abstract: We consider the problem of nonpreemptive scheduling to minimize average (weighted) completion time, allowing for release dates, parallel machines, and precedence constraints. Recent work has led to constant-factor approximations for this problem, based on solving a preemptive or linear programming relaxation and then using the solution to get an ordering on the jobs. We introduce several new techniques which generalize this basic paradigm. We use these ideas to obtain improved approximation algorithms for one-machine scheduling to minimize average completion time with release dates. In the process, we obtain an optimal randomized on-line algorithm for the same problem that beats a lower bound for deterministic on-line algorithms. We consider extensions to the case of parallel machine scheduling, and for this we introduce two new ideas: first, we show that a preemptive one-machine relaxation is a powerful tool for designing parallel machine scheduling algorithms that simultaneously produce good approximations and have small running times; second, we show that a non-greedy {open_quotes}rounding{close_quotes} of the relaxation yields better approximations than a greedy one. We also prove a general theorem relating the value of one-machine relaxations to that of the schedules obtained for the original m-machine problems. This theorem applies even when there are precedencemore » constraints on the jobs. We apply this result to precedence graphs such as in-trees, out-trees, and series- parallel graphs; these are of particular interest in compiler applications that partly motivated our work.« less