Regulating an M/G/1 queue when customers know their demand

Customers do not necessarily join a queue at a socially optimal rate. Hence, queueing systems may call for regulation. For customers in an M/G/1 unobservable (not necessarily FCFS) queue and homogeneous with respect to waiting costs and service rewards, we show how queueing systems can be regulated by imposing an entry fee, a holding fee (based on time in the system), or a service fee (based on the required service time) when customers know their service requirements. We start with a unified approach and state the socially optimal fees. We show that customers are always worse off under a flat entry fee in comparison with holding and service fees. As for holding vs. service fees, the answer depends on the queueing regime and/or the service length itself. For example, under FCFS, service fees are preferred by all. Details are given on some common service regimes. We also review the case where customers know only the common distribution of service times, but not their actual requirements.     

Reconfigurable Optical Bus and Performance Optimization

With the advent of optical fiber and other advanced technologies in solid state,pipelining signals at the wire(or transmission line)level has becomr possible.This has,in turn,made the slotted bus a potential candidate for interconnection networks(IN)for tightly coupled multiprocessor systems.However,a bus an provide only limited bandwidth.Though slotted bus can provide considerably more bandwith in comparison to the traditional non-slotted bus,it is not enough for fine-grain parallel applications run on the shared-memory systems.One well known method to increase the effective bandwidth of a slotted bus in the LAN/MAN environment is to reuse the bandwwidth by reusing slots.However,in a tightly coupled environment reusing slots is not a lucrative option because the significant buffering needs arising from slot reuse will introduce intolerable delay.In this paper we propose a methodology to reuse part of the bandwith available from temporal and spectral bandwidth expansion with none of minimum buffering delay,resulting in significant performance improvement in both the effective throughput and response time(communication latency).The proposed method entails the design and analysis of a re-configurable bus structure with both temporal and spectral bandwidth expansion and a polynomial time algorithm for optimal configurations for given traffic conditionslWe have compared the performance of our reconfigured bus with that of the traditional slotted bus for uniform and localized traffic pattern and founr that the reconfigured bus outperforms the traditional slotted bus substantially in many practical scenarios.     

Analysis of waiting time of M/G/1/K system with vacations under random scheduling and LCFS

This paper considers an M/G/1/K queueing system with multiple vacations under random scheduling and LCFS disciplines. As for M/G/1/K vacation models, Lee obtained the results of the joint distribution of the number of messages in the system and the remaining service or vacation time for a message. Using these expressions, we derive LSTs of the waiting time distribution under the two service disciplines. We show the calculation method for the first and the second moments of the waiting time under two service disciplines. Furthermore, we illustrate some numerical results of the mean waiting times and the coefficient of variations of the waiting time under FCFS, random scheduling and LCFS.     

Response times in a two-node queueing network with feedback

The study presented in this paper is motivated by the performance analysis of response times in distributed information systems, where transactions are handled by iterative server and database actions. We model system response times as sojourn times in a two-node open queueing network with a processor sharing (PS) node and a first-come-first-served (FCFS) node. External customers arrive at the PS node according to a Poisson process. After departing from the PS node a customer proceeds to the FCFS node with probability p, and with probability 1−p the customer departs from the system. After a visit to the FCFS node, customers are fed back to the PS node. The service requirements at both nodes are exponentially distributed. The model is a Jackson network, admitting a product-from solution for the joint number of customers at the nodes, immediately leading to a closed-form expression for the mean sojourn times in steady-state. The variance of the sojourn times, however, does not admit an exact expression—the complexity is caused by the possibility of overtaking. In this paper we propose a methodology for deriving simple, explicit and fast-to-evaluate approximations for the variance of the sojourn times. Numerical results demonstrate that the approximations are very accurate in most model instances.     

An approximate MVA algorithm for exponential, class-dependent multiple servers

Mean value analysis (MVA) is an efficient algorithm for determining the mean sojourn time, the mean queue length, and the throughput in a closed multiclass queueing network. It provides exact results for the class of product-form networks. Often different classes have different service requirements in FCFS queues, but such networks are not of product form. There are several possibilities to compute performance measure for such nodes and networks. In this paper we present an approximation formula for multiple-server FCFS queues with class-dependent service times as a Norton flow equivalent product node, where the departure rate of any class depends on the number of customers of all classes in the queue. We will use this approximation in the sojourn time formula of some exact and approximate MVA algorithms.     

Lead time control in multi-class multi-stage assembly systems with finite capacity

In this paper, we model multi-class multi-stage assembly systems with finite capacity as queueing networks. It is assumed that different classes (types) of products are produced by the production system and products’ orders for different classes are received according to independent Poisson processes. Each service station of the queueing network specifies a manufacturing or assembly operation, in that processing times for different types of products are independent and exponentially distributed random variables with service rates, which are controllable, and the queueing discipline is First Come First Served (FCFS). Different types of products may be different in their routing sequences of manufacturing and assembly operations. For modeling multi-class multi-stage assembly systems, we first consider every class separately and convert the queueing network of each class into an appropriate stochastic network. Then, by using the concept of continuous-time Markov processes, a system of differential equations is created to obtain the distribution function of manufacturing lead time for any type of product, which is actually the time between receiving the order and the delivery of finished product. Furthermore, we develop a multi-objective model with three conflicting objectives to optimally control the service rates, and use goal attainment method to solve a discrete-time approximation of the original multi-objective continuous-time problem.     

Comparative evaluation of contiguous allocation strategies on 3D mesh multicomputers

The performance of contiguous allocation strategies can be significantly affected by the type of the distribution adopted for job execution times. In this paper, the performance of the existing contiguous allocation strategies for 3D mesh multicomputers is re-visited in the context of heavy-tailed distributions (e.g., a Bounded Pareto distribution). The strategies are evaluated and compared using simulation experiments for both First-Come-First-Served (FCFS) and Shortest-Service-Demand (SSD) scheduling strategies under a variety of system loads and system sizes. The results show that the performance of the allocation strategies degrades considerably when job execution times follow a heavy-tailed distribution. Moreover, SSD copes much better than FCFS scheduling strategy in the presence of heavy-tailed job execution times. The results also reveal that allocation strategies that employ a list of allocated sub-meshes for both allocation and de-allocation exhibit low allocation overhead, and maintain good system performance in terms of average turnaround time and mean system utilization.     

Approximate analysis of reader/writer queues

We analyze the performance of queues that serve readers and writers. Readers are served concurrently, while writers require exclusive service. We approximately analyze a first-come-first-serve (FCFS) reader/writer queue, and derive simple formulae for computing waiting times and capacity under the assumption of Poisson arrivals and exponential service. We extend the analysis to handle a one writer queue, and a queue that includes write intention locks. The simple analyses that we present can be used as rules of thumb for designing concurrent systems     

Due-date assignment for multi-server multi-stage assembly systems

In this paper, we attempt to present a constant due-date assignment policy in a multi-server multi-stage assembly system. This system is modelled as a queuing network, where new product orders are entered into the system according to a Poisson process. It is assumed that only one type of product is produced by the production system and multi-servers can be settled in each service station. Each operation of every work is operated at a devoted service station with only one of the servers located at a node of the network based on first come, first served (FCFS) discipline, while the processing times are independent random variables with exponential distributions. It is also assumed that the transport times between each pair of service stations are independent random variables with generalised Erlang distributions. Each product's end result has a penalty cost that is some linear function of its due date and its actual lead time. The due date is calculated by adding a constant to the time that the order enters into the system. Indeed, this constant value is decided at the beginning of the time horizon and is the constant lead time that a product might expect between the time of placing the order and the time of delivery. For computing the due date, we first convert the queuing network into a stochastic network with exponentially distributed arc lengths. Then, by constructing an appropriate finite-state continuous-time Markov model, a system of differential equations is created to find the manufacturing lead-time distribution for any particular product, analytically. Finally, the constant due date for delivery time is obtained by using a linear function of its due date and minimising the expected aggregate cost per product.     

双头镜像磁盘的SSTF调度算法

首先简要介绍了双头镜像磁盘系统的研究现状,然后针对双头镜像磁盘系统中传统的先来先服务（ＦＣＦＳ）调度算法提出一种新的调度算法：短寻道时间优先算法（Ｓｈｏｒｔ Ｓｕｅｅｋ－Ｔｉｍｅ Ｆｉｒｓｔ－ＳＳＴＦ）。根据蒙特卡罗模拟实验方法,对双头镜像磁盘系统下的这两种调度算法进行模拟,从模拟实验的结果中定量分析出ＳＳＴＦ调 度算法大大提高了系统的性能。本文还讨论了在该调度算法下,系统的平均寻道时间与Ｉ／Ｏ请     

Asymptotic analysis of a heterogeneous multiprocessor system in arandomly changing environment

An asymptotic queuing theoretic approach is proposed to analyze the performance of an FCFS (first-come, first-served) heterogeneous multiprocessor computer system with a single bus operating in a randomly changing environment. All stochastic times in the system are considered to be exponentially distributed and independent of the random environment, while the access and service rates of the processors are subject to random fluctuations. It is shown under the assumption of `fast' arrivals that the busy period length of the bus converges weakly, under appropriate normalization, to an exponentially distributed random variable. As a consequence, main steady-state performance measures such as system throughput, mean delay time, expected waiting time, and mean number of active processors can be approximately determined. The reliability of the proposed method is validated by comparing the new approximations with known exact results     

分布式存储系统读写一致性算法性能优化研究综述

读写一致性算法被广泛部署到分布式存储系统,以保证读写数据的正确性。然而,读写一致性算法通常需要使用一个复杂的通信协议来保证多个节点读写数据的正确性,会带来较大网络传输开销和读写时延。由于各种读写一致性算法实现机制存在较大差异,特定的读写一致性算法往往需要部署到特定的存储应用场景,才能高效地执行数据读写操作,保障对其上应用的服务质量。因此,实际的存储系统开发过程中,开发人员往往需要根据存储应用场景选择读写一致性算法,从而减少数据读写操作带来的系统开销。为了明确各种读写一致性算法适合的应用场景,介绍了分布式存储系统中存在的读写一致性问题,并综述了当前读写一致性算法的实现机制。总结了在副本和纠删码2种存储机制下主流的读写一致性算法,比较了这些读写一致性算法在实现机制、网络开销和数据存储开销等方面的特性。在此基础上,结合了单数据中心分布式存储系统和跨数据中心云际存储系统2种经典的应用场景,总结了开发人员在实际存储系统中部署读写一致性算法过程中需要注意的要点,分析了亟需解决的问题和提升数据读写操作性能的可能途径,展望了读写一致性算法未来的发展方向。     

短事务、强实时双机容错系统的研究

在军事、工业控制以及电子商务系统中存在着大量的高可用,短事务、强实时应用,在这些应用中,采用双机系统具有较高的性能价格比,如何保证双机系统的强实时性,高可用度和服务“不断流”,是其中的关键技术难题,文中着重论述了系统可用度,故障检测,结果判别和状态切换中的关键问题,在理论的指导下,给出上实现策略和实际测试数据,测试数据表明本方案完全满足系统的要求,并且在具体工程实践中得到了应用,取得了明显的效果。     

A probabilistic approach to estimate the mean waiting times in the earliest deadline first polling

In queueing system, the mean waiting times of messages are important measures to characterize the quality of service (QoS) under various requirements. In a time-critical system, message transactions which cannot meet deadline constraints might lead to catastrophic consequences. Currently, the waiting time estimations using the first-come-first-served (FCFS) and priority (PRI) strategies are already well developed. However, in the case of multi-queue dynamic environments, these quantities are more difficult to analyze due to multiple classes of messages are considered. In this paper, we aim to consider a polling system consisting of a number of parallel infinite-capacity single-server queues. We propose a probabilistic approach to derive the waiting times for different classes of messages by using non-preemptive earliest deadline first (EDF) polling policy. The resulting formula can also lead to the FCFS polling and PRI polling by altering the relative deadlines. Moreover, the bounds of waiting times are discussed. The accuracy of the proposed algorithm is established by comparisons with simulation results. The runtime results are in very good convergence with the theoretical predictions made by our formulas, in terms of prediction accuracies of waiting times and untimely service ratios of messages under various scenarios and timing constraints.     

轮转调度算法在Web Services事务流处理中的应用

概括了Web Services及其主要实现技术,具体分析了Web Services事务流处理中现在常用的FCFS技术,并对采用这种技术时由于对服务类型不加区分、对不同事务不分轻重缓急统一处理,而造成服务效率不高、服务质量不好的问题进行了探讨。并且提出了用轮转调度算法来解决该问题的想法,并将FCFS与轮转调度算法的性能进行了比较,进而证明了用轮转调度算法来解决Web Services事务流处理中服务质量不好问题的有效性。     

Evaluation of a CPU Scheduling Mechanism for Multimedia Systems

Multimedia applications handling audio and video data have to obey time characteristics of these media types. Besides a basic functionality to express time relations, correctness with respect to time constraints requires mechanisms which lead to favoured processing of multimedia operations. CPU scheduling techniques based on the experience from real-time operating systems offer a solution and provide multimedia applications with the ability to meet time-related quality of service requirements. This paper discusses mechanisms to express time in multimedia systems and describes an implementation of a CPU scheduler designed to run under IBM's UNIX derivate AIX. The evaluation of the implementation based on measurements shows that the scheduler is able to support the time requirements of multimedia applications and that such mechanisms are indeed necessary since otherwise deadline violations occur.     

Job scheduling in mesh multicomputers

A new approach for dynamic job scheduling in mesh-connected multiprocessor systems, which supports a multiuser environment, is proposed in this paper. Our approach combines a submesh reservation policy with a priority-based scheduling policy to obtain high performance in terms of high throughput, high utilization, and low turn-around times for jobs. This high performance is achieved at the expense of scheduling jobs in a strictly fair, FCFS fashion; in fact, the algorithm is parameterized to allow trade-offs between performance and (short-term) POPS fairness. The proposed scheduler can be used with any submesh allocation policy. A fast and efficient implementation of the proposed scheduler has also been presented. The performance of the proposed scheme has been compared with the FCFS policy, the only existing scheduling strategy for meshes, to demonstrate the effectiveness of the proposed approach. Simulation results indicate that our scheduling strategy outperforms the FCFS policy significantly. Specifically, our strategy significantly reduces the average waiting delay of jobs over the FCFS policy. The fast implementation of the proposed scheduler results in low allocation and deallocation time overhead, as well as low space overhead     

A Non-Forced-Write Atomic Commit Protocol for Cluster File Systems

Distributed metadata consistency is one of the critical issues of metadata clusters in distributed file systems. Existing methods to maintain metadata consistency generally need several log forced write operations. Since synchronous disk IO is very inefficient, the average response time of metadata operations is greatly increased. In this paper, an asynchronous atomic commit protocol （ACP） named Dual-Log （DL） is presented. It does not need any log forced write operations. Optimizing for distributed metadata operations involving only two metadata servers, DL mutually records the redo log in counterpart metadata servers by transferring through the low latency network. A crashed metadata server can redo the metadata operation with the redundant redo log. Since the latency of the network is much lower than the latency of disk IO, DL can improve the performance of distributed metadata service significantly. The prototype of DL is implemented based on local journal. The performance is tested by comparing with two widely used protocols, EP and S2PC-MP, and the results show that the average response time of distributed metadata operations is reduced by about 40%-60%, and the recovery time is only I second under 10 thousands uncompleted distributed metadata operations.     

优先权排队在消防物联网中的应用

针对消防物联网系统中消防监控中心收到的火警信息存在延迟,可能导致救火作战时机延误的问题,提出了一种火警信息优先传输的解决方案。首先,推导出FCFS的M/M/1排队系统的运行指标;其次,将消防报警信息分为火警报警信息、火警消除信息、故障报警信息和故障消除信息等四个优先级,建立非抢占优先权排队系统,并推导出各个优先级的运行指标;最后,从平均逗留时间和平均队长两个维度,比较了非抢占优先权排队系统和M/M/1系统的性能。提出的火警信息优先传输方案,满足了火警信息时延小的要求,同时实现复杂度低,为消防物联网安全信息数据的获取提供一定的理论支撑。     

A prediction-based dynamic file assignment strategy for parallel file systems

Nowadays, the rapid development of the internet calls for a high performance file system, and a lot of efforts have already been devoted to the issue of assigning nonpartitioned files in a parallel file system with the aim of pursuing a prompt response to requests. Yet most of the existing strategies still fail to bring about an optimal performance on system mean response time metrics, and new strategies which can achieve better performance in terms of mean response time become indispensable for parallel file systems. This paper, while addressing the issue of assigning nonpartitioned files in parallel file systems where the file accesses exhibit Poisson arrival rates and fixed service times, presents an on-line file assignment strategy, named prediction-based dynamic file assignment (PDFA), to minimize the mean response time among disks under different workload conditions, and a comparison of the PDFA with the well-known file assignment algorithms, such as HP and SOR. Comprehensive experimental results show that PDFA is able to improve the performance consistently in terms of mean response time among all algorithms for comparison.