一种基于平均寻道时间的磁盘调度优化算法

针对如何提高磁盘调度效率的问题,提出了一种基于平均寻道时间(AST)的磁盘调度优化算法。对操作系统中几种主要磁盘调度算法的平均寻道时间作深入研究,随机选取几组磁盘服务请求队列,分析在每种算法下磁头移动情况。然后通过模拟和解析,得到不同调度算法的平均寻道时间的摆动规律,进而提出一种基于平均寻道时间的磁盘调度优化算法,使得系统能够在不同的情况下实时地自动选择已有的算法来提高磁盘调度的效率。     

并发定位的双头镜像磁盘的调度算法

本文建立了双头镜像磁盘系统的模型，提出双头镜像磁盘系统中并发定位操作的思想，然后给出并发定位磁盘调度算法。在阐述了模拟模型后，对并发定位调度算法及串行定位调度算法进行了性能模拟。从模拟结果中定量分析出并发定位调度的性能优于串行定位调度，并发定位调度算法使系统性能有很大的提高。文献［５］认为系统的寻道时间不受Ｉ／Ｏ请求到达率λ的影响，但本文的实验表明，采用了并发调度算法，Ｉ／Ｏ请求到达率λ与系统寻道     

Linux I/O调度算法分析与研究

研究表明,好的磁盘调度算法可以明显优化磁盘的I/O性能,Linux提供四种调度算法可供选择。基于Linux 2.6.32内核源码,研究Noop、Deadline、Anticipatory、CFQ四种磁盘调度算法的基本原理和特点,分析每种算法的优缺点,这对系统管理员针对不同类型的应用场景来调整优化I/O调度算法有着重要意义。     

智能网络磁盘调度算法

针对当前网络存储系统中存在的问题，提出了基于智能算法的智能网络磁盘IND的存储方案，探讨了IND系统的结构，设计了相应的应用协议，实现了智能网络磁盘调度算法。通过应用协议实现了对外虚拟存储，并将文件服务器分放到智能磁盘，避免了单点故障和性能瓶颈。通过对多个磁盘的并行调度算法，实现了并行传输，提高了文件的传输速度。以此为基础，设计和实现了IND模拟程序。试验结果显示，智能网络磁盘有助于避免单点故障，提高数据文件的传输效率。     

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     

连续媒体服务的磁盘调度算法—EDLSF

主要对连续媒体服务中I／O子系统的磁盘调度问题进行讨论。提出了一种新的调度算法－EDLSF（Earliest Deadine and Least Seek First)来解决连续媒体的访问。EDLSF算法综合考虑了磁盘服务时间和实时特点,通过分析、比较EDLISF算法和其它调度算法在提供并发访问数量上的多少,说明EDLSF算法是能够较好处理连续媒体请求的算法。     

一种基于数据划分的字符串相似连接外存算法

字符串相似连接操作具有广泛应用,因而将着重研究基于编辑距离的字符串相似连接.而现有的字符串相似连接算法大多为内存算法.实际应用中的数据集越来越大,有必要针对超大规模数据集研制字符串相似性连接外存算法.利用组合频率向量划分数据集,并提出了基于编辑距离的字符串相似性连接外存算法框架,证明了磁盘调度问题的难度并提出了不同的启发式磁盘调度方法.此外,还提出了基于该外存算法框架实现字符串相似性连接增量式计算的方法.实验结果表明,数据划分方法可以有效地过滤不相关的数据子集;磁盘调度算法能够有效减少磁盘IO次数;外存算法是高效的;增量式计算方法能够高效地处理数据更新.     

VBR视频流磁盘I/O的平滑调度算法

文章将带宽平滑技术引入磁盘 I/ O调度 ,基于现已取得的研究成果 ,考虑磁盘 I/ O存取特性 ,提出一个针对VBR视频检索的整数块平滑调度算法 .算法所得的结果被证明是优化的 ,实验结果显示该算法在磁盘空间和磁盘 I/ O的带宽利用方面有很好的性能     

双头镜橡磁盘的实时调度算法及性能评价

本文对双头镜像磁盘系统模型进行实时扩展,并提出了三种实时调度算法：最早截止期优先算法（ＥＤＦ）,可满足的最早截止期优先算法（Ｆ－ＥＤＦ）和忽视超时限请求算法（ＩＧＭ－ＥＤＦ）。这三种算法充分考虑了Ｉ／Ｏ请求的截止期限,使双头镜像磁盘系统能更好地满足实时需求,在进行了性能模拟后,发现实时调度算法比非实时算法能更好地满足时Ｉ／Ｏ请求的时限要求。三种实时调度算法中,适用于硬实时应用的ＩＧＭ－ＥＤＦ的性能     

非固定双头镜像磁盘实时调度算法的研究

文章给出一个实时非固定双头镜像磁盘系统的形式化模型.该磁盘模型中的每个双头磁盘都有两个相互独立的磁臂,能够独立地完成寻找磁道过程.针对该磁盘系统,文章研究了3种实时调度算法.模拟实验表明,“忽略超截止期调度算法”的性能最好,因为它忽略了对超截止期限实时请求的处理.文章同时分析了固定双头镜像磁盘与非固定双头镜像磁盘之间的性能差别.实验结果表明,由于非固定双头磁盘的两个磁头可以独立寻找磁道,因此非固定双头镜像磁盘的性能比固定双头镜像磁盘的性能要好.     

Energy-aware disk scheduling for soft real-time I/O requests

In this work, we develop energy-aware disk scheduling algorithm for soft real-time I/O. Energy consumption is one of the major factors which bar the adoption of hard disk in mobile environment. Heat dissipation of large scale storage system also calls for an energy-aware scheduling technique to further increase the storage density. The basic idea in this work is to properly determine the I/O burst size so that device can be in standby mode between consecutive I/O bursts and that it can satisfy the soft real-time requirement. We develop an elaborate model which incorporates the energy consumption characteristics, overhead of mode transition in determining the appropriate I/O burst size and the respective disk operating schedule. Efficacy of energy-aware disk scheduling algorithm greatly relies on not only disk scheduling algorithm itself but also various operating system and device firmware related concerns. It is crucial that the various operating system level and device level features need to be properly addressed within disk scheduling framework. Our energy-aware disk scheduling algorithm successfully addresses a number of outstanding issues. First, we examine the effect of OS and hard disk firmware level prefetch policy and incorporate its effect in our disk scheduling framework. Second, our energy aware scheduling framework can allocate a certain fraction of disk bandwidth to handle sporadically arriving non real-time I/O’s. Third, we examine the relationship between lock granularity of the buffer management and energy consumption. We develop a prototype software with energy-aware scheduling algorithm. In our experiment, proposed algorithm can reduce the energy consumption to one fourth if we use energy-aware disk scheduling algorithm. However, energy-aware disk scheduling algorithm increases buffer requirement significantly, e.g., from 4 to 140 KByte. We carefully argue that the buffer overhead is still justifiable given the cost of DRAM chip and importance of energy management in modern mobile devices. The result of our work not only provides the energy efficient scheduling algorithm but also provides an important guideline in capacity planning of future energy efficient mobile devices. This paper is funded by KOSEF through Statistical Research Paper for Complex System at Seoul National University.     

基于多核ARM的数控系统实时性研究

随着数控系统的不断发展,数控系统对精度和速度有了更高的要求,这都对当前普遍采用的单核处理器平台提出了严峻的挑战.基于同构的四核ARM处理器平台,在添加了实时补丁的Linux系统环境下,根据数控系统中硬实时任务、软实时任务、非实时任务并存的特点,把数控系统任务合理的分配到多核ARM上运行,并采用改进的RM算法进行调度,最后对新的任务调度算法进行实时性能测试.本调度模型能够解决了数控系统混合任务调度的问题,并能满足数控系统对实时性的要求.     

A genetic based disk scheduling method to decrease makespan and missed tasks

Disk scheduling is an operating system process to service disk requests. It has an important role in QOS guarantee of soft real-time environments such as video-on-demand and multimedia servers. Since now, some disk scheduling algorithms have been proposed to schedule disk requests in an optimized manner. Most of these methods try to minimize makespan by decreasing the number of disk head seeks as one of the slowest operations in modern computers and crucial for system performance because it usually takes some milli-seconds. In this paper, we propose a new disk scheduling method based on genetic algorithm that considers makespan and number of missed tasks simultaneously. In the proposed method, a new coding scheme is presented which employs simple GA procedures such as crossover and mutation and a penalty function in fitness. To get the best performance of the proposed method, its parameters such as number of chromosomes in initial population, mutation, and crossover probabilities, etc have been adjusted by applying it on some sample problems. The algorithm has been tested on several problems and its results were compared with well-known related methods. Experimental results showed that the proposed method worked very well and excelled most related works in terms of miss ratio and average seeks.     

Dispatching rule selection using artificial neural networks for dynamic planning and scheduling

To schedule a job shop, the first task is to select an appropriate scheduling algorithm or rule. Because of the complexity of scheduling problems, no general algorithm sufficient for solving all scheduling problems has yet been developed. Most job-shop scheduling systems offer alternative algorithms for different situations, and experienced human schedulers are needed to select the best dispatching rule in these systems. This paper proposes a new algorithm for job-shop scheduling problems. This algorithm consists of three stages. First, computer simulation techniques are used to evaluate the efficiency of heuristic rules in different scheduling situations. Second, the simulation results are used to train a neural network in order to capture the knowledge which can be used to select the most efficient heuristic rule for each scheduling situation. Finally, the trained neural network is used as a dispatching rule selector in the real-time scheduling process. Research results have shown great potential in using a neural network to replace human schedulers in selecting an appropriate approach for real-time scheduling. This research is part of an ongoing project of developing a real-time planning and scheduling system.     

一种新的组优先级动态实时调度算法

传统动态调度算法由于对优先级个数没有限制,在实际应用中往往受制约,达不到很好的调度性能.针对此问题,考虑硬实时抢占任务调度需要,提出一种新的组优先级动态实时调度算法.研究作业执行顺序改变对系统可调度性能的影响,给出作业分组可调度性能测试.新算法将满足分组可调度测试公式的作业作为一个任务组,各任务组之间按照最小截止期优先调度,任务组内按照最短作业优先的原则执行作业.仿真结果表明,与最小截止期优先等传统调度算法相比,新算法不仅能有效降低算法所需优先级个数,还能提高任务调度的成功率,缩短平均响应时间,减少任务切换次数.     

嵌入式Forth操作系统实时调度算法研究

针对目前嵌入式Forth操作系统中缺乏实时调度机制的问题,对基于Forth虚拟机架构的嵌入式操作系统中多任务调度的关键技术进行了研究。采用Forth虚拟机技术,新定义了一种中断任务类型来处理实时突发事件,并给出了一种新的任务调度算法来调度 Forth系统中终端任务、后台任务以及中断任务顺利运行。实验结果表明,改进后的 Forth 系统能够通过实时调度处理突发事件,并且实时响应度高,尤其适用于对实时性有要求的嵌入式环境中,以满足日趋复杂的嵌入式环境对高效操作系统和 Forth 技术的应用需求。     

一种支持实时集群系统的双层调度机制

提出一种集群环境下的实时调度机制,它通过前端负载机平衡调度、后端机区分实时和非实时任务队长差调度而提供实时优先服务,有效提高了以往前端机单点调度模式下的集群节点利用率和实时任务响应性.对比实验表明,在保证吞吐率的情况下,实时任务的响应时间明显减少,为分布式实时调度提供了一种可行的设计参考.     

Message scheduling for real-time interprocessor communication

In this paper an efficient algorithm is proposed which optimizes periodic message scheduling in a real-time multiprocessor system. The system is based on a many-core single-chip computer architecture and uses a multistage baseline network for inter-core communication. Due to its basic architecture, internal blockings can occur during data transfers, i.e. the baseline network is not real-time capable by itself. Therefore, we propose a scheduling algorithm that may be performed before the execution of an application in order to compute a non-blocking schedule of periodic message transfers. Additionally, we optimize the clock rate of the network subject to the constraint that all data transfers can be performed in a non-blocking way. Our solution algorithm is based on a generalized graph coloring model and a randomized greedy approach. The algorithm was tested on some realistic communication scenarios as they appear in modern electronic car units. Computational results show the effectiveness of the proposed algorithm.     

控制系统中强实时任务的调度

文章通过对控制系统中强实时任务进行分析,指出系统存在的各类强实时任务。针对控制系统中任务的特点,提出了一种实时任务调度方法。对这种调度算法进行了可调度性分析,指出实时控制系统中任务可调度的条件。     

基于RM与EDF的实时混合调度算法研究

通过对实时系统中静态调度算法RM和动态调度算法EDF的研究与分析,针对两种调度算法在实际应用中的问题,提出了一种基于阈值δ的混合调度算法,将RM与EDF调度算法相结合,并从数学角度描述了混合调度算法的可调度性与实时任务的周期、执行时间等属性之间的关系,给出了混合调度算法可调度性的充分必要条件。最后用实验验证了混合调度算法的有效性。