NFRL:一种分布系统的实时容错调度算法

在硬实时系统的应用中,如果硬实时任务不能在规定的时限完成,将会产生人员伤亡, 失等严重后果,为了保证在系统出错的情况下,硬实时任务仍然在能戴止时限之前完成,必须研究实时容错技术。本文从实时容错调度算法的角度出发,提出一种基于分布式系统的实时容错调度算法,并研究了该算法的时间复杂度,同时给出一个实例说明该容错调度算法的调度过程。这种容错调算法称为“无容错需求后调度算法（ＮＦＲＬ）,该实时容错调度算法     

容错型令牌总线网性能估计算法

容错型令牌总线网性能估计算法李忠勇，李人厚（西安交通大学自动化系西安７１００４９）ＡＰＥＲＦＯＲＭＡＮＣＥＥＶＡＬＵＡＴＩＯＮＡＬＧＯＲＩＴＨＭＯＦＦＡＵＬＴ－ＴＯＬＥＲＡＮＴＴＯＫＥＮＢＵＳＮＥＴＷＯＲＫ￥ＬｉＺｈｏｎｇｙｏｎｇａｎｄＬｉＲｅｎｈｏ...     

混合型实时容错调度算法的设计和性能分析

以往文献中研究的实时容错调度算法都只能调度单一的具有容错需求的任务.该文建立了一个混合型实时容错调度模型,提出一种静态实时容错调度算法.该算法能同时调度具有容错需求的实时任务和无容错需求的实时任务.该文还提出了一个求解最小处理机个数的算法,用于对静态实时容错调度算法的性能进行模拟分析.为了提高静态调度算法的调度性能,提出了一种动态调度算法.最后,通过模拟实验分析了静态和动态调度算法的性能.实验表明,调度算法的性能与实时任务的个数、任务的计算时间、周期和处理机个数等系统参数相关.     

多机相关任务的均衡调度算法

多机相关任务的均衡调度算法许日滨（青岛大学计算机科学系青岛２６６０７１）ＴＨＥＥＱＵＩＬＩＢＲＩＵＭＳＣＨＥＤＵＬＩＮＧＡＬＧＯＲＩＴＨＭＦＯＲＤＥＰＥＮＤＥＮＴＴＡＳＫＳＩＮＭＵＬＴＩＰＲＯＣＥＳＳＯＲＳ￥ＸｕＹｕｅｂｉｎ（ＤｅｐａｒｔｍｅａｔＣｍ...     

用任意一个基求可行基与基本可行解的算法

用任意一个基求可行基与基本可行解的算法陈开周，郭强（西安电子科技大学）ＡＮＡＬＧＯＲＩＴＨＭＯＦＦＩＮＤＩＮＧＡＦＥＡＳＩＢＬＥＢＡＳＩＳＡＮＤＡＢＡＳＩＣＦＥＡＳＩＢＬＥＳＯＬＵＴＩＯＮＷｆＴＨＡＮＹＢＡＳＩＳ￥ＣｈｅｎＫａｉｚｈｏｕ；ＧｕｏＱｉａ...     

解大型稀疏线性代数方程组的预条件Krylov子空间方法

解大型稀疏线性代数方程组的预条件Ｋｒｙｌｏｖ子空间方法邓健新（中国科学院计算中心）ＰＲＥＣＯＮＤＩＴＩＯＮＩＮＧＫＲＹＬＯＶＳＵＢＳＰＡＣＥＭＥＴＨＯＤＳＦＯＲＬＡＲＧＥＳＰＡＲＳＥＬＩＮＥＡＲＡＬＧＥＢＲＡＩＣＳＹＳＴＥＭＳ￥ＤｅｎｇＪｉａｎ－ｘｉ...     

基于异构分布式系统的实时容错调度算法

目前文献中研究的实时容错调度算法都是基于同构分布式系统，系统中的所有处理机完全相同。该文首先建立了一个基于异构分布式系统实时容错调度模型，异构分布式系统中的各个处理机均不相同。基于该异构分布式系统模型，该文引入了可靠性代价（reliability cost）概念，并提出两种静态实时容错调度算法（RTFTNO和RTFTRC）用于调度周期性实时容错任务。算法RTFTRC在调度任务时，尽量使系统的可靠性代价最小；而算法RTFTNO在调度实时任务时，没有考虑系统的可靠性代价。该文详细讨论了两种调度算法的性能。性能模拟实验分别比较了两个算法的可靠性代价，超时比率和可调度性；并研究了任务的计算时间与可靠性代价的关系以及调度长度阈值与最小处理机个数的关系。实验结果表明，算法RTFTRC的性能优于算法RTFTNO。     

解非线性最小二乘的并行连续极小化算法及其数值试验

解非线性最小二乘的并行连续极小化算法及其数值试验李庆扬，朱鹏（清华大学）ＡＰＡＲＡＬＬＥＬＣＯＮＴＩＮＵＯＵＳＭＩＮＩＭＩＺＡＴＩＯＮＡＬＧＯＲＩＴＨＭＦＯＲＳＯＬＶＩＮＧＮＯＮＬＩＮＥＡＲＬＥＡＳＴ－ＳＱＵＡＲＥＳＰＲＯＢＬＥＭＳＡＮＤＮＵＭＥＲＩ...     

求多总线系统容错度的多项式时间算法

求多总线系统容错度的多项式时间算法陈四清，周六丁（重庆大学计算机科学系重庆６３００４４）ＰＯＬＹＮＯＭＩＡＬ－ＴＩＭＥＡＬＧＯＲＩＴＨＭＳＦＯＲＤＥＴＥＲＭＩＮＡＴＩＮＧＴＨＥＦＡＵＬＴ－ＴＯＬＥＲＡＮＣＥＤＥＧＲＥＥＯＦＭＵＬＴＩＢＵＳＳＹＳＴＥＭ...     

统计数据凑整问题的网络流算法

统计数据凑整问题的网络流算法金大勇，杨承恩（长沙铁道学院）ＮＥＴＷＯＲＫＡＬＧＯＲＩＴＨＭＳＦＯＲＴＨＥＤＡＴＡＲＯＵＮＤＩＮＧＰＲＯＢＬＥＭ￥ＪｉｎＤａ－ｙｏｎｇ；ＹａｎｇＣｈｅｎｇ－ｅｎ（ＣｈａｎｇｓｈａＲａｉｌｗａｙＩｎｓｔｉｔｕｔｅ）Ａｂｓｔ...     

基于动态备份的容错网格任务调度*

提出了一种基于自适应备份的网格容错任务调度算法:最高百分之k备份算法.该算法对任务的安全需求和资源的信任等级进行匹配,在系统安全等级较低并且网络和主机可能失效的网格环境中进行容错任务调度.调度时,该算法根据整个网格系统的安全状况,对具有最高安全需求的百分之k的任务进行动态备份,任务备份数根据系统安全状况自适应变化,并对失败的任务重新调度.仿真结果表明,该算法可以有效提高不安全网格环境下的任务调度成功率,具有很好的容错性和可扩展性,优于固定备份数的网格任务调度算法.     

软件容错模型中的容错实时调度算法

在软件容错模型的容错实时调度算法中,主部分可执行性的预测精度是影响调度算法性能的关键.针对此问题提出了DPA(deep-prediction based algorithm)和EDPA(EDF-based DPA)算法.算法考虑当前时间至替代部分通知时间之间的任务执行情况,通过构建预测表对待执行主部分的可执行性进行精确预测.当主部分不发生错误时算法根据预测表调度任务. DPA依照预测表中通知时间的先后顺序调度主部分,而EDPA则按照EDF算法调度预测表中的主部分.模拟结果表明,DPA和EDPA较目前同类算法可获得更多的主部分执行时间,降低CPU的消耗.当软件错误率较低、任务周期较短时,算法能够以较小的调度开销获得较高的调度性能.     

Real-Time Atomic Multicast Algorithms Implemented on a Shared Memory Multiprocessor

Processes are distributed over processors that share directly accessible memory. Processes exchange messages via memory. Algorithms are specified which satisfy the atomic multicast requirements under two fault hypotheses: (1) fail-stop memory and fail stop processes and (2) fail-stop memory and processes with timing failures. It is shown that the algorithms can be applied under different scheduling conditions: (1) hard real-time (HRT) applications composed of periodically scheduled tasks and (2) HRT applications with tasks scheduled according to a static off-line calculated schedule. The performance measurements on an implementation of two algorithms are presented.     

异构分布式实时系统中对具有前后依赖关系任务的基于动态可变调度距离容错调度算法

目前的主副版本容错调度算法大多没有考虑任务间的前后依赖关系,但实际中很多任务是具有前后依赖关系的。本文提出了一种基于主副版本动态可变调度距离的任务容错调度算法,该技术通过比较任务间的最晚开始执行时间与最早开始执行时间的差值,安排任务副版本的调度,并且基于此设计了可用于具有前后依赖关系任务调度可重叠技术。本文提出的基于动态可变调度距离的容错调度算法在尽可能让任务最早完成的情况下,提高系统的可靠性,并且优先调度关键路径任务,降低了系统的容错开销。最后通过实验证明本文算法的有效性和优异性。     

副版本不可抢占的全局容错调度算法

容错是硬实时系统的关键能力,容错调度算法可以在有错误发生的情况下满足任务的实时性需求.在主副版本机制的容错调度算法中,主版本出错后留给副版本运行的时间窗口小,副版本容易错失截止期.针对副版本需要快速响应的问题,提出副版本不可抢占的全局容错调度算法FTGS-NPB（fault-tolerant global scheduling with non-preemptive backups）,赋予副版本全局最高优先级,使副版本在主版本出错后可以立刻获得处理器资源,并且在运行过程中不会被其他任务抢占.这样,副版本可以在最短时间内响应.分别基于截止期分析和响应时间分析建立了FTGS-NPB的可调度性测试,并分析了两种可调度性测试分别适用于不同的优先级分配算法.仿真实验结果表明,FTGS-NPB可以有效地减少实现容错的代价.     

DAGMap: efficient and dependable scheduling of DAG workflow job in Grid

DAG has been extensively used in Grid workflow modeling. Since Grid resources tend to be heterogeneous and dynamic, efficient and dependable workflow job scheduling becomes essential. It poses great challenges to achieve minimum job accomplishing time and high resource utilization efficiency, while providing fault tolerance. Based on list scheduling and group scheduling, in this paper, we propose a novel scheduling heuristic called DAGMap. DAGMap consists of two phases, namely Static Mapping and Dependable Execution. Four salient features of DAGMap are: (1) Task grouping is based on dependency relationships and task upward priority; (2) Critical tasks are scheduled first; (3) Min-Min and Max-Min selective scheduling are used for independent tasks; and (4) Checkpoint server with cooperative checkpointing is designed for dependable execution. The experimental results show that DAGMap can achieve better performance than other previous algorithms in terms of speedup, efficiency, and dependability.     

Fault-tolerance through scheduling of aperiodic tasks in hardreal-time multiprocessor systems

Real time systems are being increasingly used in several applications which are time critical in nature. Fault tolerance is an important requirement of such systems, due to the catastrophic consequences of not tolerating faults. We study a scheme that provides fault tolerance through scheduling in real time multiprocessor systems. We schedule multiple copies of dynamic, aperiodic, nonpreemptive tasks in the system, and use two techniques that we call deallocation and overloading to achieve high acceptance ratio (percentage of arriving tasks scheduled by the system). The paper compares the performance of our scheme with that of other fault tolerant scheduling schemes, and determines how much each of deallocation and overloading affects the acceptance ratio of tasks. The paper also provides a technique that can help real time system designers determine the number of processors required to provide fault tolerance in dynamic systems. Lastly, a formal model is developed for the analysis of systems with uniform tasks     

New Algorithms for Resource Reclaiming from Precedence Constrained Tasks in Multiprocessor Real-Time Systems

The scheduling of tasks in multiprocessor real-time systems has attracted many researchers in the recent past. Tasks in these systems have deadlines to be met, and most of the real-time scheduling algorithms use worst case computation times to schedule these tasks. Many resources will be left unused if the tasks are dispatched purely based on the schedule produced by these scheduling algorithms, since most of the tasks will take less time to execute than their respective worst case computation times. Resource reclaiming refers to the problem of reclaiming the resources left unused by a real-time task when it takes less time to execute than its worst case computation time. In this paper, we propose two algorithms to reclaim these resources from real-time tasks that are constrained by precedence relations and resource requirements, in shared memory multiprocessor systems. We introduce a notion called a restriction vector for each task which captures its resource and precedence constraints with other tasks. This will help not only in the efficient implementation of the algorithms, but also in obtaining an improvement in performance over the reclaiming algorithms proposed in earlier work [[2]]. We compare our resource reclaiming algorithms with the earlier algorithms and, by experimental studies, show that they reclaim more resources, thereby increasing the guarantee ratio (the ratio of the number of tasks guaranteed to meet their deadlines to the number of tasks that have arrived), which is the basic requirement of any resource reclaiming algorithm. From our simulation studies, we demonstrate that complex reclaiming algorithms with high reclaiming overheads do not lead to an improvement in the guarantee ratio.     

异构分布式系统混合型实时容错调度算法

基/副版本技术是实现实时分布式系统容错的一个重要手段。提出了一种异构分布式混合型容错模型,该模型与传统的异构分布式实时调度模型相比同时考虑了周期和非周期调度任务。在此基础上给出3种容错调度算法:以可调度性为目的SSA算法、以可靠性为目的RSA算法、以负载均衡性为目的BSA算法。算法能够在异构系统中同时调度具有周期和非周期容错需求的实时任务,且能够保证在异构系统中某节点机失效情况下,实时任务仍然能在截止时间内完成。最后从可调度性、可靠性代价、负载均衡性、周期与非周期任务数及任务周期与粒度J个方面对算法进行了分析。模拟实验结果显示算法各有优缺点,所以在选择调度算法时应该根据异构系统的特点来选择。