实时多处理机系统BEST-FIT启发式容错调度

本文从有效利用资源的角度出发,提出了一种以最小化处理机数目为优化目标的Best-Fit启发式容错调度算法。该算法采用主/副版本备份技术和副版本的主动运行方式与被运行方式相结合的方法,将实时任务的主版本和副版本调度到不同处理机上运行;并且按照Best-Fit启发式策略为实时任务主版本寻找“最佳满足”处理机,使尽可能多的实时任务副版本以被动方式运行。算法既保证了系统的实时性和容错性,也节约了处理机。分析和仿真结果均证明了算法的有效性。     

基于多处理机的混合实时任务容错调度

提出了一种混合实时任务容错调度算法．该算法采用Rate Monotonic(RM)算法完成周期任务的静态调度；采用预订处理机时间方法和Earlier Deadline First(EDF)算法动态调度非周期任务；采用主／副版本备份技术确保系统的容错能力．通过充分利用周期任务的剩余处理机时间调度非周期任务和主动备份与被动备份相结合的方法有效地减少了处理机数．仿真结果证明了算法的有效性．     

异构分布式系统中一种新型主副版本调度算法

针对异构分布式系统中处理器数量相对较少时优先级约束条件带来的副版本调度易失败问题，提出一种新型高可靠性主副版本调度算法（HRPB）。任务模型以有向无环图（DAG）表示，该算法共计调度主、副两个版本的任务。在任务优先级排序阶段，根据任务执行时间及截止时限来制定新指标平均最晚开始时间（ALST）进行排序；在任务处理器分配阶段，采取多一重备份策略以解决处理器数量相对较少时优先级约束条件带来的副版本调度易失败问题，并且改进了副版本调度时的可靠性指标计算方法。通过随机生成DAG图进行算法仿真测试，实验结果表明，HRPB比eFRD具有更优的副版本调度成功率、更高的系统可靠性。     

分布式控制系统中多种混合任务的容错调度

分布式控制系统中存在有强实时、软实时和非实时等多种实时性的任务,其中强实时任务必须在其时限前完成,否则会出现灾难性后果,因此必须为分布式控制系统提供一定的容错能力。首先给出了用于调度多种实时性任务的单处理器调度算法——双优先级队列调度算法,并分析算法的可调度性条件。针对分布式控制系统,考虑基版本与副版本的执行时间不同时,结合版本复制技术和单处理器调度算法提出了一种新的容错调度算法。分析了算法的可调度行,给出了可任务集的可调度条件判断方法和基版本任务时限的设置方法。在此基础上,采用启发式静态任务分配算法,保证各处理器的负载均衡。本算法在保证任务容错可调度的条件下,可提高系统中各处理器的利用率,仿真结果表明该算法是有效的。     

基于模拟退火算法的改进主/副版本调度算法

针对异构分布式系统中面向任务优先级约束的调度问题,提出一种基于模拟退火算法的改进主/副版本调度算法SAPB。任务模型以有向无环图DAG表示,该算法共计调度主、副2个版本的任务。在任务优先级排序阶段,采取HEFT的任务排序方法,避免了eFRD等主/副版本调度算法中任务模型描述的局限性问题;在任务处理器分配阶段,采取模拟退火算法搜索满足截止时限条件下具有更高可靠性的调度结果,并且采取多一重备份策略以解决处理器数量相对较少时任务优先级约束带来的副版本调度易失败问题。最后,通过随机生成的DAG图进行仿真实验,结果表明,相比eFRD等算法SAPB具有更优的副版本可调度性和更高的系统可靠性。     

云环境下周期和非周期混合实时任务双容错调度算法

云环境中的处理机故障已成为云计算不可忽视的问题,容错成为设计和发展云计算系统的关键需求。针对一些容错调度算法在任务调度过程中调度效率低下以及任务类型单一的问题,提出一种处理机和任务主副版本分组的容错调度方法;并给出了副版本可重叠执行的判定方法,以及任务最坏响应时间的计算公式。通过实验和分析表明,和以前算法相比,将处理机分成两组分别执行任务主版本和任务副版本,减少了任务调度所需进行可调度测试的时间,增加了副版本重叠执行的机会,减少了所需的处理机个数,对提高系统处理机的利用率和容错调度的效率具有重要的意义。     

容错多处理机中一种高效的实时调度算法

针对基于主副版本容错的多处理机中独立的、抢占性的硬实时任务,提出了一种高效的调度算法——TPFTRM(task partition based fault tolerant rate-monotonic)算法.该算法将单机实时RM 算法扩展到容错多处理机上,并且调度过程中从不使用主动执行的任务副版本,而仅使用被动执行和主副重叠方式执行的任务副版本,从而最大限度地利用副版本重叠和分离技术提高了算法调度性能.此外,TPFTRM 根据任务负载不同将任务集合划分成两个不相交的子集进行分配;还根据处理机调度的任务版本不同,将处理机集合划分成3 个不相交的子集进行调度,从而使TPFTRM 调度算法便于理解、实现以及减少了调度所需要的运行时间.模拟实验对各种具有不同周期和任务负载的任务集合进行了调度测试.实验结果表明,TPFTRM与目前所知同类算法相比,在调度相同参数的任务集合时不仅明显减少了调度所需要的处理机数目,还减少了调度所需要的运行时间,从而证实了TPFTRM 算法的高效性.     

On the design of communication-aware fault-tolerant scheduling algorithms for precedence constrained tasks in grid computing systems with dedicated communication devices

Fault-tolerant scheduling is an imperative step for large-scale computational Grid systems, as often geographically distributed nodes co-operate to execute a task. By and large, primary-backup approach is a common methodology used for fault tolerance wherein each task has a primary and a backup on two different processors. In this paper, we address the problem of how to schedule DAGs in Grids with communication delays so that service failures can be avoided in the presence of processors faults. The challenge is, that as tasks in a DAG have dependence on each other, a task must be scheduled to make sure that it will succeed when any of its predecessors fails due to a processor failure. We first propose a communication model and determine when communications between a backup and backups of its successors are necessary. Then we determine when a backup can start and its eligible processors so as to guarantee that every DAG can complete upon any processor failure. We develop two algorithms to schedule backups, which minimize response time and replication cost, respectively. We also develop a suboptimal algorithm which targets minimizing replication cost while not affecting response time. We conduct extensive simulation experiments to quantify the performance of the proposed algorithms.     

基于超立方体的静态任务调度

该文给出一个基于超立方体的静态任务调度算法.在算法的设计中,首先建立了任务优先级表和处理机优先级表,任务在调度时总是顺次调度高优先级任务,然后再从处理机优先级表中选择能使该任务最早开始执行的处理机.最后,分别给出了基于LU分解的任务图与随机生成的任务图的调度结果.     

基于GA的DCS中任务的容错优化调度

分布式控制系统(DCS)中的实时任务必须在其时限前完成,否则会出现灾难性后果,因此必须为DCS提供一定的容错能力。该文基于EDF算法和版本复制技术给出了DCS的容错调度算法。在此基础上采用启发式任务分配算法分配任务,通过遗传算法对基版本任务时限进行优化,以提高处理器的利用率。仿真结果表明该算法是有效的。     

Increasing processor utilization in hard-real-time systems with checkpoints

Often hard real-time systems require results that are produced on time despite the occurrence of processor failures. This paper considers a distributed system where tasks are periodic and each task occurs in multiple copies which are periodically synchronized in order to handle failures. The problem of preemptively scheduling a set of such tasks is discussed where every occurrence of a task has to be completely executed before the next occurrence of the same task. First, a static scheduling algorithm is proposed which uses periodic checkpoints to tolerate processor failures. Then, the performance of the algorithm is substancially improved employing a mixed strategy which constructs a schedule where high frequency tasks are duplicated, and low frequency tasks are periodically checkpointed. The performance of the solution proposed is evaluated in terms of the minimum achievable processor utilization due to the useful computation of the tasks. Moreover, analytical and simulation studies are used to reveal interesting trade-offs associated with the scheduling algorithm. In particular, if high frequency tasks are less than 70 percent of the total number of tasks then the mixed strategy yields a higher processor utilization than the task duplication scheme.     

Task allocation model for distributed systems

The problem of distributing tasks to processors in a distributed computing system is addressed. A task should be assigned to a processor whose capabilities are most appropriate for the execution of that task and excessive interprocessor communication is avoided. A simple algorithm for task allocation is presented. The execution costs and communication costs of the tasks are represented by arrays. A task is either assigned to a processor or fused with another task using a simple criterion. The execution and communication costs are then modified suitably. The process continues until all the tasks are assigned to processors. This algorithm also facilitates incorporation of various system constraints. It is applicable to random program structures and to a system containing any number of processors.     

一种调度In-Tree任务图的算法

In-Tree任务图可用来表示归并、求和等分治算法的很多问题,该文针对这种任务图提出一种分层调度算法,利用队列存放被调度的任务,在同层任务调度中,优先把前驱不为空的任务调度到其一个前驱处理器上执行,只有前驱为空的任务才考虑是否分配新的处理器。实验表明,与以前的算法相比,该算法在调度长度相当的情况下,使用了更少的处理器。     

Fault-Tolerant Scheduling for Real-Time Embedded Control Systems

With the increasing complexity of industrial application, an embedded control system (ECS) requires processing a number of hard real-time tasks and needs fault-tolerance to assure high reliability. Considering the characteristics of real-time tasks in ECS, an integrated algorithm is proposed to schedule real-time tasks and to guarantee that all real-time tasks are completed before their deadlines even in the presence of faults. Based on the nonpreemptive critical-section protocol (NCSP), this paper analyzes the blocking time introduced by resource conflicts of relevancy tasks in fault-tolerant multiprocessor systems. An extended schedulability condition is presented to check the assignment feasibility of a given task to a processor. A primary/backup approach and on-line replacement of failed processors are used to tolerate processor failures. The analysis reveals that the integrated algorithm bounds the blocking time, requires limited overhead on the number of processors, and still assures good processor utilization. This is also demonstrated by simulation results. Both analysis and simulation show the effectiveness of the proposed algorithm in ECS.     

On exploiting task duplication in parallel program scheduling

One of the main obstacles in obtaining high performance from message-passing multicomputer systems is the inevitable communication overhead which is incurred when tasks executing on different processors exchange data. Given a task graph, duplication-based scheduling can mitigate this overhead by allocating some of the tasks redundantly on more than one processor. In this paper, we focus on the problem of using duplication in static scheduling of task graphs on parallel and distributed systems. We discuss five previously proposed algorithms and examine their merits and demerits. We describe some of the essential principles for exploiting duplication in a more useful manner and, based on these principles, propose an algorithm which outperforms the previous algorithms. The proposed algorithm generates optimal solutions for a number of task graphs. The algorithm assumes an unbounded number of processors. For scheduling on a bounded number of processors, we propose a second algorithm which controls the degree of duplication according to the number of available processors. The proposed algorithms are analytically and experimentally evaluated and are also compared with the previous algorithms     

一种新的异构实时分布式系统的容错调度算法

一般来说,异构分布式实时系统中任务的周期并不完全相同且任务的时限不等于它们的周期,同时系统中还有一些无容错需求的任务.因此现有的任务调度算法一般不能满足这些要求.针对这类系统,在结合基版本/副版本技术和EDF算法的基础上,给出了一种新的容错调度算法.该算法由两部分组成：任务分配调度算法和单处理器调度算法.对于单处理器调度算法,本文采用了EDF算法;在此基础上,给出一种启发式静态任务分配算法.分析了系统的可调度性,给出了任务可调度条件和基版本/副版本时限的设置方法.仿真结果表明,这种算法是有效的.     

基于EDF的分布式控制系统容错调度算法

现有的分布式实时系统的容错调度算法要求系统中所有任务的周期相同且等于其时限,而实际中任务的周期常常是互不相同的.根据控制系统中任务的特点,结合任务分配算法与处理器的调度算法,提出了基于基版本/副版本技术和EDF算法的容错调度算法.该算法不要求任务的周期都相同,并通过设置基版本/副版本任务时限控制它们的执行时间不重叠,给出了基版本/副版本任务时限的设置方法,并对任务集的可调度性进行了分析.当任务集可调度时,给出其最大利用率和最小处理器个数的约束条件.最后给出一个仿真实例,结果表明了算法的有效性.     

基于动态关键任务的多处理器任务分配算法

多处理器调度问题是影响系统性能的关键问题,基于任务复制的调度算法是解决多处理器调度问题较为有效的方法.文中分析了几个典型的基于任务复制算法,提出了基于动态关键任务(DCT)的多处理器任务分配算法.DCT算法以克服贪心算法不足为要点,调度过程中动态计算任务时间参数,准确确定处理器的关键任务,以关键任务为核心优化调度,逐步改善调度结果,最终取得最优的调度结果.分析和实验证明,DCT算法优于现有其它同类算法.     

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     

分布式实时系统的容错调度算法

提出了两种分布式实时容错调度算法：副版本后调度算法（ＢＫＣＬ）及无容错需求后调度算法（ＮＦＲＬ）,并研究了算法的时间复杂度,这两种容雕工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,ＢＫＣＬ和ＮＦＲＬ所产生的调度可保证：在分布式系统中一个节点机失效的情况下,具有容错需求的实时任务仍然可在截止时间内完成,在描述了两个实时容错调度算法之后,分别证明了这两个算法的容错调度正确性。接着,阐述