Schedulability analysis of periodic and aperiodic tasks with resource constraints

In this paper, we address the problem of scheduling hybrid task sets consisting of hard periodic and soft aperiodic tasks that may share resources in exclusive mode in a dynamic environment, where tasks are scheduled based on their deadlines. Bounded blocking on exclusive resources is achieved by means of a dynamic resource access protocol which also prevents deadlocks and chained blocking. Aperiodic responsiveness is enhanced by an efficient servicing technique which assigns each aperiodic request a suitable deadline. Feasibility conditions are extended to handle tasks with deadlines different from periods and a reclaiming technique is presented to deal with early completions.     

混合关键级多任务调度中低关键级任务的积极处理

当前的混合关键级多任务调度,一旦高关键级任务的执行时间需求增加,通常的做法是立即抛弃相对低关键级任务,以确保高关键级任务获得足够处理器时间。考虑到数据访问的一致性和完整性以及相应的性能损失,这种处理低关键级任务的方法过于消极;同时,任务的实际执行时间并不总是能达到最差情况下执行时间,且多处理器平台上的调度存在可观的空闲时隙。因此,完全可以也应该对低关键级任务采取更为积极的处理方法。基于同构多处理器平台,构建了两类队列,一类队列容纳回收的空闲时隙,另一类队列为任务队列,包括就绪任务队列和被抛弃的低关键级任务队列,针对这两种任务队列的特性采取不同的调度方案：就绪任务队列采用混合关键级局部调度,被抛弃的低关键级任务则对空闲时隙进行分配。仿真实验表明,此调度方法在保证高关键级任务截止时限的同时,能够使混合关键级系统的可接受任务集数目获得明显提升。     

Schedulability analysis of global edf

The multiprocessor edf scheduling of sporadic task systems is studied. A new sufficient schedulability test is presented and proved correct. It is shown that this test generalizes the previously-known exact uniprocessor edf-schedulability test, and that it offers non-trivial quantitative guarantees (including a resource augmentation bound) on multiprocessors.

Schedulability analysis of dynamic priority real-time systems with contention

The Journal of Supercomputing - In multicore scheduling of hard real-time systems, there is a significant source of unpredictability due to the interference caused by the sharing of hardware...     

时间约束工作流的可调度性分析

提出一种时间约束工作流的可调度性分析方法。针对时间约束Petri网（Timing Constraint Petri Nets,TCPN）为普通Petri网无法建模多参与资源的不足,给出了扩展的时间约束Petri网（w-TCPN）的定义;结合w-TCPN的拓扑结构,从模型和实例两个层次,给出了w-TCPN变迁可调度的判定定理;提出了时间约束的调整策略。w-TCPN的研究使得时间约束工作流的建模和可调度性分析更加合理。     

优先级受限系统中可调度判定方法

在通信、雷达、导航以及各种消费类电子产品等民用和军事领域,嵌入式实时调度已逐渐成为电子电气系统的控制核心。针对同优先级任务使用FIFO调度的静态优先级系统,使用反例指出给定同优先级任务初始执行顺序的前提下,Katcher可调度判定条件的必要性不成立,提出并解析证明了FP可调度的充要条件。随机实验表明,对于高利用率下任务间执行时间差异较大的情况,约有15%的可调度任务集会被Katcher条件错判为不可调度。进一步的仿真和实例分析表明,Liu、Lehoczky、Bini等提出的条件不能判定相同优先级的情况,Katcher条件的必要性不成立,论文提到的条件能够正确判定任务集的可调度性。提出方法为实时系统调度的顶层设计提供了快速离线工具。     

On the sure criticality of tasks in activity networks withimprecise durations

The notion of the necessary criticality (both with respect to path and to activity) of a network with imprecisely defined (by means of intervals or fuzzy intervals) activity duration times is introduced and analyzed. It is shown, in the interval case, that both the problem of asserting whether a given path is necessarily critical and the problem of determining an arbitrary necessarily critical path (more exactly, a subnetwork covering all the necessarily critical paths) are easy. The corresponding solution algorithms are proposed. However, the problem of evaluating whether a given activity is necessarily critical does not seem to be so easy. Certain conditions are formulated which, in some situations (but not in all possible situations), allow the necessary criticality of activities to be evaluated. The results obtained for networks with interval activity duration times are generalized to the case of networks with fuzzy activity duration times. Two effective algorithms for calculating the degree of necessary criticality of a fixed path, as well as an algorithm for determining the paths that are necessarily critical to the maximum degree, are proposed.     

Schedulability analysis and task mapping for real-time on-chip communication

Priority-based wormhole switching with a priority share policy has been proposed as a possible solution for real-time on-chip communication. However, the blocking introduced by priority share complicates the analysis process. In this paper, we propose a new “per-priority” basis analysis scheme which computes the total time window at each priority level instead of each traffic-flow. By checking the release instance of each flow at the corresponding priority window, we can determine schedulability efficiently. Building on this static analysis, for a given set of tasks and network topology, we further propose a task mapping and priority assignment algorithm, in such a way that the hard time bounds are met with a reduced hardware overhead. Experiment results show that significant resource saving can be achieved with no performance degradation in terms of missed deadlines. By using this approach, a broad class of real-time communications with different QoS requirements can be explored and developed in a SoC/NoC communication platform.     

Schedulability analysis of fixed-priority systems using timed automata

In classic scheduling theory, real-time tasks are usually assumed to be periodic, i.e. tasks are released and computed with fixed rates periodically. To relax the stringent constraints on task arrival times, we propose to use timed automata to describe task arrival patterns. In a previous work, it is shown that the general schedulability checking problem for such models is a reachability problem for a decidable class of timed automata extended with subtraction. Unfortunately, the number of clocks needed in the analysis is proportional to the maximal number of schedulable task instances associated with a model, which is in many cases huge. In this paper, we show that for fixed-priority scheduling strategy, the schedulability checking problem can be solved using standard timed automata with two   extra clocks in addition to the clocks used in the original model to describe task arrival times. The analysis can be done in a similar manner to response time analysis in classic Rate-Monotonic Analysis (RMA). The result is further extended to systems with data-dependent control, in which the release time of a task may depend on the time-point at which other tasks finish their execution. For the case when the execution times of tasks are constants, we show that the schedulability problem can be solved using n+1$n+1$ extra clocks, where n$n$ is the number of tasks. The presented analysis techniques have been implemented in the Times tool. For systems with only periodic tasks, the performance of the tool is comparable with tools implementing the classic RMA technique based on equation-solving, without suffering from the exponential explosion in the number of tasks.     

Modeling analysis of ant system with multiple tasks and its application to spatially adjacent cell state estimate

The problem of multi-cell tracking plays an important role in studying dynamic cell cycle behaviors. In this paper, a novel ant system with multiple tasks is modeled for jointly estimating the number of cells and individual states in cell image sequences. In our ant system, in addition to pure cooperative mechanism used in traditional ant colony optimization algorithm, we model and investigate another two types of ant working modes, namely, dual competitive mode and interactive mode with cooperation and competition to evaluate the tracking performance on spatially adjacent cells. For adjacent ant colonies, dual competitive mode encourages ant colonies with different tasks to work independently, whereas the interactive mode introduces a trade-off between cooperation and competition. In simulations of real cell image sequences, the multi-tasking ant system integrated with interactive mode yielded better tracking results than systems adopting pure cooperation or dual competition alone, both of which cause tracking failures by under-estimating and over-estimating the number of cells, respectively. Furthermore, the results suggest that our algorithm can automatically and accurately track numerous cells in various scenarios, and is competitive with state-of-the-art multi-cell tracking methods.     

多处理器全局单调比率的可调度性分析

针对全局单调比率(RM)调度的多处理器系统中最高优先级任务数量少于处理器数量时,Bertogna等给出的最坏情况计算任务受到的干涉过于悲观,证明了任务受到最高优先级任务的干涉不会出现最坏情况,它受到非最高优先级任务干涉仍可能出现最坏情况。分析得出了任务受到最高优先级任务干涉的最大可能值,由此得到了一个更紧的可调度性判断条件。实验结果表明,提出的方法提高了判为可调度的任务集数量。     

Motor planning explains human behaviour in tasks with multiple solutions

How does the human central nervous system generate appropriate movements to accomplish complex motor tasks, while adapting to the changing environmental conditions? The traditional motor control research has focused on simplified tasks in which healthy human subjects were found to utilise a single solution. In this chapter we present recent works that have examined motor control and learning in richer and more natural environments. Unlike the simplified tasks, humans use multiple solutions to solve these tasks, often switching between these solutions within trials. We exhibit the requirement of an explicit planning stage in sensorimotor control models to explain these behaviours. Behavioural experiments investigating motor planning in humans are necessary to understand all the aspects of the non-conventional control and optimisation used by humans, which will also help robots to work in complex environments such as those humans live in.     

Dynamically mapping tasks with priorities and multiple deadlines in a heterogeneous environment

In a distributed heterogeneous computing system, the resources have different capabilities and tasks have different requirements. To maximize the performance of the system, it is essential to assign the resources to tasks (match) and order the execution of tasks on each resource (schedule) to exploit the heterogeneity of the resources and tasks. Dynamic mapping (defined as matching and scheduling) is performed when the arrival of tasks is not known a priori. In the heterogeneous environment considered in this study, tasks arrive randomly, tasks are independent (i.e., no inter-task communication), and tasks have priorities and multiple soft deadlines. The value of a task is calculated based on the priority of the task and the completion time of the task with respect to its deadlines. The goal of a dynamic mapping heuristic in this research is to maximize the value accrued of completed tasks in a given interval of time. This research proposes, evaluates, and compares eight dynamic mapping heuristics. Two static mapping schemes (all arrival information of tasks are known) are designed also for comparison. The performance of the best heuristics is 84% of a calculated upper bound for the scenarios considered.     

CAN总线中改进的EDF调度算法可调度性分析

针对于CAN总线的调度问题,因现有的平均分区EDF调度算法在对于优先级反转问题上收效甚微,从而导致消息缺乏一定的可调度性,故提出一种改进的基于幂函数分区的EDF算法;同时借助量化误差的概念,对该调度算法进行可调度性分析,充分论证了在该调度算法下,消息可调度的判定条件;采用CANoe平台进行实验仿真,对比平均分区EDF调度算法和双幂函数分区EDF调度算法,经试验测试验证了双幂函数分区EDF调度算法的可行性和优越性,改善了消息的最坏响应时间,提高了CAN网络通讯的实时性。     

Schedulability analysis for Controller Area Network (CAN) with FIFO queues priority queues and gateways

Controller Area Network (CAN) is widely used in automotive applications. Existing schedulability analysis for CAN is based on the assumption that the highest priority message ready for transmission at each node on the network will be entered into arbitration on the bus. However, in practice, some CAN device drivers implement FIFO rather than priority-based queues invalidating this assumption. In this paper, we introduce response time analysis and optimal priority assignment policies for CAN messages in networks where some nodes use FIFO queues while other nodes use priority queues. We show, via a case study and experimental evaluation, the detrimental impact that FIFO queues have on the real-time performance of CAN. Further, we show that in gateway applications, if it is not possible to implement a priority queue, then it is preferable to use multiple FIFO queues each allocated a small number of messages with similar transmission deadlines.     

Schedulability analysis and efficient scheduling of rate constrained messages in the TTEthernet protocol

Over time, cyber‐physical systems are becoming mixed criticality systems. As the complexity and the size of these systems grow, computation/communication resources should be more efficient than with traditional systems. TTEthernet is a communication infrastructure that enables the use of a single physical communication infrastructure for distributed mixed criticality applications while providing timely determinism. TTEthernet distinguishes between two traffic categories: the standard event triggered and the time triggered. The latter, for which higher priority is granted, is subject to strong timing guarantees because of strict periodicity constraint that fixes start‐time cycles of time‐triggered messages. In addition, event‐triggered traffic includes rate‐constrained messages that are of lower priority and have a minimum time interval between their transmission. The paper proposes both an on‐line efficient scheduling algorithm and a necessary and sufficient schedulability condition based on the worst case response time computation for rate‐constrained messages while taking into account time‐triggered messages transmission. Copyright © 2017 John Wiley & Sons, Ltd.     

Novel approaches to control multiple tasks in redundant manipulators: stability analysis and performance evaluation

In this paper, two new approaches for handling multiple tasks in redundant manipulators based on predefined allocated priorities are proposed. The first approach is an integrated scheme which employs null-space base vector for handling prioritized tasks. Clear task and null-space representation, better execution of the lower priority tasks, and intuitive formulation are its basic features. The second approach aims to improve the performance of all the prioritized tasks, especially during algorithmic singularities beside clear null-space dynamics representation. This approach can be considered as a modification and extension of the Reverse Priority (RP) algorithm in acceleration level. The commands related to each tasks are added to each other following reverse order of priorities and by suitable projectors. The projector definition is given using minimal representation of the null-space. Clear null-space dynamics in the proposed methods facilitate the stability analysis. A detailed evaluation by means of computer simulation in various cases is reported. Tasks accomplishment using the proposed approaches is compared with the classic method. The results, in general, show higher performance and accuracy of the tasks by the proposed approaches.     

实时事务调度及静态可调度性分析

在类似闭环控制的硬实时数据库应用环境,实时事务具有一定的静态可预报性,其中实时事务的可调度性分析是维护实时数据库时间正确性的基础.通过利用抢占阈值,提出了一种新的实时事务处理模型,它集成了CPU调度和数据调度,实现离线并发控制,具有单阻塞的特征与好的静态可预测性,并有利于降低事务系统的负载和改善可调度性.进一步由此建立了实时事务的静态可调度性分析模型以及求最优可行调度的整数规划模型,该模型有利于达到实时事务调度的整体优化.