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Deterministic Memory Abstraction and Supporting Multicore System Architecture 确定性内存抽象和支持多核系统架构
Pub Date : 2017-07-17 DOI: 10.4230/LIPIcs.ECRTS.2018.1
F. Farshchi, P. K. Valsan, R. Mancuso, H. Yun
Poor time predictability of multicore processors has been a long-standing challenge in the real-time systems community. In this paper, we make a case that a fundamental problem that prevents efficient and predictable real-time computing on multicore is the lack of a proper memory abstraction to express memory criticality, which cuts across various layers of the system: the application, OS, and hardware. We, therefore, propose a new holistic resource management approach driven by a new memory abstraction, which we call Deterministic Memory. The key characteristic of deterministic memory is that the platform - the OS and hardware - guarantees small and tightly bounded worst-case memory access timing. In contrast, we call the conventional memory abstraction as best-effort memory in which only highly pessimistic worst-case bounds can be achieved. We propose to utilize both abstractions to achieve high time predictability but without significantly sacrificing performance. We present deterministic memory-aware OS and architecture designs, including OS-level page allocator, hardware-level cache, and DRAM controller designs. We implement the proposed OS and architecture extensions on Linux and gem5 simulator. Our evaluation results, using a set of synthetic and real-world benchmarks, demonstrate the feasibility and effectiveness of our approach.
多核处理器时间可预测性差一直是实时系统界面临的一个长期挑战。在本文中,我们提出了一个案例,即阻碍多核上高效和可预测的实时计算的一个基本问题是缺乏适当的内存抽象来表达内存临界性,这跨越了系统的各个层:应用程序、操作系统和硬件。因此,我们提出了一种新的整体资源管理方法,该方法由一种新的内存抽象驱动,我们称之为确定性内存。确定性内存的关键特征是平台(操作系统和硬件)保证较小且严格限定的最坏情况内存访问时间。相反,我们把传统的记忆抽象称为“最佳努力记忆”,它只能达到高度悲观的最坏情况界限。我们建议利用这两种抽象来实现高时间可预测性,但不会显著牺牲性能。我们提出了确定性的内存感知操作系统和体系结构设计,包括操作系统级页面分配器、硬件级缓存和DRAM控制器设计。我们在Linux和gem5模拟器上实现了所提出的操作系统和体系结构扩展。我们的评估结果,使用一组合成和现实世界的基准,证明了我们的方法的可行性和有效性。
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引用次数: 20
Cache-Conscious Offline Real-Time Task Scheduling for Multi-Core Processors 基于缓存意识的多核处理器离线实时任务调度
Pub Date : 2017-06-27 DOI: 10.4230/LIPIcs.ECRTS.2017.14
V. Nguyen, D. Hardy, I. Puaut
Most schedulability analysis techniques for multi-core architectures assume a single Worst-Case Execution Time (WCET) per task, which is valid in all execution conditions. This assumption is too pessimistic for parallel applications running on multi-core architectures with local instruction or data caches, for which the WCET of a task depends on the cache contents at the beginning of its execution, itself depending on the task that was executed before the task under study. In this paper, we propose two scheduling techniques for multi-core architectures equipped with local instruction and data caches. The two techniques schedule a parallel application modeled as a task graph, and generate a static partitioned non-preemptive schedule. We propose an optimal method, using an Integer Linear Programming (ILP) formulation, as well as a heuristic method based on list scheduling. Experimental results show that by taking into account the effect of private caches on tasks' WCETs, the length of generated schedules is significantly reduced as compared to schedules generated by cache-unaware scheduling methods. The observed schedule length reduction on streaming applications is 11% on average for the optimal method and 9% on average for the heuristic method.
大多数多核体系结构的可调度性分析技术假设每个任务有一个最坏情况执行时间(WCET),它在所有执行条件下都有效。这个假设对于运行在多核架构上的并行应用程序来说太悲观了,因为这些并行应用程序具有本地指令或数据缓存,任务的WCET取决于其执行开始时的缓存内容,而其本身取决于在研究任务之前执行的任务。本文提出了两种具有本地指令和数据缓存的多核架构调度技术。这两种技术调度建模为任务图的并行应用程序,并生成静态分区的非抢占调度。我们提出了一种最优方法,使用整数线性规划(ILP)公式,以及一种基于列表调度的启发式方法。实验结果表明,与不考虑缓存的调度方法相比,考虑了私有缓存对任务wcet的影响,生成的调度长度显著缩短。观察到,流应用程序的调度长度平均减少了最优方法的11%,启发式方法的平均减少了9%。
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引用次数: 14
Budgeting Under-Specified Tasks for Weakly-Hard Real-Time Systems 对弱硬实时系统的未指定任务进行预算
Pub Date : 2017-06-27 DOI: 10.4230/LIPIcs.ECRTS.2017.17
Zain Alabedin Haj Hammadeh, Sophie Quinton, Marco Panunzio, R. Henia, L. Rioux, R. Ernst
In this paper, we present an extension of slack analysis for budgeting in the design of weakly-hard real-time systems. During design, it often happens that some parts of a task set are fully specified while other parameters, e.g. regarding recovery or monitoring tasks, will be available only much later. In such cases, slack analysis can help anticipate how these missing parameters can influence the behavior of the whole system so that a resource budget can be allocated to them. It is, however, sufficient in many application contexts to budget these tasks in order to preserve weakly-hard rather than hard guarantees. We thus present an extension of slack analysis for deriving task budgets for systems with hard and weakly-hard requirements. This work is motivated by and validated on a realistic case study inspired by industrial practice. 1998 ACM Subject Classification B.8.2 Performance Analysis and Design Aids
在本文中,我们提出了在弱硬实时系统设计中预算松弛分析的一个扩展。在设计过程中,经常会发生这样的情况:任务集的某些部分是完全指定的,而其他参数,例如关于恢复或监控任务的参数,要等到很久以后才可用。在这种情况下,松弛分析可以帮助预测这些缺失的参数如何影响整个系统的行为,从而可以将资源预算分配给它们。然而,在许多应用程序上下文中,预算这些任务就足够了,以便保留弱硬保证而不是硬保证。因此,我们提出了松弛分析的扩展,用于为具有硬需求和弱硬需求的系统导出任务预算。这项工作是由工业实践启发的现实案例研究所激发和验证的。1998 ACM主题分类B.8.2性能分析和设计辅助工具
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引用次数: 16
A Linux Real-Time Packet Scheduler for Reliable Static SDN Routing 用于可靠静态SDN路由的Linux实时包调度程序
Pub Date : 2017-06-01 DOI: 10.4230/LIPIcs.ECRTS.2017.25
Tao Qian, F. Mueller, Yufeng Xin
In a distributed computing environment, guaranteeing the hard deadline for real-time messages is essential to ensure schedulability of real-time tasks. Since capabilities of the shared resources for transmission are limited, e.g., the buffer size is limited on network devices, it becomes a challenge to design an effective and feasible resource sharing policy based on both the demand of real-time packet transmissions and the limitation of resource capabilities. We address this challenge in two cooperative mechanisms. First, we design a static routing algorithm to find forwarding paths for packets to guarantee their hard deadlines. The routing algorithm employs a validation-based backtracking procedure capable of deriving the demand of a set of real-time packets on each shared network device, and it checks whether this demand can be met on the device. Second, we design a packet scheduler that runs on network devices to transmit messages according to our routing requirements. We implement these mechanisms on virtual software-defined network (SDN) switches and evaluate them on real hardware in a local cluster to demonstrate the feasibility and effectiveness of our routing algorithm and packet scheduler.
在分布式计算环境中,保证实时消息的硬截止日期对于确保实时任务的可调度性至关重要。由于共享资源的传输能力是有限的,例如网络设备上的缓冲区大小是有限的,因此如何在满足数据包实时传输需求的同时,考虑到资源能力的限制,设计一种有效可行的资源共享策略成为一个挑战。我们通过两个合作机制应对这一挑战。首先,我们设计了一个静态路由算法来寻找数据包的转发路径,以保证它们的硬截止日期。路由算法采用基于验证的回溯过程,能够在每个共享网络设备上推导出一组实时数据包的需求,并检查该设备是否可以满足该需求。其次,我们设计了一个在网络设备上运行的数据包调度程序,根据我们的路由要求来传输消息。我们在虚拟软件定义网络(SDN)交换机上实现了这些机制,并在本地集群的实际硬件上对它们进行了评估,以证明我们的路由算法和数据包调度程序的可行性和有效性。
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引用次数: 10
Applying Real-Time Scheduling Theory to the Synchronous Data Flow Model of Computation 实时调度理论在计算同步数据流模型中的应用
Pub Date : 2017-06-01 DOI: 10.4230/LIPIcs.ECRTS.2017.8
Abhishek Singh, Pontus Ekberg, Sanjoy Baruah
Schedulability analysis techniques that are well understood within the real-time scheduling community are applied to the analysis of recurrent real-time workloads that are modeled using the synchronous data-flow graph (SDFG) model. An enhancement to the standard SDFG model is proposed, that permits the specification of a real-time latency constraint between a specified input and a specified output of an SDFG. A technique is derived for transforming such an enhanced SDFG to a collection of traditional 3-parameter sporadic tasks, thereby allowing for the analysis of systems of SDFG tasks using the methods and algorithms that have previously been developed within the real-time scheduling community for the analysis of systems of such sporadic tasks. The applicability of this approach is illustrated by applying prior results from real-time scheduling theory to construct an exact preemptive uniprocessor schedulability test for collections of recurrent processes that are each represented using the enhanced SDFG model.
可调度性分析技术在实时调度社区中得到了很好的理解,它被应用于分析使用同步数据流图(SDFG)模型建模的反复出现的实时工作负载。提出了对标准SDFG模型的改进,允许在SDFG的指定输入和指定输出之间指定实时延迟约束。一种将这种增强的SDFG转换为传统的3参数零星任务集合的技术被衍生出来,从而允许使用之前在实时调度社区中开发的用于分析此类零星任务系统的方法和算法来分析SDFG任务系统。通过应用实时调度理论的先验结果来构建一个精确的抢占式单处理器可调度性测试,说明了该方法的适用性,该测试用于使用增强的SDFG模型表示的循环进程集合。
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引用次数: 6
WCET Derivation under Single Core Equivalence with Explicit Memory Budget Assignment 具有显式内存预算分配的单核等价的WCET派生
Pub Date : 2017-06-01 DOI: 10.4230/LIPIcs.ECRTS.2017.3
R. Mancuso, R. Pellizzoni, Neriman Tokcan, M. Caccamo
In the last decade there has been a steady uptrend in the popularity of embedded multi-core platforms. This represents a turning point in the theory and implementation of real-time systems. From a real-time standpoint, however, the extensive sharing of hardware resources (e.g. caches, DRAM subsystem, I/O channels) represents a major source of unpredictability. Budget-based memory regulation (throttling) has been extensively studied to enforce a strict partitioning of the DRAM subsystem’s bandwidth. The common approach to analyze a task under memory bandwidth regulation is to consider the budget of the core where the task is executing, and assume the worst-case about the remaining cores' budgets. In this work, we propose a novel analysis strategy to derive the WCET of a task under memory bandwidth regulation that takes into account the exact distribution of memory budgets to cores. In this sense, the proposed analysis represents a generalization of approaches that consider (i) even budget distribution across cores; and (ii) uneven but unknown (except for the core under analysis) budget assignment. By exploiting the additional piece of information, we show that it is possible to derive a more accurate WCET estimation. Our evaluations highlight that the proposed technique can reduce overestimation by 30% in average, and up to 60%, compared to the state of the art.
在过去的十年中,嵌入式多核平台的流行呈稳步上升趋势。这是实时系统理论和实现的一个转折点。然而,从实时的角度来看,硬件资源的广泛共享(例如缓存、DRAM子系统、I/O通道)是不可预测性的主要来源。基于预算的内存调节(节流)已经被广泛研究,以强制严格划分DRAM子系统的带宽。在内存带宽调节下分析任务的常用方法是考虑执行任务所在核心的预算,并假设剩余核心预算的最坏情况。在这项工作中,我们提出了一种新的分析策略来推导内存带宽调节下任务的WCET,该策略考虑了内存预算到内核的确切分布。从这个意义上说,拟议的分析是考虑到(i)各核心之间预算分配均匀的方法的概括;(二)预算分配不均但未知(分析核心除外)。通过利用额外的信息片段,我们表明可以推导出更准确的WCET估计。我们的评估强调,与目前的技术水平相比,所提出的技术可以平均减少30%的高估,最多可减少60%。
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引用次数: 25
Optimal Dataflow Scheduling on a Heterogeneous Multiprocessor With Reduced Response Time Bounds 异构多处理器响应时间限制下的最优数据流调度
Pub Date : 2017-06-01 DOI: 10.4230/LIPIcs.ECRTS.2017.15
Zheng Dong, Cong Liu, A. Gatherer, L. McFearin, P. Yan, James H. Anderson
Heterogeneous computing platforms with multiple types of computing resources have been widely used in many industrial systems to process dataflow tasks with pre-defined affinity of tasks to subgroups of resources. For many dataflow workloads with soft real-time requirements, guaranteeing fast and bounded response times is often the objective. This paper presents a new set of analysis techniques showing that a classical real-time scheduler, namely earliest-deadline first (EDF), is able to support dataflow tasks scheduled on such heterogeneous platforms with provably bounded response times while incurring no resource capacity loss, thus proving EDF to be an optimal solution for this scheduling problem. Experiments using synthetic workloads with widely varied parameters also demonstrate that the magnitude of the response time bounds yielded under the proposed analysis is reasonably small under all scenarios. Compared to the state-of-the-art soft real-time analysis techniques, our test yields a 68% reduction on response time bounds on average. This work demonstrates the potential of applying EDF into practical industrial systems containing dataflow-based workloads that desire guaranteed bounded response times.
具有多种类型计算资源的异构计算平台已广泛应用于许多工业系统中,用于处理具有预定义的任务与资源子组关联的数据流任务。对于许多具有软实时需求的数据流工作负载,保证快速和有限的响应时间通常是目标。本文提出了一组新的分析技术,表明经典的实时调度程序,即最早截止日期优先(EDF),能够支持在这种异构平台上调度的数据流任务,并且具有可证明的有限响应时间,同时不会产生资源容量损失,从而证明EDF是该调度问题的最优解决方案。使用具有广泛不同参数的合成工作负载的实验也表明,在所有场景下,根据所提出的分析产生的响应时间界限的幅度都相当小。与最先进的软实时分析技术相比,我们的测试平均减少了68%的响应时间界限。这项工作展示了将EDF应用于实际工业系统的潜力,这些系统包含基于数据流的工作负载,需要保证有限的响应时间。
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引用次数: 10
Improving the Quality-of-Service for Scheduling Mixed-Criticality Systems on Multiprocessors 改进多处理器混合临界系统调度的服务质量
Pub Date : 2017-05-31 DOI: 10.4230/LIPIcs.ECRTS.2017.19
R. Pathan
The traditional Vestal's model of Mixed-Criticality (MC) systems was recently extended to Imprecise Mixed-Critical task model (IMC) to guarantee some minimum level of (degraded) service to the low-critical tasks even after the system switches to the high-critical behavior. This paper extends the IMC task model by associating specific Quality-of-Service (QoS) values with the low-critical tasks and proposes a fluid-based scheduling algorithm, called MCFQ, for such task model. The MCFQ algorithm allows some low-critical tasks to provide full service even during the high-critical behavior so that the QoS of the overall system is increased. To the best of our knowledge MCFQ is the first algorithm for IMC task sets considering multiprocessor platform and QoS values. By extending the recently proposed MC-Fluid and MCF fluid-based multiprocessor scheduling algorithms for IMC task model, empirical results show that MCFQ algorithm can significantly improve the QoS of the system in comparison to that of both MC-Fluid and MCF. In addition, the schedulability performance of MCFQ is very close to the optimal MC-Fluid algorithm. Finally, we prove that the MCFQ algorithm has a speedup bound of 4/3, which is optimal for IMC tasks.
传统的混合临界系统的Vestal模型最近被扩展到不精确混合临界任务模型(IMC),以保证即使系统切换到高临界行为后,对低临界任务的最低(降级)服务水平。本文通过将特定的服务质量(QoS)值与低关键任务相关联,扩展了IMC任务模型,并针对该任务模型提出了一种基于流体的调度算法MCFQ。MCFQ算法允许一些低关键任务在高关键行为期间提供完整的服务,从而提高整个系统的QoS。据我们所知,MCFQ是第一个考虑多处理器平台和QoS值的IMC任务集算法。通过将最近提出的MC-Fluid和MCF基于流体的多处理器调度算法扩展到IMC任务模型,实证结果表明,与MC-Fluid和MCF算法相比,MCFQ算法可以显著提高系统的QoS。此外,MCFQ的可调度性能非常接近最优MC-Fluid算法。最后,我们证明了MCFQ算法的加速界为4/3,对于IMC任务是最优的。
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引用次数: 18
Replica-Aware Co-Scheduling for Mixed-Criticality 基于副本感知的混合临界协同调度
Pub Date : 2017-05-31 DOI: 10.4230/LIPIcs.ECRTS.2017.20
Eberle A. Rambo, R. Ernst
Cross-layer fault-tolerance solutions are the key to effectively and efficiently increase the reliability in future safety-critical real-time systems. Replicated software execution with hardware support for error detection is a cross-layer approach that exploits future many-core platforms to increase reliability without resorting to redundancy in hardware. The performance of such systems, however, strongly depends on the scheduler. Standard schedulers, such as Partitioned Strict Priority Preemptive (SPP) and Time-Division Multiplexing (TDM)-based ones, although widely employed, provide poor performance in face of replicated execution. In this paper, we propose the replica-aware co-scheduling for mixed-critical systems. Experimental results show schedulability improvements of more than 1.5x when compared to TDM and 6.9x when compared to SPP. 1998 ACM Subject Classification C.4 Performance of Systems
跨层容错解决方案是提高未来安全关键型实时系统可靠性的关键。使用硬件支持错误检测的复制软件执行是一种跨层方法,它利用未来的多核心平台来提高可靠性,而无需借助硬件冗余。然而,这类系统的性能很大程度上依赖于调度器。标准调度器,如分区严格优先级抢占(SPP)和基于时分多路复用(TDM)的调度器,虽然被广泛使用,但在面对复制执行时性能很差。本文提出了混合关键系统的副本感知协同调度方法。实验结果表明,与TDM相比,可调度性提高了1.5倍以上,与SPP相比提高了6.9倍。1998 ACM主题分类C.4系统性能
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引用次数: 10
QoS, Consumer Electronics, and Real-Time: Challenges and Opportunities QoS、消费电子和实时:挑战与机遇
Pub Date : 2002-06-19 DOI: 10.1109/ECRTS.2002.10005
Elisabeth F. M. Steffens
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引用次数: 1
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Euromicro Conference on Real-Time Systems
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