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A Generic Coq Proof of Typical Worst-Case Analysis 典型最坏情况分析的一般Coq证明
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00039
Pascal Fradet, Maxime Lesourd, J. Monin, Sophie Quinton
This paper presents a generic proof of Typical Worst-Case Analysis (TWCA), an analysis technique for weakly-hard real-time uniprocessor systems. TWCA was originally introduced for systems with fixed priority preemptive (FPP) schedulers and has since been extended to fixed-priority nonpreemptive (FPNP) and earliest-deadline-first (EDF) schedulers. Our generic analysis is based on an abstract model that characterizes the exact properties needed to make TWCA applicable to any system model. Our results are formalized and checked using the Coq proof assistant along with the Prosa schedulability analysis library. Our experience with formalizing real-time systems analyses shows that this is not only a way to increase confidence in our claimed results: The discipline required to obtain machine checked proofs helps understanding the exact assumptions required by a given analysis, its key intermediate steps and how this analysis can be generalized.
本文给出了典型最坏情况分析(TWCA)的一般证明,TWCA是一种用于弱硬实时单处理器系统的分析技术。TWCA最初是为具有固定优先级抢占(FPP)调度程序的系统引入的,后来扩展到固定优先级非抢占(FPNP)和最早截止日期优先(EDF)调度程序。我们的一般分析基于一个抽象模型,该模型描述了使TWCA适用于任何系统模型所需的确切属性。使用Coq证明助手以及Prosa可调度性分析库对我们的结果进行形式化和检查。我们在形式化实时系统分析方面的经验表明,这不仅是增加我们声称的结果的信心的一种方法:获得机器检查证明所需的规程有助于理解给定分析所需的确切假设,其关键中间步骤以及该分析如何推广。
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引用次数: 6
Work-in-Progress: Extending Buffer-Aware Worst-Case Timing Analysis of Wormhole NoCs 正在进行的工作:扩展缓冲区感知虫洞noc的最坏情况时序分析
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00032
Frederic Giroudot, A. Mifdaoui
Worst-case timing analysis of Networks-on-Chip (NoCs) is a crucial aspect to design safe real-time systems based on manycore architectures. In this paper, we present some potential extensions of our previously-published buffer-aware worst-case timing analysis approach to cope with bursty traffic such as real-time audio and video streams. A first promising lead is to improve the algorithm analyzing backpressure patterns to capture consecutive-packet queueing effect while keeping the information about the dependencies between flows. Furthermore, the improved algorithm may also decrease the inherent complexity of computing the indirect blocking latency due to backpressure.
片上网络(noc)的最坏时序分析是设计基于多核架构的安全实时系统的一个重要方面。在本文中,我们提出了我们之前发布的缓冲区感知最坏时间分析方法的一些潜在扩展,以应对突发流量,如实时音频和视频流。第一个有希望的进展是改进分析背压模式的算法,以捕获连续数据包排队效果,同时保留有关流之间依赖关系的信息。此外,改进算法还可以降低计算背压间接阻塞延迟的固有复杂度。
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引用次数: 1
NoCo: ILP-Based Worst-Case Contention Estimation for Mesh Real-Time Manycores 基于ilp的网格实时多核最坏情况争用估计
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00043
Jordi Cardona, Carles Hernández, E. Mezzetti, J. Abella, F. Cazorla
Manycores are capable of providing the computational demands required by functionally-advanced critical applications in domains such as automotive and avionics. In manycores a network-on-chip (NoC) provides access to shared caches and memories and hence concentrates most of the contention that tasks suffer, with effects on the worst-case contention delay (WCD) of packets and tasks' WCET. While several proposals minimize the impact of individual NoC parameters on WCD, e.g. mapping and routing, there are strong dependences among these NoC parameters. Hence, finding the optimal NoC configurations requires optimizing all parameters simultaneously, which represents a multidimensional optimization problem. In this paper we propose NoCo, a novel approach that combines ILP and stochastic optimization to find NoC configurations in terms of packet routing, application mapping, and arbitration weight allocation. Our results show that NoCo improves other techniques that optimize a subset of NoC parameters.
多核能够提供汽车和航空电子等领域功能先进的关键应用所需的计算需求。在多核中,片上网络(NoC)提供了对共享缓存和内存的访问,因此集中了任务所遭受的大部分争用,对数据包的最坏情况争用延迟(WCD)和任务的WCET有影响。虽然有几个建议尽量减少单个NoC参数对WCD的影响,例如映射和路由,但这些NoC参数之间存在很强的依赖性。因此,寻找最佳NoC配置需要同时优化所有参数,这是一个多维优化问题。在本文中,我们提出了NoCo,这是一种结合了ILP和随机优化的新方法,可以在分组路由,应用映射和仲裁权重分配方面找到NoC配置。我们的研究结果表明,NoCo改进了其他优化NoC参数子集的技术。
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引用次数: 8
Uniprocessor Mixed-Criticality Scheduling with Graceful Degradation by Completion Rate 基于完成率优雅退化的单处理器混合临界调度
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00052
Zhishan Guo, Kecheng Yang, Sudharsan Vaidhun, Samsil Arefin, Sajal K. Das, Haoyi Xiong
The scheduling of mixed-criticality (MC) systems with graceful degradation is considered, where LO-criticality tasks are guaranteed some service in HI mode in the form of minimum cumulative completion rates. First, we present an easy to implement admission-control procedure to determine which LO-criticality jobs to complete in HI mode. Then, we propose a demand-bound-function-based MC schedulability test that runs in pseudo-polynomial time for such systems under EDF-VD scheduling, wherein two virtual deadline setting heuristics are considered. Furthermore, we discuss a mechanism for the system to switch back from HI to LO mode and quantify the maximum time duration such recovery process would take. Finally, we show the effectiveness of our proposed method by experimental evaluation in comparison to state-of-the-art MC schedulers.
考虑具有优雅退化的混合临界(MC)系统的调度问题,其中低临界任务以最小累积完成率的形式在HI模式下保证某些服务。首先,我们提出了一个易于实现的准入控制程序,以确定在HI模式下完成哪些低临界作业。然后,我们提出了一个基于需求约束函数的MC可调度性测试,该测试在EDF-VD调度下在伪多项式时间内运行,其中考虑了两个虚拟截止日期设置启发式。此外,我们还讨论了系统从HI模式切换回LO模式的机制,并量化了这种恢复过程所需的最大持续时间。最后,我们通过实验评估与最先进的MC调度程序进行了比较,证明了我们提出的方法的有效性。
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引用次数: 26
Semi-Extended Tasks: Efficient Stack Sharing Among Blocking Threads 半扩展任务:阻塞线程之间的有效堆栈共享
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00049
Christian J. Dietrich, D. Lohmann
Memory is an expensive and, therefore, limited resource in deeply embedded real-time systems. Thread stacks substantially contribute to the RAM requirements. To reduce the system's worst-case stack consumption (WCSC), it is state of the art to exploit thread-level preemption constraints to let multiple threads share the same stack. However, deriving a tight, yet correct bound for the shared stack is a difficult undertaking and stack sharing is currently restricted to run-to-completion threads, which are preemptable, but cannot block (i.e., passively wait for an event) at run time. With semi-extended tasks (SETs), we propose a solution for efficient stack sharing among blocking and non-blocking threads on the system level. For this, we refine the stack-sharing granularity from the thread to function level. We provide an efficient intra-thread stack-switch mechanism and an ILP-based WCSC analysis that considers fine-grained preemption constraints and possible function-level switching points from the private to the shared stack. A genetic algorithm then selects switching points that lead to the reduction of the overall WCSC. Compared to systems that run only non-blocking threads on the shared stack, semi-extended tasks decrease the WCSC in our benchmarks on average by 7 percent and up to 52 percent for some systems.
在深度嵌入式实时系统中,内存是一种昂贵且有限的资源。线程栈很大程度上增加了RAM需求。为了减少系统最坏情况下的堆栈消耗(WCSC),利用线程级抢占约束让多个线程共享同一个堆栈是目前最先进的技术。然而,为共享堆栈派生一个紧凑而正确的边界是一项困难的任务,堆栈共享目前仅限于运行到完成的线程,这些线程是可抢占的,但不能在运行时阻塞(即被动等待事件)。利用半扩展任务(set),我们提出了一种在系统级阻塞和非阻塞线程之间有效共享堆栈的解决方案。为此,我们细化了从线程到函数级别的堆栈共享粒度。我们提供了一种有效的线程内堆栈切换机制和基于ilp的WCSC分析,该分析考虑了细粒度抢占约束和从私有堆栈到共享堆栈的可能的功能级切换点。然后,遗传算法选择切换点,从而降低总体WCSC。与在共享堆栈上只运行非阻塞线程的系统相比,半扩展任务在我们的基准测试中平均降低了7%的WCSC,在某些系统中最高可降低52%。
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引用次数: 1
Real-Time Computing and the Evolution of Embedded System Designs 实时计算与嵌入式系统设计的演变
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00011
Tei-Wei Kuo, Jian-Jia Chen, Yuan-Hao Chang, P. Hsiu
Real-time computing provides insightful ways to explore the optimization in resource usages, especially from the time point of view. Nevertheless, real-time task scheduling is recognized by its high complexity when there are non-preemptive shared resources and multiple processors. When more and more practical factors in system designs are considered, such as energy consumption and memory allocation, even some sub-problems in real-time task scheduling become intractable. Although people often criticize various artificial assumptions in real-time task scheduling, they have to admit that ideas in real-time computing and their extensions, such as tradeoff in cost, performance, energy, and even the quality of service, can be applied to multi-dimensional optimization in system designs. In this direction, we witness the rapid development of the embedded system industry and join the task force in system designs, especially mobile devices and non-volatile memory systems. Resource management on mobile devices, with a special emphasis on user experience, should not only consider the response time but also the visual perception of users. Non-volatile memory has also blurred the boundary between the memory and the storage. It enables certain unified considerations of the main memory and storage and also in-memory computing. It shows the ways to break the boundaries between hardware and software layers and have better integration of computing and memory/storage units. The advances in mobile systems and memory innovations inspire the evolution of embedded system designs and have also brought us insights to solutions regarding how systems should be restructured and how computing should be done. They might also provide their feedback to real-time computing and even shape the future direction of real-time computing in various innovative ways.
实时计算提供了深入的方法来探索资源使用的优化,特别是从时间的角度来看。然而,当存在非抢占式共享资源和多处理器时,实时任务调度的复杂性较高。当系统设计中考虑到越来越多的实际因素,如能耗和内存分配时,实时任务调度中的一些子问题也变得棘手起来。尽管人们经常批评实时任务调度中的各种人为假设,但他们不得不承认,实时计算中的思想及其扩展,如成本、性能、能源甚至服务质量的权衡,都可以应用于系统设计中的多维优化。在这个方向上,我们见证了嵌入式系统行业的快速发展,并加入了系统设计的工作组,特别是移动设备和非易失性存储系统。移动设备上的资源管理,特别强调用户体验,不仅要考虑响应时间,还要考虑用户的视觉感受。非易失性存储器也模糊了存储器和存储器之间的界限。它可以统一考虑主内存和存储以及内存中的计算。它展示了打破硬件和软件层之间界限的方法,以及更好地集成计算和内存/存储单元的方法。移动系统和内存创新的进步激发了嵌入式系统设计的演变,也给我们带来了关于系统应该如何重组和计算应该如何完成的解决方案的见解。他们还可能为实时计算提供反馈,甚至以各种创新的方式塑造实时计算的未来方向。
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引用次数: 5
Work-in-Progress: Precise Scheduling of Mixed-Criticality Tasks by Varying Processor Speed 在制品:不同处理器速度下混合临界任务的精确调度
Pub Date : 2018-12-01 DOI: 10.1145/3356401.3356410
S. Sruti, Ashikahmed Bhuiyan, Zhishan Guo
The traditional mixed-criticality (MC) model does not allow less critical tasks to execute during an event of the error and exception. Recently, the imprecise MC (IMC) model has been proposed where, even for exceptional events, less critical tasks also receive some amount of (degraded) service, e.g., a task overruns its execution demand. In this work, we present our ongoing effort to extend the IMC model to the precise scheduling of tasks and integrate with the dynamic voltage and frequency scaling (DVFS) scheme to enable energy minimization. Precise scheduling of MC systems is highly challenging because of its requirement to simultaneously guarantee the timing correctness of all tasks under both pessimistic and less pessimistic assumptions. We propose an utilization-based schedulability test and sufficient schedulability conditions for such systems under earliest deadline first with virtual deadline (EDF-VD) scheduling policy. For this unified model, we present a quantitative study in the forms of speedup bound and approximation ratio. Finally, both theoretical and experimental analysis will be conducted to prove the correctness of our algorithm and to demonstrate its effectiveness.
传统的混合临界(MC)模型不允许在错误和异常事件期间执行不那么关键的任务。最近,提出了不精确MC (IMC)模型,其中即使对于异常事件,不太关键的任务也会收到一定数量的(降级的)服务,例如,任务超出其执行需求。在这项工作中,我们展示了我们正在进行的努力,将IMC模型扩展到任务的精确调度,并与动态电压和频率缩放(DVFS)方案集成,以实现能量最小化。MC系统的精确调度具有很高的挑战性,因为它要求同时保证所有任务在悲观和非悲观假设下的时间正确性。提出了一种基于利用率的可调度性测试方法,并给出了采用虚拟截止日期(EDF-VD)调度策略的系统可调度性的充分条件。对于这个统一模型,我们给出了加速界和近似比形式的定量研究。最后,通过理论分析和实验分析来证明算法的正确性和有效性。
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引用次数: 29
Work-in-Progress: Making Machine Learning Real-Time Predictable 正在进行的工作:使机器学习实时可预测
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00029
Hang Xu, F. Mueller
Machine learning (ML) on edge computing devices is becoming popular in the industry as a means to make control systems more intelligent and autonomous. The new trend is to utilize embedded edge devices, as they boast higher computational power and larger memories than before, to perform ML tasks that had previously been limited to cloud-hosted deployments. In this work, we assess the real-time predictability and consider data privacy concerns by comparing traditional cloud services with edge-based ones for certain data analytics tasks. We identify the subset of ML problems appropriate for edge devices by investigating if they result in real-time predictable services for a set of widely used ML libraries. We specifically enhance the Caffe library to make it more suitable for real-time predictability. We then deploy ML models with high accuracy scores on an embedded system, exposing it to industry sensor data from the field, to demonstrates its efficacy and suitability for real-time processing.
边缘计算设备上的机器学习(ML)作为使控制系统更加智能和自主的一种手段,在行业中越来越流行。新的趋势是利用嵌入式边缘设备,因为它们拥有比以前更高的计算能力和更大的内存,来执行以前仅限于云托管部署的机器学习任务。在这项工作中,我们通过比较传统云服务和基于边缘的云服务来评估实时可预测性,并考虑数据隐私问题,以完成某些数据分析任务。我们通过调查机器学习问题是否会为一组广泛使用的机器学习库提供实时可预测的服务,来确定适合边缘设备的机器学习问题子集。我们特别增强了Caffe库,使其更适合实时可预测性。然后,我们在嵌入式系统上部署具有高精度分数的机器学习模型,将其暴露于来自现场的工业传感器数据,以证明其对实时处理的有效性和适用性。
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引用次数: 4
Outstanding Paper Awards 优秀论文奖
Pub Date : 2018-12-01 DOI: 10.1109/rtss.2018.00006
J. Erickson, James H. Anderson, Gurulingesh Raravi, B. Andersson, K. Bletsas, Vincent Nélis, Sanjoy Baruah
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引用次数: 0
Exploiting Locality for the Performance Analysis of Shared Memory Systems in MPSoCs 利用局部性分析mpsoc中共享内存系统的性能
Pub Date : 2018-12-01 DOI: 10.1109/RTSS.2018.00050
Selma Saidi, A. Syring
The integration trend and increased required computing power is driving the advent of common embedded consumer devices like MPSoCs platforms in the safety critical domain. MPSoCs often feature a shared tightly-coupled memory system where a careful management of data storage and transfers is a key enabler for performance. However, providing real-time guarantees for these platforms is extremely challenging as they rely on exploiting data locality to improve average latencies in shared-memory architectures. This effect is often disregarded by existing real-time analysis approaches which furthermore often focus solely on a single component of the memory system. In this paper, we propose a framework for the timing analysis of shared memory systems composed of on-chip scratchpad memories, off-chip DRAMs and DMA engines. The analysis captures the effect on the performance of the system of the locality of accesses, their interleaving and granularity.
集成趋势和对计算能力需求的增加推动了安全关键领域常见嵌入式消费设备(如mpsoc平台)的出现。mpsoc通常具有共享的紧密耦合内存系统,其中仔细管理数据存储和传输是提高性能的关键因素。然而,为这些平台提供实时保证是极具挑战性的,因为它们依赖于利用数据局部性来改善共享内存架构中的平均延迟。这种影响经常被现有的实时分析方法所忽视,这些方法往往只关注记忆系统的单个组件。在本文中,我们提出了一个由片上刮板存储器、片外dram和DMA引擎组成的共享存储器系统的时序分析框架。该分析捕获了访问的局部性、它们的交错和粒度对系统性能的影响。
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引用次数: 6
期刊
2018 IEEE Real-Time Systems Symposium (RTSS)
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