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Annual International Symposium on Computer Architecture, ISCA

作者： J. Hall K.G. Shin J. Rexford Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Dearborn Ann Arbor MI USA

Parallel machines have the potential to satisfy the large computational demands of emerging real-time applications. These applications require a predictable communication network, where time-constrained traffic requires bounds on latency or throughput while good average performance suffices for best-effort packets. This paper presents a router architecture that tailors low-level routing, switching, arbitration and flow-control policies to the conflicting demands of each traffic class. The router implements deadline-based scheduling, with packet switching and table-driven multicast routing, to bound end-to-end delay for time-constrained traffic, while allowing best-effort traffic to capitalize on the low-latency routing and switching schemes common in modern parallel machines. To limit the cost of servicing time-constrained traffic, the router shares packet buffers and link-scheduling logic between the multiple output ports. Verilog simulations demonstrate that the design meets the performance goals of both traffic classes in a single-chip solution.

关键词： Traffic control Routing Computer architecture Parallel machines Telecommunication traffic Delay Packet switching Concurrent computing Communication networks Throughput

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On task schedulability in real-time control systems

On task schedulability in real-time control systems

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real-time Systems Symposium (RTSS)

作者： D. Seto J.P. Lehoczky L. Sha K.G. Shin Software Engineering Institute Carnegie Mellon University Pittsburgh PA USA Department of Statistics Carnegie Mellon University Pittsburgh PA USA Real-Time Computing Laboratory Department of Electrical Engineering and Computer Sci University of Michigan Ann Arbor MI USA

Most real-time computer-controlled systems are built in two separate steps, each in isolation: controller design and its digital implementation. Computational tasks that realize the control algorithms are usually scheduled by treating their execution times and periods as unchangeable parameters. Task scheduling therefore depends only on the limited computing resources available. On the other hand, controller design is primarily based on the continuous-time dynamics of the physical system being controlled. The set of tasks resulting from this controller design may not be schedulable with the limited computing resources available. Even if the given set of tasks is schedulable, the overall control performance may not be optimal in the sense that they do not make a full use of the computing resource. We propose an integrated approach to controller design and task scheduling. Specifically, task frequencies (or periods) are allowed to vary within a certain range as long as such a change does not affect critical control functions such as maintenance of system stability. We present an algorithm that optimizes task frequencies and then schedules the resulting tasks with the limited computing resources available. The proposed approach is also applicable to failure recovery and reconfiguration in real-time control systems.

关键词： real time systems Control systems Processor scheduling Scheduling algorithm Digital control Dynamic scheduling System performance Application software software engineering Statistics

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Message transmission with timing constraints in ring networks

Message transmission with timing constraints in ring network...

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real-time Systems Symposium (RTSS)

作者： Ching-Chih Han K.G. Shin Department of Electrical Engineering Ohio State Uinversity Columbus OH USA Real-Time Computing Laboratory Department of Elect. Engineering and Computer Science University of Michigan Ann Arbor MI USA

We consider the message transmission problem in unidirectional slotted ring networks. We consider two operation modes: 1) the evacuation mode, in which all messages arrive before system initialization and no new message arrives during system operation; and 2) the continuation mode, in which new messages may arrive after system initialization. We study the performance of several message scheduling policies with respect to three performance measures: meeting all message deadlines, minimizing the maximum delay or the total length of busy periods, and minimizing the average delay. We show that the least-slack-time-first (LSF) scheduling policy is optimal in evacuation mode operation with respect to meeting all message deadlines, while no optimal scheduling policy can possibly exist for continuation mode operation. For the other two performance measures, we show that in the case when messages may be of variable lengths: 1) the farthest-destination-first (FDF) policy is optimal in terms of minimizing the maximum delay and minimizing the total length of busy periods for evacuation mode and for continuation mode operation, respectively, and 2) no optimal scheduling policy can possibly exist in terms of minimizing the average delay under either evacuation mode or continuation mode operation.

关键词： Timing Intelligent networks Length measurement Delay effects Computer architecture Media Access Protocol Scattering Broadcasting Switches Laboratories

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Testing of fault-tolerant and real-time distributed systems via protocol fault injection

Testing of fault-tolerant and real-time distributed systems ...

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International Symposium on Fault-Tolerant computing (FTCS)

作者： S. Dawson F. Jahanian T. Mitton Teck-Lee Tung Real-Time Computing Laboratory Electrical Engineering and Computer Science Department University of Michigan Ann Arbor MI USA Electrical Engineering and Computer Science Department University of Michigan Ann Arbor MI USA

As software for distributed systems becomes more complex, ensuring that a system meets its prescribed specification is a growing challenge that confronts software developers. This is particularly important for distributed applications with strict dependability and timeliness constraints. This paper reports on ORCHESTRA, a portable fault injection environment for testing implementations of distributed protocols. This tool is based on a simple yet powerful framework called script-driven probing and fault injection, for the evaluation and validation of the fault-tolerance and timing characteristics of distributed protocols. The tool, which was initially developed on the real-time Mach operating system and later ported to other platforms including Solaris and SunOS, has been used to conduct extensive experiments on several protocol implementations. This paper describes the design and implementation of the fault injection tool focusing on architectural features to support portability, minimizing intrusiveness on target protocols, and explicit support for testing real-time systems. The paper also describes the experimental evaluation of two protocol implementations: a real-time audio-conferencing application on real-time Mach, and a distributed group membership service on the Sun Solaris operating system.

关键词： System testing Fault tolerant systems real time systems Protocols Operating systems software systems Application software Fault tolerance Timing Sun

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Design and analysis of a WDMA protocol for passive star-coupled lightwave networks

Design and analysis of a WDMA protocol for passive star-coup...

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IEEE Annual Joint Conference: INFOCOM, IEEE Computer and Communications Societies

作者： Chao-Ju Hou Bin Wang Ching-Chih Han Computer Engineering Division Department of Elect. and Comput. Eng. University of Wisconsin Madison WI USA Real-Time Computing Laboratory Department of Elect. Eng. and Comput. Science University of Michigan Ann Arbor MI USA

ISBN: (纸本)0818672935

Based on the POPSMAC protocol proposed in Chung-Sheng Li et al. (1993), we propose an improved medium access protocol for wavelength division multiple access (WDMA) photonic networks. Using the same set of photonic devices as in POPSMAC, the proposed protocol alleviates the drawbacks of the POPSMAC protocol, e.g., invalid data transmissions following receiver collisions and possible acknowledgement packet collisions with header/data packets, while retaining many advantages of POPSMAC. As a result, the network performance in terms of the throughput and the packet delay is improved. Analytical models based on the timing diagram analysis, the continuous-time Markov chain, and the randomization technique are developed to assess the performance of the proposed protocol. The performance is evaluated in terms of channel utilization, mean packet delay, and packet delay distribution with variations in the number of nodes, the offered traffic, the size of data packets, and the network propagation delay. Numerical results show that the proposed protocol achieves better channel utilization and incurs lower packet delays than POPSMAC.

关键词： Access protocols Propagation delay Data communication Optical receivers Throughput Analytical models Timing Performance analysis Telecommunication traffic Traffic control

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PROBING AND FAULT INJECTION OF DEPENDABLE DISTRIBUTED PROTOCOLS

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COMPUTER JOURNAL 1995年第4期38卷 286-300页

作者： DAWSON, S JAHANIAN, F Real-Time Computing Laboratory Electrical Engineering and Computer Science Department University of Michigan Ann Arbor MI 48109-2122 United States

Ensuring that a distributed system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper presents a technique for probing and fault injection of fault-tolerant distributed protocols. The proposed technique, called script-driven probing and fault injection, can be used for studying the behaviour of distributed systems and for detecting design and implementation errors of fault-tolerant protocols. The focus of this work is on fault injection techniques that can be used to demonstrate three aspects of a target protocol: detection of design or implementation errors;identification of violations of protocol specifications;and insight into design decisions made by the implementers. The emphasis of our approach is on experimental techniques intended to identify specific ''problems'' in a protocol or its implementation rather than the evaluation of system dependability through statistical metrics such as fault coverage. To demonstrate the capabilities of this technique, the paper describes a probing and fault injection toot, called the PFI tool (probe/fault injection tool), and a summary of several extensive experiments that studied the behaviour of two protocols: the Transmission Control Protocol (TCP) and a group membership protocol (GMP).

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computing time-DELAY AND ITS EFFECTS ON real-time CONTROL-SYSTEMS

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IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY 1995年第2期3卷 218-224页

作者： SHIN, KG CUI, XZ Real-Time Computing Laboratory Division of Comuuter Science and Engineering. Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The reliability of a real-time digital control computer depends not only on the reliability of the hardware and software used, but also on the time delay in computing the control output, because of the negative effects of computing time delay on control system performance. For a given fixed sampling interval, the effects of computing time delay are classified into the delay and loss problems, The delay problem, occurs when the computing time delay is nonzero but smaller than the sampling interval, while the loss problem occurs when the computing time delay is greater than, or equal to, the sampling interval, i,e., loss of the control output, These two problems are analyzed as a means of evaluating real-time control systems, First, a generic analysis of the effects of computing time delay is presented along with necessary conditions for system stability, Then, we present both qualitative and quantitative analyses of the computing time delay effects on a robot control system, deriving upper bounds of the computing time delay with respect to system stability and system performance.

关键词： Delay effects real time systems Control systems Sampling methods System performance Stability analysis Digital control Hardware software performance Performance analysis

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Deterministic fault injection of distributed systems

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International Workshop on Theory and Practice in Distributed Systems

作者： Dawson, S Jahanian, F Real-Time Computing Laboratory Electrical Engineering and Computer Science Department University of Michigan Ann Arbor 48109-2122 MI United States

ISBN: (纸本)3540600426

Ensuring that a system meets its prescribed specification is a growing challenge that confronts software developers and system engineers. Meeting this challenge is particularly important for distributed systems with strict dependability and timeliness constraints. This paper presents a technique, called script-driven probing and fault injection, for the evaluation and validation of dependable protocols. The proposed approach can be used to demonstrate three aspects of a target protocol: i) detection of design or implementation errors, ii) identification of violations of protocol specifications, and iii) insight into design decisions made by the implementers. To demonstrate the capabilities of this technique, the paper briefly describes a probing and fault injection tool called the PFI tool, and several experiments on two protocols: the Transmission Control Protocol (TCP) [4, 24] and the Group Membership Protocol (GMP) [19]. The tool can be used to delay, drop, reorder, duplicate, and modify messages. It can also introduce new messages into the system to probe participants. In the case of TCP, we used the PFI tool to duplicate the experiments reported in [7] on several TCP implementations without access to the vendors' TCP source code in a very short time. We also ran several new experiments that are difficult to perform using past approaches based on packet monitoring and filtering. In the case of GMP, we used the tool to test the fault-tolerance capabilities of an implementation under various failure models including daemon/link crash, send/receive omissions, and timing failures. Furthermore, by selective reordering of messages and spontaneous transmission of new messages, we were able to guide a distributed computation into hard to reach global states without instrumenting the protocol implementation.

关键词： Transmission control protocol

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PP-MESS-SIM: A simulator for evaluating multicomputer interconnection networks 28

PP-MESS-SIM: A simulator for evaluating multicomputer interc...

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28th Annual Simulation Symposium, ANSS 1995

作者： Rexford, Jennifer Dolter, James Feng, Wu-chang Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)0818670916

This paper presents pp-mess-sim, an object-oriented discrete-event simulation environment for evaluating multicomputer networks. The simulator provides a toolboz of various network topologies, communication workloads, routing-switching algorithms, and router models. These router models can vary from high-level architectures to low-level specification of actual devices. By decoupling individual parts of the code, pp-mess-sim enables independent code development and creates a flexible and extensible environment for evaluating different aspects of network design. Sample simulation experiments capitalize on this flezibility to compare routing-switching schemes under various application workloads. © 1995 IEEE

关键词： Discrete event simulation

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QoS-Sensitive protocol processing in shared-memory multiprocessor multimedia servers 3

QoS-Sensitive protocol processing in shared-memory multiproc...

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3rd IEEE Workshop on the Architecture and Implementation of High Performance Communication Subsystems, HPCS 1995

作者： Mehra, A. Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

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