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Real-time Technology and Applications Symposium

作者： A. Mehra A. Indiresan K.G. Shin Real-time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

This paper focuses on bridging the gap between theory and practice in the management of host CPU and link resources for real-time communication. Using our implementation of real-time channels, a paradigm for real-time communication in packet-switched networks, we illustrate the tradeoff between resource capacity and channel admissibility, which determines the number and type of real-time channels that can be accepted for service and the performance delivered to best-effort traffic. We demonstrate that this tradeoff is affected significantly by the choice of implementation paradigms and the grain at which CPU and link resources are multiplexed amongst active channels. To account for this effect we extend the admission control procedure for real-time channels originally proposed using idealized resource models. Our results show that practical considerations significantly reduce channel admissibility compared to idealized resource models. Further, the optimum choice of multiplexing grain depends on several factors such as resource preemption overheads, the relationship between CPU and link bandwidth, and the interaction between link bandwidth allocation and CPU bandwidth allocation.

关键词： Resource management Bandwidth Channel capacity Channel allocation Delay Laboratories engineering management High-speed networks Quality of service Jitter

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Combined routing and scheduling of concurrent communication traffic in hypercube multicomputers

Combined routing and scheduling of concurrent communication ...

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International Conference on Distributed computing Systems

作者： Bing-Rung Tsai K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

We propose and evaluate low-complexity, low-overhead schemes for distributed message scheduling and routing in binary hypercube multicomputers equipped with a hardware communication adapter at each node. The goal is to optimize the network performance not only for steady traffic flow, but also for concurrent bursty traffic. We comparatively evaluate the performance of different scheduling-coding combinations for several switching methods, such as message switching, circuit switching and virtual cut-through. The evaluation results have indicated that in case of heavy transient traffic, a partially-adaptive routing scheme, when combined with an appropriate message-scheduling policy, can outperform a fully-adaptive routing scheme.

关键词： Routing Hypercubes Telecommunication traffic Switching circuits Communication switching Processor scheduling Multiprocessor interconnection networks Distributed computing Laboratories Hardware

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Structuring communication software for quality-of-service guarantees

Structuring communication software for quality-of-service gu...

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Real-time Systems Symposium (RTSS)

作者： Ashish Mehra A. Indiresan K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

We propose architectural mechanisms for structuring host communication software to provide QoS guarantees. In particular, we present and evaluate a QoS sensitive communication subsystems architecture for end hosts that provides real time communication support for generic network hardware. This architecture provides services for managing communication resources for guaranteed QoS (real time) connections, such as admission control, traffic enforcement, buffer management, and CPU and link scheduling. The design of the architecture is based on three key goals: maintenance of QoS guarantees on a per connection basis, overload protection between established connections, and fairness in delivered performance to best effort traffic. Using this architecture we implement real time channels, a paradigm for real time communication services in packet switched networks. We evaluate the implementation to demonstrate the efficacy with which the architecture maintains QoS guarantees while adhering to the stated design goals. The evaluation also demonstrates the need for specific features and policies provided in the architecture.

关键词： Software quality Quality of service computer architecture Resource management Communication system traffic control Hardware Admission control Protection Packet switching Communication switching

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ORCHESTRA: a probing and fault injection environment for testing protocol implementations

ORCHESTRA: a probing and fault injection environment for tes...

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International computer Performance and Dependability Symposium

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

Ensuring that a distributed system meets its prescribed specification is a growing challenge that confronts software developers and system engineers. Meeting this challenge is particularly important for applications with strict dependability and/or timeliness constraints. We have developed a software fault injection tool, called ORCHESTRA, for testing dependability and timing properties of distributed protocols. ORCHESTRA is based on a simple yet powerful framework, called script-driven probing and fault injection. The emphasis of this 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. Hence, the focus is on developing fault injection techniques that can be employed in studying three aspects of a target protocol: i) detecting design or implementation errors, ii) identifying violations of protocol specifications, and iii) obtaining insights into the design decisions made by the implementers.

关键词： Protocols Fault diagnosis Software systems Power engineering and energy Systems engineering and theory Application software Software tools Software testing Timing Fault detection

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Fault injection experiments on real-time protocols using ORCHESTRA

Fault injection experiments on real-time protocols using ORC...

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IEEE International Symposim on High Assurance Systems engineering

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

The paper presents a set of experiments on real time protocols using the ORCHESTRA software fault injection environment. The paper first describes a specific implementation of ORCHESTRA for testing applications that use Unix sockets for communication. A novel feature of this tool is that it utilizes operating system support provided by Real time Mach to quantify and compensate for the intrusiveness of the fault injection mechanism. The fault injection experiments which are described, tested fault tolerance and timing behavior of two target real time protocols. In addition, timing intrusiveness of ORCHESTRA was measured during the course of these experiments.

关键词： Protocols Timing Probes System testing Delay Application software Sockets Operating systems Real time systems Software measurement

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A Router Architecture for Real-time Point-to-Point Networks

A Router Architecture for Real-Time Point-to-Point Networks

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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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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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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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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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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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