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Proceedings of the 1997 ACM sigmetrics international conference on measurement and modeling of computer systems

作者： Erich Nahum David Yates Jim Kurose Don Towsley Department of Computer Science University of Massachusetts Amherst MA

ISBN: (纸本)9780897919098

In this paper we present a performance study of memory reference behavior in network protocol processing, using an Internet-based protocol stack implemented in the x-kernel running in user space on a MIPS R4400-based Silicon Graphics machine. We use the protocols to drive a validated execution-driven architectural simulator of our machine. We characterize the behavior of network protocol processing, deriving statistics such as cache miss rates and percentage of time spent waiting for memory. We also determine how sensitive protocol processing is to the architectural environment, varying factors such as cache size and associativity, and predict performance on future *** show that network protocol cache behavior varies widely, with miss rates ranging from 0 to 28 percent, depending on the scenario. We find instruction cache behavior has the greatest effect on protocol latency under most cases, and that cold cache behavior is very different from warm cache behavior. We demonstrate the upper bounds on performance that can be expected by improving memory behavior, and the impact of features such as associativity and larger cache sizes. In particular, we find that TCP is more sensitive to cache behavior than UDP, gaining larger benefits from improved associativity and bigger caches. We predict that network protocols will scale well with CPU speeds in the future.

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File server scaling with network-attached secure disks 97

File server scaling with network-attached secure disks

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Proceedings of the 1997 ACM sigmetrics international conference on measurement and modeling of computer systems

作者： Garth A. Gibson David F. Nagle Khalil Amiri Fay W. Chang Eugene M. Feinberg Howard Gobioff Chen Lee Berend Ozceri Erik Riedel David Rochberg Jim Zelenka School of Computer Science Carnegie Mellon University Pittsburgh PA Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh PA

ISBN: (纸本)9780897919098

By providing direct data transfer between storage and client, network-attached storage devices have the potential to improve scalability for existing distributed file systems (by removing the server as a bottleneck) and bandwidth for new parallel and distributed file systems (through network striping and more efficient data paths). Together, these advantages influence a large enough fraction of the storage market to make commodity network-attached storage feasible. Realizing the technology's full potential requires careful consideration across a wide range of file system, networking and security issues. This paper contrasts two network-attached storage architectures---(1) Networked SCSI disks (NetSCSI) are network-attached storage devices with minimal changes from the familiar SCSI interface, while (2) Network-Attached Secure Disks (NASD) are drives that support independent client access to drive object services. To estimate the potential performance benefits of these architectures, we develop an analytic model and perform trace-driven replay experiments based on AFS and NFS traces. Our results suggest that NetSCSI can reduce file server load during a burst of NFS or AFS activity by about 30%. With the NASD architecture, server load (during burst activity) can be reduced by a factor of up to five for AFS and up to ten for NFS.

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Multi Robot Trajectory Generation for Single Source Explosion Parameter Estimation

Multi Robot Trajectory Generation for Single Source Explosio...

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IEEE international conference on Robotics and Automation (ICRA)

作者： V.N. Christopoulos S. Roumeliotis Department of Computer Science & Engineering University of Minnesota Minneapolis MN USA

This paper addresses the problem of estimating the parameters of the advection-diffusion equation, which describes the propagation of an instantaneously released gas. A team of mobile robots, equipped with appropriate sensing devices, are used for collecting gas concentration measurements. In addition, each of the robots has sensitive anemometric vanes for determining the velocity and the direction of the wind. The selection of the sequence of locations, where the robot should go to collect the gas concentration measurements, is performed in real-time and is based on the minimization of the uncertainty of the estimated parameters and on reducing the time to convergence of this estimation problem. Simulation results are presented in order to confirm the described approach, which has significantly lower computational requirements than other well-known techniques based on exhaustive global search.

关键词： Explosions Parameter estimation Robot sensing systems Equations Mobile robots Blades Time measurement Performance evaluation Convergence Computational modeling

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The effects of wide-area conditions on WWW server performance 01

The effects of wide-area conditions on WWW server performanc...

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Proceedings of the 2001 ACM sigmetrics international conference on measurement and modeling of computer systems

作者： Erich M. Nahum Marcel-Catalin Rosu Srinivasan Seshan Jussara Almeida Networked Systems Department IBM T.J. Watson Research Ctr. Yorktown Heights NY Dept. of Computer Science Carnegie-Mellon Univ. Pittsburgh PA Dept. of Computer Science University of Wisconsin Madison WI

ISBN: (纸本)9781581133349

WWW workload generators are used to evaluate web server performance, and thus have a large impact on what performance optimizations are applied to servers. However, current benchmarks ignore a crucial component: how these servers perform in the environment in which they are intended to be used, namely the wide-area *** paper shows how WAN conditions can affect WWW server performance. We examine these effects using an experimental test-bed which emulates WAN characteristics in a live setting, by introducing factors such as delay and packet loss in a controlled and reproducible fashion. We study how these factors interact with the host TCP implementation and what influence they have on web server performance. We demonstrate that when more realistic wide-area conditions are introduced, servers exhibit very different performance properties and scaling behaviors, which are not exposed by existing benchmarks running on LANs. We show that observed throughputs can give misleading information about server performance, and thus find that maximum throughput, or capacity, is a more useful metric. We find that packet losses can reduce server capacity by as much as 50 percent and increase response time as seen by the client. We show that using TCP SACK can reduce client response time, without reducing server capacity.

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Blur identification based on kurtosis minimization

Blur identification based on kurtosis minimization

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IEEE international conference on Image Processing

作者： Dalong Li R.M. Mersereau S. Simske School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta GA USA Hewlett-Packard Laboratories Imaging Systems Laboratory Fort Collins CO USA

In this paper, we describe an algorithm for identifying a parametrically described blur based on kurtosis minimization. Using different choices for the parameters of the blur, the noisy blurred image is restored using Wiener filter. We use the kurtosis as a measurement of the quality of the restored image. From the set of the candidate deblurred images, the one with the minimum kurtosis is selected. The proposed technique is tested in a simulated experiment on a variety of blurs including atmospheric turbulence blurs, Gaussian blurs, and out-of-focus blurs. The proposed approach is also tested on real blurred images. Moreover, we test the performance when a wrong blur model is given. Our experiments show that the kurtosis minimization measurements match well with methods that maximize PSNR.

关键词： Image restoration Degradation Deconvolution Testing PSNR Laboratories Minimization methods Atmospheric measurements Atmospheric modeling Convolution

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Performance debugging shared memory parallel programs using run-time dependence analysis 97

Performance debugging shared memory parallel programs using ...

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Proceedings of the 1997 ACM sigmetrics international conference on measurement and modeling of computer systems

作者： Ramakrishnan Rajamony Alan L. Cox Departments of Electrical & Computer Engineering Rice University Houston TX Departments of Electrical & Computer Science Rice University Houston TX

ISBN: (纸本)9780897919098

We describe a new approach to performance debugging that focuses on automatically identifying computation transformations to reduce synchronization and communication. By grouping writes together into equivalence classes, we are able to tractably collect information from long-running programs. Our performance debugger analyzes this information and suggests computation transformations in terms of the source code. We present the transformations suggested by the debugger on a suite of four applications. For Barnes-Hut and Shallow, implementing the debugger suggestions improved the performance by a factor of 1.32 and 34 times respectively on an 8-processor IBM SP2. For Ocean, our debugger identified excess synchronization that did not have a significant impact on performance. ILINK, a genetic linkage analysis program widely used by geneticists, is already well optimized. We use it only to demonstrate the feasibility of our approach to long-running *** also give details on how our approach can be implemented. We use novel techniques to convert control dependences to data dependences, and to compute the source operands of stores. We report on the impact of our instrumentation on the same application suite we use for performance debugging. The instrumentation slows down the execution by a factor of between 4 and 169 times. The log files produced during execution were all less than 2.5 Mbytes in size.

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Blocking in large mobile cellular networks with bursty traffic 01

Blocking in large mobile cellular networks with bursty traff...

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Proceedings of the 2001 ACM sigmetrics international conference on measurement and modeling of computer systems

作者： Nidhi Hegde Khosrow Sohraby Lucent Technologies Bell Laboratories 791 Holmdel-keyport Road Holmdel NJ and Computer Science Telecommunications University of Missouri-Kansas City 5100 Rockhill Road Kansas City MO Computer Science Telecommunications University of Missouri-Kansas City 5100 Rockhill Road Kansas City MO

ISBN: (纸本)9781581133349

We consider large cellular networks. The traffic entering the network is assumed to be correlated in both space and time. The space dependency captures the possible correlation between the arrivals to different nodes in the network, while the time dependency captures the time correlation between arrivals to each node. We model such traffic with a Markov-Modulated Poisson Process(MMPP).It is shown that even in the single node environment, the problem is not mathematically tractable. A model with an infinite number of circuits is used to approximate the finite model. A novel recursive methodology is introduced in finding the joint moments of the number of busy circuits in different cells in the network leading to accurate determination of blocking probability. A simple mixed-Poisson distribution is introduced as an accurate approximation of the distribution of the number ofbusy *** show that for certain cases, in the system with an infinite number of circuits in each cell, there is no effect of mobility on the performance of the system. Our numerical results indicate that the traffic burstiness has a major impact on the system performance. The mixed-Poisson approximation is found to be a very good fit to the exact finite model. The performance of this approximation using few moments is affected by traffic burstiness and average load. We find that in a reasonable range of traffic burstiness, the mixed-Poisson distribution provides a close approximation.

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Adaptive sampling for environmental field estimation using robotic sensors

Adaptive sampling for environmental field estimation using r...

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2005 IEEE/RSJ international conference on Intelligent Robots and systems

作者： M. Rahimi M. Hansen W.J. Kaiser G.S. Sukhatme D. Estrin Center for Embedded Networked Sensing UCLA Los Angeles CA USA Department of Computer Science USC Los Angeles CA USA Department of Computer Science UCLA Los Angeles CA USA

Monitoring environmental phenomena by distributed sensor sampling confronts the challenge of unpredictable variability in the spatial distribution of phenomena often coupled with demands for a high spatial sampling rate. The introduction of actuation-enabled robotics sensors permits a system to optimize the sampling distribution through runtime adaptation. However, such systems must efficiently dispense sampling points or otherwise suffer from poor temporal response. In this paper, we propose and characterize an active modeling system. In our approach, as the robotic sensor acquires measurement samples of the environment, it builds a model of the phenomenon. Our algorithm is based on an incremental optimization process where the robot supports a continuous, iterative process of 1) collecting samples with maximal coverage in the design space; 2) building the environmental model; 3) predicting sampling point locations that contribute the greatest certainty regarding the phenomenon; and 4) sampling the environment based on a combined measure of information gain and navigation and sampling cost. This can provide significant reductions in the magnitude of field estimation error with a modest navigational trajectory time. We evaluate our algorithm through a simulation, using a combination of static and mobile sensors sampling light illumination field.

关键词： Sampling methods Robot sensing systems Sensor phenomena and characterization Orbital robotics Navigation Monitoring Sensor systems Runtime Iterative algorithms Design optimization

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Bounding of performance measures for a threshold-based queueing system with hysteresis 97

Bounding of performance measures for a threshold-based queue...

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Proceedings of the 1997 ACM sigmetrics international conference on measurement and modeling of computer systems

作者： Leana Golubchik John C. S. Lui Columbia University Department of Computer Science The Chinese University of Hong Kong Department of Computer Science & Engineering

ISBN: (纸本)9780897919098

In this paper, we consider a K-server threshold-based queueing system with hysteresis in which the number of servers, employed for servicing customers, is governed by a forward threshold vector F= (F1, F2, …, FK-1) (where F1 < F2 < … < FK-1) and a reverse threshold vector R= (R1, R2, …, RK-1) (where R1 < R2 < … < RK-1). There are many applications where a threshold-based queueing system can be of great use. The main motivation for using a threshold-based approach in such applications is that they incur significant server setup, usage, and removal costs. And, as in most practical situations, an important concern is not only the system performance but rather its cost/performance ratio. The motivation for use of hysteresis is to control the cost during momentary fluctuations in workload. An important and distinguishing characteristic of our work is that in our model we consider the time to add a server to be non-negligible. This is a more accurate model, for many applications, than previously considered in other works. Our main goal in this work is to develop an efficient method for computing the steady state probabilities of a multi-server threshold queueing system with hysteresis, which will, in turn, allow computation of various performance measures.

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Group-guaranteed channel capacity in multimedia storage servers

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Performance Evaluation Review 1997年第1期25卷 285-297页

作者： Tsiolis, Athanassios K. Vernon, Mary K. Univ of Wisconsin-Madison Madison United States

One of the open questions in the design of multimedia storage servers is in what order to serve incoming requests. Given the capability provided by the disk layout and scheduling algorithms to serve multiple streams simultaneously, improved request scheduling algorithms can reduce customer waiting times. This results in better service and/or lower customer loss. In this paper we define a new class of request scheduling algorithms, called Group-Guaranteed Server Capacity (GGSC), that preassign server channel capacity to groups of objects. We also define a particular formal method for computing the assigned capacities to achieve a given performance objective. We observe that the FCFS policy can provide the precise time of service to incoming customer requests. Under this assumption, we compare the performance of one of the new GGSC algorithms, GGSCW-FCFS, against FCFS and against two other recently proposed scheduling algorithms: Maximum Factored Queue length (MFQ), and the FCFS-n algorithm that preassigns capacity only to each of the n most popular objects. The algorithms are compared for both competitive market and captured audience environments. Key findings of the algorithm comparisons are that: (1) FCFS-n has no advantage over FCFS if FCFS gives time of service guarantees to arriving customers, (2) FCFS and GGSCW-FCFS are superior to MFQ for both competitive and captive audience environments, (3) for competitive servers that are configured for customer loss less than 10%, FCFS is superior to all other algorithms examined in this paper, and (4) for captive audience environments that have objects with variable playback length, GGSCW-FCFS is the most promising of the policies considered in this paper. The conclusions for FCFS-n and MFQ differ from previous work because we focus on competitive environments with customer loss under 10%, we assume FCFS can provide time of service guarantees to all arriving customers, and we consider the distribution of customer waiting

关键词： Interactive computer systems

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