arXiv subjects

Neil J. Gunther

Publications and source records attributed to Neil J. Gunther.

At least 19 recordsLinked to original sources

arXiv2022

Retrospective Observation of Ball Lightning

Ball lightning is a very rarely observed phenomenon that makes it extremely difficult to characterize scientifically. Eye-witness accounts of ball lightning that describe many features in common have been variously recorded for centuries. This note is an account of my observation of ball lightning almost five decades ago. Although it is mostly a compendium of recalled impressions (no photos or videos), it so happens that certain corroborating information has since become available on the Internet and supports the conclusion that I did indeed observe ball lightning. This note also helps to explain why obtaining hard evidence is even more difficult than is generally assumed. Paradoxically, the inordinate delay between the original observation and this documentation may actually have enhanced its scientific merit.

physics.pop-ph↗

arXiv2020

P = FS: Parallel is Just Fast Serial

We prove that parallel processing with homogeneous processors is logically equivalent to fast serial processing. The reverse proposition can also be used to identify obscure opportunities for applying parallelism. To our knowledge, this theorem has not been previously reported in the queueing theory literature. A plausible explanation is offered for why this might be. The basic homogeneous theorem is also extended to optimizing the latency of heterogenous parallel arrays.

cs.PF↗

arXiv2020

Erlang Redux: An Ansatz Method for Solving the M/M/m Queue

This exposition presents a novel approach to solving an M/M/m queue for the waiting time and the residence time. The motivation comes from an algebraic solution for the residence time of the M/M/1 queue. The key idea is the introduction of an ansatz transformation, defined in terms of the Erlang B function, that avoids the more opaque derivation based on applied probability theory. The only prerequisite is an elementary knowledge of the Poisson distribution, which is already necessary for understanding the M/M/1 queue. The approach described here supersedes our earlier approximate morphing transformation.

cs.PF↗

arXiv2018

Linux-Tomcat Application Performance on Amazon AWS

The need for Linux system administrators to do performance management has returned with a vengeance. Why? The cloud. Resource consumption in the cloud is all about pay-as-you-go. This article shows you how performance models can find the most cost-effective deployment of an application on Amazon's cloud.

cs.PF↗

arXiv2016

How to Emulate Web Traffic Using Standard Load Testing Tools

Conventional load-testing tools are based on a fifty-year old time-share computer paradigm where a finite number of users submit requests and respond in a synchronized fashion. Conversely, modern web traffic is essentially asynchronous and driven by an unknown number of users. This difference presents a conundrum for testing the performance of modern web applications. Even when the difference is recognized, performance engineers often introduce modifications to their test scripts based on folklore or hearsay published in various Internet fora, much of which can lead to wrong results. We present a coherent methodology, based on two fundamental principles, for emulating web traffic using a standard load-test environment.

cs.PF↗

arXiv2012

A Note on Disk Drag Dynamics

The electrical power consumed by typical magnetic hard disk drives (HDD) not only increases linearly with the number of spindles but, more significantly, it increases as very fast power-laws of speed (RPM) and diameter. Since the theoretical basis for this relationship is neither well-known nor readily accessible in the literature, we show how these exponents arise from aerodynamic disk drag and discuss their import for green storage capacity planning.

cs.PF↗

arXiv2011

A Methodology for Optimizing Multithreaded System Scalability on Multi-cores

We show how to quantify scalability with the Universal Scalability Law (USL) by applying it to performance measurements of memcached, J2EE, and Weblogic on multi-core platforms. Since commercial multicores are essentially black-boxes, the accessible performance gains are primarily available at the application level. We also demonstrate how our methodology can identify the most significant performance tuning opportunities to optimize application scalability, as well as providing an easy means for exploring other aspects of the multi-core system design space.

cs.DC↗

arXiv2011

A Note on Parallel Algorithmic Speedup Bounds

A parallel program can be represented as a directed acyclic graph. An important performance bound is the time to execute the critical path through the graph. We show how this performance metric is related to Amdahl speedup and the degree of average parallelism. These bounds formally exclude superlinear performance.

cs.DC↗

arXiv2008

Multidimensional Visualization of Oracle Performance Using Barry007

Most generic performance tools display only system-level performance data using 2-dimensional plots or diagrams and this limits the informational detail that can be displayed. Moreover, a modern relational database system, like Oracle, can concurrently serve thousands of client processes with different workload characteristics, so that generic performance-data displays inevitably hide important information. Drawing on our previous work, this paper demonstrates the application of Barry007 multidimensional visualization to the analysis of Oracle end-user, session-level, performance data, showing both collective trends and individual performance anomalies.

cs.PF↗

arXiv2008

Getting in the Zone for Successful Scalability

The universal scalability law (USL) is an analytic model used to quantify application scaling. It is universal because it subsumes Amdahl's law and Gustafson linearized scaling as special cases. Using simulation, we show: (i) that the USL is equivalent to synchronous queueing in a load-dependent machine repairman model and (ii) how USL, Amdahl's law, and Gustafson scaling can be regarded as boundaries defining three scalability zones. Typical throughput measurements lie across all three zones. Simulation scenarios provide deeper insight into queueing effects and thus provide a clearer indication of which application features should be tuned to get into the optimal performance zone.

cs.PF↗

arXiv2008

A General Theory of Computational Scalability Based on Rational Functions

The universal scalability law of computational capacity is a rational function C_p = P(p)/Q(p) with P(p) a linear polynomial and Q(p) a second-degree polynomial in the number of physical processors p, that has been long used for statistical modeling and prediction of computer system performance. We prove that C_p is equivalent to the synchronous throughput bound for a machine-repairman with state-dependent service rate. Simpler rational functions, such as Amdahl's law and Gustafson speedup, are corollaries of this queue-theoretic bound. C_p is further shown to be both necessary and sufficient for modeling all practical characteristics of computational scalability.

cs.PF↗

arXiv2004

Benchmarking Blunders and Things That Go Bump in the Night

Benchmarking; by which I mean any computer system that is driven by a controlled workload, is the ultimate in performance testing and simulation. Aside from being a form of institutionalized cheating, it also offer countless opportunities for systematic mistakes in the way the workloads are applied and the resulting measurements interpreted. Right test, wrong conclusion is a ubiquitous mistake that happens because test engineers tend to treat data as divine. Such reverence is not only misplaced, it's also a sure ticket to production hell when the application finally goes live. I demonstrate how such mistakes can be avoided by means of two war stories that are real WOPRs. (a) How to resolve benchmark flaws over the psychic hotline and (b) How benchmarks can go flat with too much Java juice. In each case I present simple performance models and show how they can be applied to correctly assess benchmark data.

cs.PF↗

arXiv2004

Characterization of the Burst Stabilization Protocol for the RR/RR CICQ Switch

Input buffered switches with Virtual Output Queueing (VOQ) can be unstable when presented with unbalanced loads. Existing scheduling algorithms, including iSLIP for Input Queued (IQ) switches and Round Robin (RR) for Combined Input and Crossbar Queued (CICQ) switches, exhibit instability for some schedulable loads. We investigate the use of a queue length threshold and bursting mechanism to achieve stability without requiring internal speed-up. An analytical model is developed to prove that the burst stabilization protocol achieves stability and to predict the minimum burst value needed as a function of offered load. The analytical model is shown to have very good agreement with simulation results. These results show the advantage of the RR/RR CICQ switch as a contender for the next generation of high-speed switches.

cs.NI↗

arXiv2002

A New Interpretation of Amdahl's Law and Geometric Scalability

The multiprocessor effect refers to the loss of computing cycles due to processing overhead. Amdahl's law and the Multiprocessing Factor (MPF) are two scaling models used in industry and academia for estimating multiprocessor capacity in the presence of this multiprocessor effect. Both models express different laws of diminishing returns. Amdahl's law identifies diminishing processor capacity with a fixed degree of serialization in the workload, while the MPF model treats it as a constant geometric ratio. The utility of both models for performance evaluation stems from the presence of a single parameter that can be determined easily from a small set of benchmark measurements. This utility, however, is marred by a dilemma. The two models produce different results, especially for large processor configurations that are so important for today's applications. The question naturally arises: Which of these two models is the correct one to use? Ignoring this question merely reduces capacity prediction to arbitrary curve-fitting. Removing the dilemma requires a dynamical interpretation of these scaling models. We present a physical interpretation based on queueing theory and show that Amdahl's law corresponds to synchronous queueing in a bus model while the MPF model belongs to a Coxian server model. The latter exhibits unphysical effects such as sublinear response times hence, we caution against its use for large multiprocessor configurations.

cs.DC↗

arXiv2000

Performance and Scalability Models for a Hypergrowth e-Commerce Web Site

The performance of successful Web-based e-commerce services has all the allure of a roller-coaster ride: accelerated fiscal growth combined with the ever-present danger of running out of server capacity. This chapter presents a case study based on the author's own capacity planning engagement with one of the hottest e-commerce Web sites in the world. Several spreadsheet techniques are presented for forecasting both short-term and long-term trends in the consumption of server capacity. Two new performance metrics are introduced for site planning and procurement: the effective demand, and the doubling period.

cs.PF↗

arXiv2000

A Benchmark for Image Retrieval using Distributed Systems over the Internet: BIRDS-I

The performance of CBIR algorithms is usually measured on an isolated workstation. In a real-world environment the algorithms would only constitute a minor component among the many interacting components. The Internet dramati-cally changes many of the usual assumptions about measuring CBIR performance. Any CBIR benchmark should be designed from a networked systems standpoint. These benchmarks typically introduce communication overhead because the real systems they model are distributed applications. We present our implementation of a client/server benchmark called BIRDS-I to measure image retrieval performance over the Internet. It has been designed with the trend toward the use of small personalized wireless systems in mind. Web-based CBIR implies the use of heteroge-neous image sets, imposing certain constraints on how the images are organized and the type of performance metrics applicable. BIRDS-I only requires controlled human intervention for the compilation of the image collection and none for the generation of ground truth in the measurement of retrieval accuracy. Benchmark image collections need to be evolved incrementally toward the storage of millions of images and that scaleup can only be achieved through the use of computer-aided compilation. Finally, our scoring metric introduces a tightly optimized image-ranking window.

cs.IR↗

arXiv2000

UNIX Resource Managers: Capacity Planning and Resource Issues

The latest implementations of commercial UNIX to offer mainframe style capacity management on enterprise servers include: AIX Workload Manager (WLM), HP-UX Process Resource Manager (PRM), Solaris Resource Manager (SRM), as well as SGI and Compaq. The ability to manage server capacity is achieved by making significant modifications to the standard UNIX operating system so that processes are inherently tied to specific users. Those users, in turn, are granted only a certain fraction of system resources. Resource usage is monitored and compared with each users grant to ensure that the assigned entitlement constraints are met. In this paper, we begin by clearing up some of the confusion that has surrounded the motivation and the terminology behind the new technology. The common theme across each of the commercial implementations is the introduction of the fair-share scheduler. After reviewing some potential performance pitfalls, we present capacity planning guidelines for migrating to automated UNIX resource management.

cs.PF↗

arXiv2000

Seeing the Forest in the Tree: Applying VRML to Mathematical Problems in Number Theory

We show how VRML (Virtual Reality Modeling Language) can provide potentially powerful insight into the 3x + 1 problem via the introduction of a unique geometrical object, called the 'G-cell', akin to a fractal generator. We present an example of a VRML world developed programmatically with the G-cell. The role of VRML as a tool for furthering the understanding the 3x+1 problem is potentially significant for several reasons: a) VRML permits the observer to zoom into the geometric structure at all scales (up to limitations of the computing platform). b) VRML enables rotation to alter comparative visual perspective (similar to Tukey's data-spinning concept). c) VRML facilitates the demonstration of interesting tree features between collaborators on the internet who might otherwise have difficulty conveying their ideas unambiguously. d) VRML promises to reveal any dimensional dependencies among 3x+1 sequences.

cs.MS↗