Chapter 1: Introduction

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Overview

What is computer systems performance evaluation and prediction and why are these techniques necessary in today's world of ever decreasing computer systems cost? To answer these questions requires the computer engineer to understand how all elements of a computer system come into play in realizing a user's application and its implementation, fielding, and maintenance. All aspects of a computer system's lifetime are important when trying to understand issues of performance. It is not sufficient to simply buy the "best" general-purpose computing machine one can find today and then implement the intended application on it. One must consider how the system will fit into an existing computing facility and what the requirements on the computer system are today and what these requirements will be during the computer system's lifetime.

The most important driving factors when designing, building, and fielding a computer system are that it performs the intended function correctly, performs the intended function efficiently, and does so in a cost-effective manner. Therefore, initial design for correctness may often outweigh performance and cost as the driving force. Having said this, it is often the case that computer systems designers think of performance, cost, and correctness interchangeably. They are, however, different. A correct design may not imply one that performs blazingly fast or is very cost effective. This may be due to other considerations-for example, we may need to trade off performance or perfect correctness to save cost per unit. This is more typical of engineering designs. We do not always (if ever) have the luxury of infinite time and budget, allowing one to design, build, and field the most elegant and optimal-performing computer system. Therefore, we need methods to aid us in developing systems where we can trade off these conflicting items in some logical manner. That is what computer systems performance evaluation is and what this book is all about.

The objective of this book is to describe a variety of performance analysis methods that can be applied to the various stages of a computer system's design, construction, fielding, and life-cycle maintenance. The goal is to provide the reader with an understanding of what tools or techniques are best applied within a computer system's life cycle so that the designer can analyze alternatives and select near optimal solutions for each stage of this process. We cannot hope to be exhaustive in our coverage of all aspects of a computer system's design, nor can we do so for each analysis technique available. Our goal is to provide sufficient detail, examples, and references so that an interested reader can know what performance evaluation technique is best to apply, how to apply this technique to some level of sophistication, and where to look for further detailed information on a topic if it is needed. Our intention is to provide more of an in-depth survey so that the reader can understand how all the various concepts and techniques apply to computer systems tradeoff analysis.

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