About Performance

"My program is not fast enough. Users are saying that it is not performing well. What can I do?"

These are the words I hear a lot when consulting on different programming projects. Sometimes the answer is simple, sometimes hard, but almost always the critical part of the answer lies in the question. More specifically, in one word - performing.

What do we mean when we say that a program is performing well? Actually, nobody cares. What we have to know is what users mean when they say that the program is not performing well. And users, you'll probably admit, look at the world in a very different way than we programmers.

Before starting to measure and improve the performance of a program, we have to find out what users really mean by the word performance. Only then can we do something productive about it.

We will cover the following topics in this chapter:

• What is performance?
• What do we mean when we say that a program performs well?
• What can we tell about the code speed by looking at the algorithm?
• How does the knowledge of compiler internals help us write fast programs?
• Why is it better to measure than to guess?
• What tools can we use to find the slow parts of a program?