In chapter 23 we learn about measuring performance.
Before you can make your code faster, you first need to figure out what’s making it slow. This sounds easy, but it’s not. Even experienced programmers have a hard time identifying bottlenecks in their code. So instead of relying on your intuition, you should profile your code: measure the run-time of each line of code using realistic inputs.
Once you’ve identified bottlenecks you’ll need to carefully experiment with alternatives to find faster code that is still equivalent. In Chapter 24 (“Improving performance”) you’ll learn a bunch of ways to speed up code, but first you need to learn how to microbenchmark so that you can precisely measure the difference in performance.
“Profiling” shows you how to use profiling tools to dig into exactly what is making code slow. Section “Microbenchmarking” shows how to use microbenchmarking to explore alternative implementations and figure out exactly which one is fastest.