Mastering Perl, 2nd Edition

Chapter 5. Benchmarking Perl

Tony Hoare’s famous quote goes, “Premature optimization is the root of all evil,” although it doesn’t often come with its setup: “We should forget about small efficiencies, say about 97% of the time.” That is, don’t sweat the small stuff until you need to. In this chapter I show how I can look into my Perl programs to see where the slow parts are. Before I start working to improve the performance of my program, I should check to see what the program is actually doing. Once I know where the slow parts are, I concentrate on those.

Benchmarking Theory

The term benchmark comes from surveyors. They create a physical mark in something to denote a known elevation and use that mark to determine other elevations. Those computed elevations can only be right if the original mark is right. Even if the original mark started off right, it might change because it sunk into the ground, the ground moves because of an earthquake, or global warming redefines the ultimate benchmark we call sea level. Benchmarks are comparisons, not absolutes.

For computers, a benchmark compares the performance of one system against another. They can measure many dimensions, such as time to completion, resource use, network activity, or memory use. Several tools already exist for measuring the parts outside of Perl, so I won’t cover those here. I want to look inside Perl to see what I can find. I want to know if one bit of code is faster or uses less memory, or whatever is important to me. ...