Valgrind is a entire suite of open-source tools, including basic debugging, profiling, and more advanced techniques such as threading, memory management, and leak detection. For the purposes of this article, I will focus on Cachegrind, and in particular within the domain of Web applications. Although there are a number of developers contributing to Valgrind, Julian Seward is the original designer and author.

He talks about the cachegrind software and the PHP-based profiler that can create these files - XDebug. He also includes a list of a few of the cachegrind viewers including KCachegrind and Webgrind.

Cachegrind provides a nice graphical display of your profiling information but I run Mac OSX [...] What I needed was a way to replicate the old Xdebug 1.x functionality. From this the idea of "PHPGrind" was born. Right now its just a proof of concept but I am hoping with some more understanding of the cachegrind format I can make it into something as useful as the graphical versions.

His application grabs the cachegrind file and processes through it to pull out the events, version information and the target profiled and outputs them in a simple loop at end.

Commentors on the post also suggest Webgrind and MacallGrind.

Xdebug is a PHP extension which helps you to understand, debug and profile PHP. It can help you to find bottlenecks or give you an quick overview what happens in code you aren't familiar with, yet.

The post gives a brief overview of the installation of the extension (building a shared module) and shows how to get started with profiling an application. He talks about the cachegrind tool you can use to parse the results and the kcachegrind app that will make the results a bit more visual.

As a bonus, he also throws in a bit about function tracing - picking out each small bit of functionality in the code (the function/methods) and gathering stats for each.

We were looking for a simple open-source PHP profiler, without any fancy IDEs like Zend bundled together. After a little search, we found one: Xdebug, debugger and profiler tool for PHP.

XDebug is "extension helps you debugging your script by providing a lot of valuable debug information. The debug information that Xdebug can provide includes the following: stack traces, memory allocation and protection for infinite recursions".