On the IBuildings techPortal site today there's a new article (written up by Lorenz Alberton) about using the XHProf profiling tool as an alternative to the feature used in another popular PHP-related too Xdebug.

In this article, we're going to try another profiler, XHProf, developed at Facebook and open sourced in March 2009 (under the Apache 2.0 license). XHProf is a function-level hierarchical profiler, with a PHP extension (written in C) to collect the raw data, and a few PHP scripts for the reporting/UI layer.

He walks you through the install (either via packages or, if it complains, via the usual PECL build process) and the functions you'd need to profile a chunk of code, an entire page and how to use the UI and reporting output to help define where the real problems are in your code.