The Zend Developer Zone has posted the theird part of their series (by Stefan Priebsch) about working with XDebug in PHP to profile your applications.

In this week's issue, we will have a look at profiling. Profiling is a feature that seems to be similar to trace logging at first sight. Profiling logs, however, are not meant for human readability, and are not meant to visualize the program's control flow, but provide the data for a statistical analysis of the program run.

He includes an example of the profiling log his XDebug setup is generating and gives the settings you'll need to make a log of your own like php.ini settings to start it up and name it/place it where you want it.

He also talks about the method to get something useful out of the profiling logs - using WinCacheGrind or KCacheGrind to get an overview of what's going on "on the inside" of your application.