XHProf

This module allows you to profile your Drupal application using the XHProf profiler from facebook.

From http://mirror.facebook.net/facebook/xhprof/doc.htm

XHProf is a hierarchical profiler for PHP. It reports function-level call counts and inclusive and exclusive metrics such as wall (elapsed) time, CPU time and memory usage. A function's profile can be broken down by callers or callees. The raw data collection component is implemented in C as a PHP Zend extension called xhprof. XHProf has a simple HTML based user interface (written in PHP). The browser based UI for viewing profiler results makes it easy to view results or to share results with peers. A callgraph image view is also supported.

It also provides a native Drupal UI (as opposed to facebook's original php front end) to view the profiling data. Having this in Drupal provides several advantages:

• Simpler setup
• No need to setup extra vhosts
• Limit access via roles and permissions
• Use alternative storage backends such as MongoDb