Manual:Profileinfo.php

Details
Allow users to see the profiling information that are stored in the database.

To save the profiling information in the database (required to use this script), you have to modify StartProfiler.php to use the Profiler class and not the stub profiler which is enabled by default. You will also need to set $wgProfileToDatabase to true in LocalSettings.php to force the profiler to save the informations in the database and apply the maintenance/archives/patch-profiling.sql patch to the database.

To enable the profileinfo.php itself, you'll need to set $wgEnableProfileInfo to true in LocalSettings.php. In MediaWiki 1.16 and earlier you also have to create the AdminSettings.php file (see AdminSettings.sample for more information). See also How to debug.