From a quick skim of the repo it looks to be injecting phptop_hook.php into any call to a php file with auto_prepend_file in php.ini. phptop_hook.php generates

From a quick skim of the repo it looks to be injecting phptop_hook.php into any call to a php file with auto_prepend_file in php.ini. phptop_hook.php generates some stats on how long it took the php file to process and stores this via error_log() which can then be queried with the perl script phptop.