AFAIC http://www.open.ac.uk/blogs/XHProf/wp-content/uploads/2010/08/profiler.zip only supports sqlite and pgsql (see dbconn.inc.php). Am I right in assuming that there is no MySQL support?
P.S. Separated from the thread "poor performance for logged in users" https://moodle.org/mod/forum/discuss.php?d=222627#p970269.
I think its best to ignore the OU link, since that dates from before Moodle had its own integrated XHProf.
The Moodle integration comes out of the box and will work mysql, you only need to ensure that the XHProf php extension is installed and then enabling profiling.
One thing to watch out for on mysql is ensuring that max_packet_size is large enough because IIRC it stores the profiling data in the database.
Let us know how you get on?