Hello,
A good friend talked to me about yet another PHP Profiler which has a fairly nice and friendly user interface.
Basically drop an extension on your server, add a plugin to your Chromium browser and you are set to profile your backend straight from the browser \O/
It has been created by SensioLabs, the authors of Symfony Frameworks and looks gorgeous. I think it is worth a look at and figure out whether it works with a HHVM
Homepage: https://blackfire.io/
Review by my friend: http://blog.blackfire.io/pomm-a-two-hours-run-with-blackfire.html