I am running drupal site with very big count of modules and one of them is admin menu. Every page of site is loading very fast except for page when user first logs in to site. After submitting /user login form. So I debugged with xhprof and noticed that admin menu is rebuilding menu every time user is logging in. Login page loads on average in 30 seconds, which is way too long.
Here is screenshot from xhprof http://prntscr.com/r5lxt I can provide more information if you need.