Why does the performance of an application run as root and non-root on Linux differ?

Question

linux

Hello!
There is an application (game server), after launching which you can pull it with the stats command and watch its performance (fps from 0 to 1000).
When running an instance of the app as root, fps fluctuates between 950-970.
When running the same instance of the application from a specially created user, fps fluctuates in the range of 890-910.
It is necessary to ensure that when not running as root, the performance of the application also lies in the range of 950-970. How to achieve this and what affects it?
ulimit -a are identical for both users (including cpu time unlimited). Everything was done under Debian 7.6.

Answer 1

Try changing nice and renice, the default root is less polite.