If you have McAfee it is very unfriendly.  You have to go to the control center and turn off the computer protection part (there is also a firewall and something else, maybe spam, I dunno).  There is no gaming mode.  There is supposedly a way to designate certain items as immune from tampering, but I never figured out how to do it, even with technical support.  Avast is the one with the gaming mode.