SW Testing: How do big gaming companies test performance?

Doing automated tests and measuring (profiling et al) or... Inviting the community to use the game i.e. play? In case of gaming it's the latter. You'll be given to experience the privilege of playing the new game months before they are out in the market, and if you are a fan you'll do it for free. In fact you're taking part of the software development life cycle, allowing the engineering team to fine tune the games, the servers settings and more.
Recent example:
https://www.theguardian.com/technology/2017/sep/21/call-of-duty-too-old-shooter-younger-competitors