Every game, no matter how old and simple, I run on my computer constantly uses an entire CPU thread even when idling at a menu. (Except for some newer multi-threaded games that do the same with multiple threads!) To raise this from a curiosity to a problem, this means that my computer's fans are on at full blast whenever I have a game going, so I notice.
To be clear, that symptom could be the result of many different
possible causes, others of which I may explore in future blog
posts.1 But specifically for systems with Nvidia GPUs using
the Nvidia proprietary driver (as opposed to
nouveau), setting the environmental variable
USLEEP fixed the issue in some games for me. To do so when running
a single game, run
__GL_YIELD="USLEEP" /path/to/game or
to do so permanently, add the line
~/.profile and restart X.