In this talk, we will review FreeBSD’s rtprio(2) and POSIX.1b’s scheduling interfaces and embark on a journey around FreeBSD’s implementation of scheduling priorities. It started with a desire to fix a few apparently simple bugs of rtprio(2) and to add some reasonable features and, one thing leading to another, became an almost complete rewrite of this system call and the POSIX.1b’s interfaces’ implementations, as well as some aspect of the schedulers. We will touch on the most interesting problems that the implementation had, in terms of POSIX compliance, security and consistency, and then explain how we fixed or are fixing them. As of this writing, this project is still a work in progress, with about ~30% of the changes being under review. We will report about its status during the talk.