printk() has been the tool for debugging the Linux kernel and for being the display mechanism for Linux as long as Linux has been around. It's the first thing one sees as the life of the kernel begins, from the kernel banner and the last message at shutdown. It's critical as people take pictures of a kernel oops to send to the kernel developers to fix a bug, or to display on social media when that oops happens on the monitor on the back of an airplane seat in front of you.
But printk() is not a trivial utility. It serves many functionalities and some of them can be conflicting. Today with Linux running on machines with hundreds of CPUs, printk() can actually be the cause of live locks. This talk will discuss the history of printk, how it's grown, issues that have come about it, and why it is a pain that it is today.
