Booting faster

Stewart Smith

Doing kernel and firmware development leaves you rebooting computers a *lot*. Modern computers (especially servers) take too long to boot.

Since OpenPOWER systems have a fully open firmware stack (some even with an open BMC stack), we can now attack the problem from *all* angles. This talk covers efforts over the past several years into making POWER based systems boot faster. Is it Linux itself that takes the most time? Firmware? What part of firmware and why? Are the problems for a single socket desktop system different to those from an 8 socket enterprise one? Where have we gotten *worse* and why?

Can we go from close to 10 minutes to less than 30 seconds? 10 seconds? At what point are we purely limited by peoples unreasonable expectations of having PCI, RAM, and output on a display?

We go on a full stack deep dive into what it takes to cold (and warm) boot (and reboot) a system - or at least any part of that which takes time, as well as how we've measured it. We'll touch on code before the power button works, code from before the first instruction is executed, and code all the way up to being able to load a kernel off disk and beyond.

When talking about future improvements, anyone stating "but you're already faster than a bunch of our other servers" will be subtly ssshhed.