Profiling early boot boot

Question

What timekeeping functions should I use if I want to profile the early boot process?

I want to see which drivers take too long to probe/attach/initialize and if there is a way to reduce that amount of time. There may even be earlier parts of boot which are too slow.

Answer 1

Kernel tracing can e.g. be done with ktr(4).

Another option is to use dtrace. Sample scripts for monitoring the kernel can be found in /usr/src/cddl/contrib/dtracetoolkit/Kernel/.