Yocto Rocko 2.4.1 is: OE-Core, meta-yocto and Bitbake (and yocto-docs but yocto-docs contains no functionality) without 7 files.
gits @ SHAs
OE-Core from https://github.com/openembedded/openembedded-core.git @ 9d1129076658b4c5827c95ad8b195a7a100d7a9e
This post lists the efficiency of Linux Kernel development using Yocto. It shows that developers who use Yocto to do kernel development spend at least 75% of their recompile time waiting on the Yocto build system.