perf
lttng
http://www.embedded-bits.co.uk/2015/understanding-io-wait-why-no-idle-can-be-ok/
http://lists.denx.de/pipermail/u-boot/2011-April/091481.html
http://free-electrons.com/services/boot-time/
http://free-electrons.com/doc/training/boot-time/
https://wiki.ubuntu.com/BootCharting
http://btorpey.github.io/blog/2014/02/18/clock-sources-in-linux/