Fast_boot

Fast_boot:
1.http://elinux.org/Deferred_Initcalls
echo 1 > /proc/deferred_initcalls
2.https://www.elinux.org/Boot_Time
3.CONFIG_CC_OPTIMIZE_FOR_SIZE
4.https://elinux.org/Disable_Console#Projects
Disable Consoles
5.Disabled PTYS saved 0.64 s.
6.precalibrates a delay loop(lpj) can save 180ms
7.http://en.wikipedia.org/wiki/Ltrace APP (measure time)