Avoid the full POST by your BIOS for a slightly faster reboot time, in
append = "reboot=bios,warm"
Brief explanation of options:
bios Use the CPU reboot vector for warm reset warm Don't set the cold reboot flag
Using warm reset will be much faster especially on big memory systems because the BIOS will not go through the memory check. Disadvantage is that not all hardware will be completely reinitialized on reboot so there may be boot problems on some systems.
/usr/src/linux/Documentation/x86/x86_64/boot-options.txt for more details.