This guide has been take from G-Hacks Blog and quoted has is. If you need more info you should visit the blog following the link in the bottom:
How this works
When you boot up your machine Grub does a search for all the necessary drivers to load. This takes time. Instead of making Grub search for these drivers, the profiling actually makes Grub remember every driver necessary to work, thereby cutting down all of the driver load times.
This is a proven technique that can help the boot process. It has actually been around since Ubuntu 6.04, so it has been tested and tested and does work. I will make this normal disclaimer. Even though Grub profile works, anytime you deal with your bootloader you take the chance that you can render your machine unbootable. So you use this tool at your own risk. Don’t take that to mean profile is a dangerous tool and your machine will wind up bricked and mocking you…that is just to say should something happen, you were warned.
How to add profiling
To do this you are going to have to modify your /etc/default/grub file. The edits are not challenging at all. So, open up a terminal window and get ready to work.
The line you are looking for is:
This is the line that gives the options to Grup upon boot. You need to add one more option to that line so it now looks like:
GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash profile”
Save that file and then issue the command:
You are ready to reboot your machine.
During this next boot time you will see a noticeable SLOW DOWN. This is normal because Grub is now running the profile. This is quite necessary.
Once the boot up is complete, open up that /etc/default/grub file, remove the profile entry you just added, and re-run the command sudo update-grub2. Now reboot your machine again and see if you don’t notice a distinct speed increase in your boot times.
Source: GHacks Blog