[PC-BSD Dev] Wild idea to speed up boot process

Claudio L. claudio at hpgcc3.org
Thu Aug 22 11:01:41 PDT 2013

I did some testing on a VM (Virtualbox), and here's what I got:

Total time from BIOS screen to desktop: 45 sec
And this can be broken down in:
Grub+BIOS = 8sec  (includes the 3 second pause in GRUB)
Kernel init = 9sec (From the first kernel text until rc is called)
rc = 9 seconds (of which 2 seconds are to just start the loopback 
network interface)

The rest is the time from the text mode "login" prompt that marks the 
end of rc, to a full desktop, including autologin with 1 second delay, 
using XFCE desktop (on KDE will take a lot longer).

So from bios to rc finished I got 26 seconds, and then 19 seconds more 
to load gdm and the desktop.

Now we are at rc, which only takes 20% of my boot time. The speedup I 
was proposing would only be a fraction of that time, since for example 
starting the loopback network interface locks for 2 seconds (why? it's 
just a loopback, makes no sense).
**Warning** wild assumptions follow:
  Assuming we put about 10 MB of scripts and associated programs in RAM, 
at 100 MB/s sequential speed would be read in 0.1 seconds, versus 4 MB/s 
random which would take 2.5 seconds. So we would save 2.4 seconds 
maximum (in an ideal world).
2.4 seconds out of the 9 seconds in rc is a great improvement! But wait, 
2.4 seconds out of the 45 sec total is only a 5%. I can save more than 
2.4 seconds just by changing the timeout settings in GRUB.

Somehow I thought more time was being used at rc (9 seconds is not a 
lot). So I'm now inclined to trash my idea and forget it. I'm convinced 
it would produce a speedup, but after looking at these numbers I'm also 
convinced is not worth the effort.

Consider this thread closed.
Thanks to all for your input.

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