readahead_early.

[Eric Sandeen]

Dave Jones wrote:
> Right now we're running readahead early way too late.
> At a time when we've just sat doing no IO at all for 10
> seconds whilst (amongst other things) we waited for a
> DHCP lease.   We're also running it at a time when
> we're competing for disk bandwidth with other processes.
> The result is that disabling the service completely shows
> no change in boot time at all.
> http://www.codemonkey.org.uk/junk/bootchart-before.png
> 
> Moving the readahead_early service to start really early
> wins back 4 seconds of boot up time.
> http://www.codemonkey.org.uk/junk/bootchart-after.png

FWIW, on my test box, entirely *disabling* readahead saves 2-4 seconds
on boot time... :)

-Eric