[clug] ARS: Ubuntu 9.10 boot optimizations: 5 second startup with an SSD
alexsatrapa at mac.com
Thu Oct 1 18:14:39 MDT 2009
On 02/10/2009, at 08:30 , David Schoen wrote:
> Back when I still used Gentoo someone implemented a parallel boot ...
> If Ubuntu can do it in such a way that it works well enough first time
> around it may actually be adopted by the masses.
There was an article about very short boot times: http://lwn.net/Articles/299483/
1) Strip kernel down to absolute minimum needed to boot and launch init
2) Strip init-launched services down to Dbus, stripped-down X,
sReadahead, HAL, udev, networking
3) Work to a blocks-read-in budget of 5 seconds x (disk read from
4) Profile the system startup and put the most interesting blocks into
the cache file used by sReadahead
5) Use a fast disk to boot
The modified version of X includes not invoking the C complier every
time it boots (ie: use the keyboard mappings that worked the last time
you booted this hardware).
They also boot directly into a user's desktop, since the budget was 5
seconds to boot a usable system. They also wanted to avoid "dirty
tricks" like booting the user's desktop and continuing to start
services (ie: heavily load the system) in the background.
I'll add here my observation that "sleep" or "hibernate" actually
takes longer to boot since you're potentially reading all of RAM from
disk (eg: if you have 4GB of RAM, and a disk that handles 30MB/s,
you'll be waiting a touch over 2 minutes to wake from hibernate).
There was another article I was reading by someone who suggested that
if you could make your applications all able to recover cleanly from a
crash (ie: save the do/undo buffer to disk regularly), it would
actually be more sensible to simply "crash to sleep" and reboot from
scratch when you wake the computer. After all, what's the point of
writing all the buffers and cache from memory out to the hibernate
file? Fsync, then stop the processor - save two minutes of battery
life every time the user closes the lid.
A 5 second boot is not using parallel booting. Parallel booting
reduces a 1 minute boot time to 30 seconds - the bottleneck is reading
heaps of redundant data from disk.
Hope this helps.
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