Thought about speeding up startup...

[Matt Zimmerman]

(following up to ubuntu-devel; this is development material)

On Thu, Oct 21, 2004 at 05:26:17PM -0400, Michael S. Jessop wrote:

> ...well, I ran it by someone else first, and they said I didn't sound
> like a total fool... so I'll just cut and paste my original message here
> and see what people think... be nice.  :)
> 
> > In regards to Hotplug and long startups... would it be possible to
> > preconfigure the hardware (hotplug it once, record the results and
> > somehow make the results static) at installation?  You would, of
> course,
> > have to allow for manual scanning of hardware and changes that would
> > require modules to be loaded or not, and also a way to to it with
> > upgrades or installations (flag stuff somehow)?

This basically amounts to a cache, which is a good starting point for many
types of performance problems.  The trick is how to invalidate the cache.
We would need some way of knowing whether hotplug would do something
different if it were allowed to run its course.

Some ideas:

- Store, as part of the process of initializing hotplug, information about
  which device was handled, and cache the result of each individual hotplug
  event based on that (plus some sort of hash of the hotplug configuration).

- Store the entire list of actions taken, and a list of the hotplug-capable
  devices present on the system.  Execute the stored actions unless the list
  of devices has changed.

-- 
 - mdz