Moblin config kernel initialisation performance

[John Johansen]

Andy Whitcroft wrote:
> One of our goals from UDS was to analyse the kernel initialisation
> performance.  The moblin kernel was measured to initialise in about .9s
> whereas the default Ubuntu kernel was booting in about 1.5s (both on the
> 10v).
> 
> While testing the async_populate_rootfs patches I noted did a little
> experimentation to see what else was slowing boot and comparing the
> configuration for those components to the moblin kernel.  The major costs
> are populate_rootfs, pnpisa_init, piix_init and associated port probes.
> We know that moblin does not use an initramfs, and as we can see below
> isapnp is turned off in their config:
> 
>     config-generic:# CONFIG_ISAPNP is not set
> 
> If I boot my 10v with no initramfs and with isapnp disabled on the
> command line I get a kernel init time of approximatly 0.8s.  In short
> we can account in full for the kernel init performance difference from
> disabling both the initramfs and isapnp.
> 
Right so we have:
populating the initramfs taking about .4s and pnpisa taking some where over .2s

We can speed the initramfs portion up by
  - reducing initramfs size
  - parallelizing populate_rootfs
  - possibly switching to LZO decompression which is faster but at a trade off
    of some size increase

What kind of measures do we have, and how accurate are they, for the boot loader
loading the initramfs and kernel.  So we can evaluate the whether switching to
LZO is a win.

Having not looked at it at all what can we do to improve pnpisa?