Moblin config kernel initialisation performance

[Andy Whitcroft]

On Wed, Dec 02, 2009 at 02:40:45PM -0800, John Johansen wrote:

> 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

I am relying on you to help us out making the initramfs smaller.
csurbhi has some promising work to async'ise the populate_rootfs part.

> 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.

None that I am aware of as its before we see time.  There was some
rumours we could get grub2 to pass a 'I started at this tsc tick' or
something to allow the kernel to work out the delta.

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

A lot of the time is in the form of 'send this' 'wait 250us' 'read
that', loops which must be repeated to scan for and find pnp devices.
Its not clear how much this can be improved.

I am hoping we can avoid needing to by the speed ups in initramfs both
in unpack and run time.

-apw