very common kernel modules slow down the boot process

[Dave Jones]

On Wed, Apr 02, 2008 at 05:05:09AM +0200, Dennis Jacobfeuerborn wrote:
 > Harald Hoyer wrote:
 > > Dennis Jacobfeuerborn wrote:
 > >> Harald Hoyer wrote:
 > >>> Compiling these modules, which are loaded on nearly every PC, in the
 > >>> kernel cuts down my boot time from 42s to 32s on my computer:
 > >>>
 > >>> ata_generic
 > >>> ata_piix
 > >> ...
 > >>> sr_mod
 > >>> uhci_hcd
 > >>
 > >> Does the boot time decrease depending on the number of modules you
 > >> include in the kernel? Maybe it's just one or a few modules that make
 > >> up the bulk of that time.
 > >
 > > to be tested. was just a rough guess of the most common modules,
 > > compiled and measured.
 > >
 > >>
 > >> Also should configuring these bits as external modules really have
 > >> this much of an impact on the boot time?
 > >
 > > yep. nash, udev, rc.sysinit.. all wait on module loading
 > 
 > But 10s or 25% of boot time just for loading the modules? That sounds quite 
 > bad. Maybe instead of moving the modules into the kernel it would be better 
 > to find out why exactly the loading takes so long and to look at possible 
 > optimizations.

Almost certainly a lot of it will be spent in parsing /lib/modules/$ver/modules.dep
Will Cohen did some experiments by sorting that file so that all the modules that
he had loaded were at the top of the file.  I forget the exact numbers, but
it made a noticable difference.

I suspect that if modules.dep was sorted and indexed, that lookups could be
made a lot faster than they are now.

	Dave

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