very common kernel modules slow down the boot process
Dave Jones
davej at redhat.com
Wed Apr 2 04:23:38 UTC 2008
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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