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Old 04-03-2008, 05:55 AM
Jon Masters
 
Default very common kernel modules slow down the boot process

On Wed, 2008-04-02 at 00:23 -0400, Dave Jones wrote:

<snip comments about time taken in modprobe>

> 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.

All I ever heard was that the maximum difference on boot time was a few
seconds, and given the number of calls to modprobe being made by udev, I
never really considered this a big problem. Kay didn't either because he
built a udev with a minimal modprobe in it and found little difference.

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

However, this is probably worth doing. I'm also willing to consider the
modprobed idea, though I think it'll be more useful to simply make
modprobe part of a library that udev can simply link in directly. I'll
start poking at the former idea (sorting modules.dep and indexing)
first. Incidentally, in fact, we already sort those output files in
RHEL, but that's more of a temporarily hack to make the loading order
predictable when two conflicting PCI IDs are listed in those meta data.

On Wed, 2008-04-02 at 15:12 -0400, Bill Notting wrote:

> Kay started poking at integrating modprobe directly into udev with the
> idea of solving some of this... IIRC it didn't help.

Yeah. It didn't. I'm all ears with regard to suggestions on ways to
improve boot time, but let's first make sure we're 100% convinced where
those problems are. Meanwhile, I'll take Dave's comments on board.

Jon.


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