On Apr 1, 2008, at 7:22 PM, 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:
It's pretty well known that modprobe is slow. Heck, you've reported
bugs about this before:
https://bugzilla.redhat.com/show_bug.cgi?id=249270 - modprobe is slow
Will Cohen (here at Red Hat) did some profiling and found one of the
major problems was that modprobe takes a long time to search /lib/
modules/`uname -r`/modules.deps:
http://sourceware.org/ml/systemtap/2007-q1/msg00140.html
IIRC one of the proposed solutions was to have 'modprobed' - a
modprobe daemon which would read modules.deps at system startup and
handle all subsequent modprobe requests from udev etc.
Mac OS X does a similar thing; see
http://www.osxbook.com/book/bonus/misc/optimizations/#TWO
and its man pages for kextd(8) and kextcache(8).
The way they do early boot (the parts in our kernel & initrd) is
essentially the same as us. One interesting optimization is that they
support booting from a 'kernelcache' - a big fat image that has the
kernel with the modules needed to find the root device *already linked
in*. Weird. Other than that, as far as I can tell, it's basically just
a kernel+initrd with modules in it.
Once they're into the full system, they start up kextd, which loads
kernel module metadata and handles all further requests for module
loading.
We, on the other hand, re-read the entire module dependency list every
time anything requests a module be loaded. Which happens a *lot* at
system startup. Yuck.
So, yes. There's a fun summer project for someone: modprobed.
-w
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