[gentoo-dev] Why is preempt-kernel *required* for building a kernel using gentoo-sources ?

[Dan Naumov]

Hey.

I just stubled across a very weird problem. I was told that using preempt slows down SETI so I decided to do some benchmarking to see whether it's true. I loaded my kernel config, disabled preempt and ran  "make dep clean bzImage modules modules_install", the build failed with:

fs/fs.o: In function `dput':
fs/fs.o(.text+0x11ff5): undefined reference to `atomic_dec_and_lock'
make: *** [vmlinux] Error 1

I go back to menuconfig, add preempt kernel back, save config, recompile again and it works...how come ? Changing the compile optimisations doesn not seem to have any effect on this... According to a thread on Gentoo Forums (http://forums.gentoo.org/viewtopic.php?t=3915), I am not the only have having the problem either.

Sincerely,
Dan Naumov