After a lot of debugging constant hard freeezes on -CURRENT from the end of Novemeber, iwi0 does not seem to like MPSAFE. Box is back to snappy now.
> uname -a
FreeBSD faith.shanu.net 7.0-CURRENT FreeBSD 7.0-CURRENT #11: Sat Dec 9 11:56:55 IST 2006 email@example.com:/usr/obj/usr/src/sys/MYKERNEL i386
> grep mpsafe /boot/loader.conf.local
At some point in time I do have to report back to -current with the LORs which do turn up with WITNESS and INVARIANTS enabled in the kernel.
See http://www.freebsd.org/smp/ for more on the mpsafe work doing as part of the SMP scaling efforts on FreeBSD