http://www.netbsd.org/~xtraeme/p4tcc.diff
   
   BTW, I added in arch/x86 because some Pentium 4 models have
   the EM64T extension, so that you can run it with NetBSD/amd64
   (this is my case).
   
   Any comment before I commit this?


this patch should be optional and disabled by default.  in 
testing on P4-M 2.2 systems i was able to only observe less
than 1W usage drop when setting my clock mod to the lowest
availble.  that's reducing my cpu speed to 1/8th (275mhz
effectively.)  when switching (old) speedstep from 2.2ghz
to 1.2ghz i observed 5-6W benefit.

at the time i discussed with some x86 folks i know and other
information i found on the web indicated that my results
were to be expected.  ie, p4 clock modulation is pretty 
useless as a power saving feature, and i believe people
should have to choose to enable it.


i just found the patch i wrote for this back then:
http://mail-index.netbsd.org/port-i386/2004/08/17/0002.html
it makes me realise me that your code is also not MP
friendly.  it will run p4tcc_init() ncpu times on cpu0.


.mrg.