[ltp] undervolting centrino via kernel patch or msr module?

[Jiang Qian]

Hi All:
For all the kernel/hardware guru out there, this is a question out of 
curiosity instead of necessity.  I'm a happy user of centrino 
undervolting patch from linux phc
http://linux-phc.sourceforge.net/
This requires me to patch my kernel but I can change cpu voltage without 
rebooting.

However recently I came across this website:
http://www.tuxamito.com.es/cpupw/
which points to the linux msr modules. From what I read of this program 
use msr modules to interface cpu and is able to change the cpu voltage, 
too, apparently *without* kernel patch. However when I attempt the 
change cpu voltage using
./cpupw -V 0 25
and then do
./cpupw --status
it shows the cpu voltage changed, but this change does *not* show up if 
I do:
cat /sys/devices/system/cpu/cpu0/cpufreq/op_points_table

Conversely, however, if I change cpu voltage by changing the voltage 
table at
/sys/devices/system/cpu/cpu0/cpufreq/op_points_table
then do
./cpupw --status
shows changed cpu voltage.

Which one is actually effective? Is it that the cpupw actually change 
the voltage but is not reflected in cpu-voltage table from the kernel 
patch?  Or is it the cpupw does not actually change the cpu voltage?

Thanks a lot for your enlightenment.

Jiang