I have Impossible throttling.

[Paul Johnson]

In this website, the argument is made that newer CPUs will use MORE
energy if the throttling level is set to any value except T0.

http://www.thinkwiki.org/wiki/How_to_make_use_of_Dynamic_Frequency_Scaling

Throttling is "old fashioned", I gather.

I had not bothered with cpuscaling/throttling for about 2 years, so
that claim surprised me and I started checking.  My battery life in
Linux is worse than it is in WinXP on the same laptop, so I figured I
might do better.

I have no trouble adjusting the cpuspeed (or do we say cpufreq these
days?) with the gnome applet "CPU Frequency Scaling Monitor".  I have
experimented with the "ondemand" and "conservative" governors.

The throttling has me puzzled, though.

It appears my Lenovo T61 running Ubuntu 9.04 with kernel
2.6.28-13-generic is in a throttling state T8 that does not exist!


$  sudo cat /proc/acpi/processor/CPU0/throttling

state count:             8
active state:            T8
state available: T0 to T7
states:
    T0:                  100%
    T1:                  88%
    T2:                  75%
    T3:                  63%
    T4:                  50%
    T5:                  38%
    T6:                  25%
    T7:                  13%

What the heck is T8? That appears to be impossible, since the valid
states are T0-T7.

I suspected it meant that throttling was disabled, but no! observe:

# cat /proc/acpi/processor/CPU0/info
processor id:            0
acpi id:                 0
bus mastering control:   yes
power management:        yes
throttling control:      yes
limit interface:         yes



If I want to force the system to always stay in T0, what should I do?
I can't see any way to do this as a nonroot user or with su.

I can get there with

$ sudo su

$ echo 0 > /proc/acpi/processor/CPU0/throttling

I have no actual evidence that this helps, but the ThinkWiki site
claims it will.

Once I learn the "right" setting, I'd like to fix it permanently.

If I knew the correct syntax, I could put it in /etc/sysfs.conf.

Right?


-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas