ACPI Throttling on Inspiron 5100

As the Dell Insprion 5100 has a standard desktop P4 processor it doesn't support power management but I am experimenting with ACPI throttling to extend battery power life/reduce temperature.  Here's the output from x86info:

wendy:~ # x86info
x86info v1.10.  Dave Jones 2001, 2002
Feedback to <davej@suse.de>.Found 1 CPU
Family: 15 Model: 2 Stepping: 7 Type: 0 [Pentium 4 (Northwood) [C1] Original OEM]
Processor name string:               Intel(R) Pentium(R) 4 CPU 2.66GHz

You can prove this yourself by the following:

wendy:~ # cat /proc/acpi/processor/CPU0/info

processor id:            0

acpi id:                 0

bus mastering control:   yes

power management:        no

throttling control:      yes

limit interface:         yes

You notice the power management: no in the above output No CPU power management Im afraid.  This is further proven because the performance file is missing:

wendy:~ # cat /proc/acpi/processor/CPU0/performance

cat: /proc/acpi/processor/CPU0/performance: No such file or directory

Also there is only one powerstate supported in the power file:

wendy:~ # cat /proc/acpi/processor/CPU0/power

active state:            C1

default state:           C1

bus master activity:     00000000

states:

   *C1:                  promotion[--] demotion[--] latency[000] usage[00000000]

    C2:                 

    C3:                 

However, going back to the output from /proc/acpi/processor/CPU0/info youll notice that throttling is supported.  This is also proven by the output of /proc/acpi/processor/CPU0/throttling:

wendy:~ # cat /proc/acpi/processor/CPU0/throttling

state count:             8

active state:            T0

states:

   *T0:                  00%

    T1:                  12%

    T2:                  25%

    T3:                  37%

    T4:                  50%

    T5:                  62%

    T6:                  75%

    T7:                  87%

Notice the * before T0.  This indicates that there is 00% throttle on the processor, i.e. its running at 100%.  If we change this to anything between T1-T7 we can reduce the processor from running quite so fast:

T0         100%    2.66GHz

T1         88%      2.34GHz

T2         75%      2GHz

T3         63%      1.68GHz

T4         50%      1.33GHz

T5         38%      1.01GHz

T6         25%      665MHz

T7         13%      346MHz

Ive tested this by running xscreensaver and observing a visible slowdown.  I have not done any testing on thermal or battery effects Let me know if you do!

wendy:~ # cat /proc/acpi/processor/CPU0/throttling

state count:             8

active state:            T0

states:

   *T0:                  00%

    T1:                  12%

    T2:                  25%

    T3:                  37%

    T4:                  50%

    T5:                  62%

    T6:                  75%

    T7:                  87%

wendy:~ # echo -n 4 > /proc/acpi/processor/CPU0/throttling

wendy:~ # cat /proc/acpi/processor/CPU0/throttling

state count:             8

active state:            T4

states:

    T0:                  00%

    T1:                  12%

    T2:                  25%

    T3:                  37%

   *T4:                  50%

    T5:                  62%

    T6:                  75%

    T7:                  87%

Here's a good website that describes the ACPI interface:
http://acpi.sourceforge.net/documentation/processor.html