How to get SpeedStep working on P4-class-Celeron based ThinkPads

Introduction

If you have an P4-class Celeron based Thinkpad (like the R40e in my case) you can use the p4-Clockmod scaling option from 2.6 kernels to set cpu speed. Use any userspace daemon like powernowd or cpufreqd to get dynamic speedstepping to work.

Kernel config

CONFIG_CPU_FREQ=y
CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE=y
CONFIG_CPU_FREQ_TABLE=y
CONFIG_X86_P4_CLOCKMOD=y (for R40e, p4-class celeron, other tp's might need something different here)

make sure to have the sys interface built within your kernel

CONFIG_SYSFS=y

using the sysfs interface

use the sys-interface to discover and set available frequencies

make sure to have sysfs mounted: add

none            /sys            sysfs           defaults                0      0

to your /etc/fstab (if not already there)

get available freqencies:

laptop:~# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
275000 550000 825000 1100000 1375000 1650000 1925000 2200000

set frequency:

laptop:~# echo 825000 >/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed

use powernowd (easier) or cpufreq (more settings) to have cpuspeed dynamically managed

Powernowd

for powernowd use the sys interface to set the min and max speed:

laptop:~# echo 825000 >/sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
laptop:~# echo 2200000 >/sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
laptop:~# /etc/init.d/powernowd start

on my R40e frequencies below 825000 make x almost unusable (mouse jumps around, until cpuspeed rises)

cpufreqd

TODO