How to make use of Dynamic Frequency Scaling
Contents
general
Linux supports Dynamic Frequency Scaling for ThinkPads with mobile Pentium III, Pentium 4 and Pentium M processors.
configuring the kernel
2.4 kernels
Todo...
2.6 kernels
You need to enable the cpu frequency scaling for your kernel (usually your distros kernel will have this enabled):
CONFIG_CPU_FREQ=y
You need to load enable governors, if not already done in your distros default kernel:
CONFIG_CPU_FREQ_GOV_PERFORMANCE=y CONFIG_CPU_FREQ_GOV_POWERSAVE=y CONFIG_CPU_FREQ_GOV_USERSPACE=y
Since 2.6.10 there is the ondemand governor that does cpu frequency scaling in kernel so you dont need userspace programs like powernowd etc. It can be enabled with:
CONFIG_CPU_FREQ_GOV_ONDEMAND=y
- If you have a Coppermine-piix-smi based Thinkpads like from the A2x, X2x and T2x series you need to enable the speedstep-ich driver in the kernel and load it if it's built as module. You might want to look at this page.
- If you have a p4-class celeron based Thinkpad like the R40e you might want to look at this page
using the sys interface
The files in /sys/devices/system/cpu/cpu0/cpufreq/ provide information and a means of controlling the frequency scaling subsystem. Seed values are given in Khz. You need to be root to access the /sys filesystem.
Your max speed is at /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq.
# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
- 700000
Your min speed is at /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq.
# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq
- 500000
You can write to /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed to change the current speed.
# echo 700000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
# cat /proc/cpuinfo
- cpu MHz : 697.252
# echo 900000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
# cat /proc/cpuinfo
- cpu MHz : 976.152
configuring SpeedStep daemons
Don't forget to enable the userspace governor to have a userspace daemon do the frequency scaling. If it is built as module, load it as cpufreq-userspace. Note that since 2.6.10, there is also the ondemand governor in the kernel, which replaces any userspace daemon for cpu scaling and works very well.
There are plenty of userspace frequency scaling daemons available: