Switching on PowerNow in Linux

June 18, 2006 at 9:49 pm Leave a comment

Ubuntu 6.06 managed to work right away on the Presario 906us. When I run dmesg, I get the following:

[17179574.836000] ACPI: CPU0 (power states: C1[C1] C2[C2])
[17179613.464000] powernow: PowerNOW! Technology present. Can scale: frequency and voltage.
[17179613.492000] powernow: SGTC: 13333
[17179613.492000] powernow: Minimum speed 530 MHz. Maximum speed 1325 MHz.

To check which setting the cpu freq governor is set to, you can do a:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor  

The default is usually userspace. The settings for powernow are:

  • powersave – minmal cpu speed
  • conservative – change cpu speed according to load, but err on the conservative side to save power. Good for laptop.
  • ondemand – change cpu speed according to load, but err on the performance side. Good for desktop.
  • performance – highest cpu speed possible.
  • userspace – controlled by the user.

 I decided to use conservative setting. I added the following to the /etc/rc.local file:

# Set CPU Scaling to use power conservatively since this is a laptop
echo conservative > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

The line will set the cpu freq to convervative on startup. 

Entry filed under: linux.

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