Changing CPU frequencies can be interesting to measure certain energy efficiency aspects. To manually change the CPU frequency in Ubuntu, first install cpufrequtils to get the additional commands:
sudo apt-get install cpufrequtils
See the available CPU frequencies, the current frequency and governor per core.
$ cpufreq-info
cpufrequtils 007: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:
driver: powernow-k8
...
available frequency steps: 2.60 GHz, 2.30 GHz, 1.80 GHz, 1.30 GHz, 800 MHz
available cpufreq governors: conservative, ondemand, userspace, powersave, performance
current policy: frequency should be within 800 MHz and 2.60 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 800 MHz.
cpufreq stats: 2.60 GHz:1.77%, 2.30 GHz:0.33%, 1.80 GHz:0.20%, 1.30 GHz:0.34%, 800 MHz:97.35% (63965465)
To be able to change the frequency, we have to change to the userspace frequency.
sudo cpufreq-set -g userspace
Finally, we can switch the actual frequency to one of the available values with:
sudo cpufreq-set -f 2.6GHz
This happend per-core on the server I tested the procedure on. You can select e.g. CPU 2 using the -c2 option. Also, don’t forget to change back to the default ondemand governor once you’re done – you wanna stay green 😉
References:
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