Underclocking
2018-01-20
Program you're gonna need: cpupower. It's in the official repository.
More info: https://wiki.archlinux.org/index.php/CPU_frequency_scaling#cpupower
You can probably figure out the rest on your own...
Have a look at: /etc/default/cpupower
$ cpupower frequency-info
$ cpupower frequency-set -g powersave
$ cpupower frequency-set -u 3.1GHz
$ cpupower frequency-set -u 2.8GHz