View the actual frequency and change CPU frequency governor from gnome shell.
There is a bit of work to make it work though.
You need CPU Frequency scaling set up to use it.
Debian: https://wiki.debian.org/HowTo/CpuFrequencyScaling
cpufrequtils is the tool we are using: apt-get install cpufrequtils
PLEASE PLEASE PLEASE READ THE DEBIAN LINUX WIKI PAGE CAREFULLY
I included the policy I use on Arch Linux (systemd init system) put it in /usr/share/polkit-1/actions/
https://github.com/Farsx
https://github.com/LeCoyote
https://github.com/victornoel
https://github.com/sonic414