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 Freq set up to use it.
Archlinux: https://wiki.archlinux.org/index.php/CPU_Frequency_Scaling
(if you have a good tutorial for your distro of choice, file a bug, I'll add it to the list)
You also need cpufreq-selector, which is usually in the gnome-applets package.
The best way to test you have these is to type in terminal:
which cpufreq-info
which cpufreq-selector
and check if they exist.
When the extension sets a governor, it does it one by one, calling cpufreq-selector for every cpu.
The problem here is that it will raise a popup asking for your password for each cpu. Typing the password for 4 CPUs can become quite annoying.
To solve this, I use (in archlinux):
Create and edit the file: /var/lib/polkit-1/localauthority/50-local.d/org.gnome.cpufreqselector.pkla
with:
[org.gnome.cpufreqselector]
Identity=unix-user:USER
Action=org.gnome.cpufreqselector
ResultAny=no
ResultInactive=no
ResultActive=yes
replacing USER with your username.
I'm open to any advice to make this easier/better.