Power Management Adventures on the Linux Desktop

If you are a normal, well-balanced person, you probably install a distro with a desktop environment, and when you want to change your power settings, you just search for the menu and do it. In my world, this is not how things are done—sorry.

I have already documented what I lost when I switched to a window manager and how I created a new status bar with dwmblocks . Now, the time has come to implement a power management feature.

Power!

For some time, I managed CPU frequency by setting the desired governor manually, such as performance or powersave.

echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

I’m not an animal—I didn’t type this command every time. Instead, I used a script that collects the available governors, which can be selected from a list using the beloved fzf command-line tool.

I didn’t have any problems per se, but another topic caught my attention.

Battery!

I found another tool called tlp, which optimizes laptop battery life automatically. It uses two profiles, ac and bat (I’ll let you figure out what they mean). It does cool stuff like changing CPU power when there is no work being done. You can also configure which governor should be used with each profile. And it optimizes power consumption of other devices as well. It’s neat!

It’s really easy to set up, and it has great documentation .

Profiles!

I became curious about how power management works in fully featured desktop environments like GNOME and KDE. It seemed to me that they use a tool called power-profiles-daemon. That certainly sounds like something that manages power profiles and is probably started with systemd. And yes, that is indeed what happens.

There was one downside: tlp and power-profiles-daemon are conflicting services because they manipulate similar parts of the system. From what I gathered from the interwebz: tlp is better for battery life, but for manual profile selection, power-profiles-daemon is the tool to use. So, for the time being, I will use the latter.

Implementing power management. (No more exclamation mark)

So, my desktop environment uses a set of tools that work together to make this happen.

• powerprofilesctl – the tool provided by power-profiles-daemon for managing power profiles.
• dmenu – a GUI fuzzy finder that provides a selectable list of profiles.
• dwmblocks – a status bar that shows the current profile.
• sxhkd – a tool with a hard-to-remember name that is responsible for key bindings.
• power – a shell script I wrote that handles interaction with powerprofilesctl and dmenu, and shows an icon representation of the profile.

Now, that’s decentralized as hell, so let’s visualize what happens when a key combination is pressed to change the profile.

So, while that may look like a lot, in practice I just added a new shell script, a new keybinding, and a new block for dwmblocks. Calling power set will open dmenu and set the profile; calling power get will echo an icon.

So, this is how you manage power profiles in two hours of work instead of just clicking a button. You’re welcome.