Journal Linux

Laptop Power Saving with powertop on Fedora 22

The most important thing you want from a laptop is long battery life. Ever ounce of power you can get to work, read or simply just entertain on a long jaunt. Therefore, it’s always good to know what is consuming your power.

Intel’s powertop utility shows what’s drawing power when your system’s not plugged in. Use dnf to install powertop:

sudo dnf install powertop

powertop requires direct access to the hardware to measure power usage so you have to run it with root privileges:

sudo powertop

The powertop ouput will look similiar to the screenshot below. The measured power usage as well as system wakeups per second will most likely be different:

Screenshot of Powertop
Powertop 2.7 on Fedora 22

To switch between the multiple tabs use either the Tab or Shift+Tab keys. To quit the application, simply hit the Esc key.

The utility not only shows the power usage for various hardware and drivers but also displays the CPU stepping modes as well as systems wakeups per second. Processors are often so fast that they idle for the majority of the time.

The best way to maximize battery power is to minimize the number of wakeups per second. The best way to achieve that is to use powertops’ Tunable tab to optimise your laptop’s power savings. “Bad” usually indicates a setting that’s not saving power. In contrast, it might actually enhance the performance. “Good” indicates a setting is tuned to save power. Use the Enter key to turn any tunable on/off.

If you like to automatically turn all tunables on, the powertop package also includes a service that automatically sets all tunables to “Good” for optimal power saving. To start the service enter the following command:

sudo systemctl start powertop.service

To automatically start the service on boot timeĀ  enter the following command

sudo systemctl enable powertop.service

Probably the only caveat about this service and the tunables in general: Certain tunables may risk your data or result in some odd hardware behavior. For example, the “VM writeback timeout” settings affects how long the system waits before writing any changes of data to the actual disk. So you actually trade off data security for power savings. If the system loses all power for some reason, you might lose all the changes you made in the last 15 seconds, rather than the default 5. Nevertheless, for most laptop users this isn’t an issue since the system should warn you about low running battery.