PowerTOP is a Linux tool that finds the software component(s) that make your laptop use more power than necessary while it is idle. PowerTOP combines various sources of information from the kernel into one convenient screen so that you can see how well your system is doing, and which components are the biggest problem. With this tool you can find what software is using the most power on your system. Especially notebook users will benefit from reduced power consumption - there will be more time left on battery power.

Here is the complete rundown on how Powertop works.

C state information

C-states are operating modes of the CPU when it’s idle. The higher the C-state number, the less power is used by the CPU; however the longer it will take to get the CPU back to executing instructions.
C0 is special–in C0, the CPU is actually executing instructions. In all other C-states, the CPU is idle and not executing instructions.

To get decent power savings during idle, the CPU should be in C3 or C4 most of the time. In addition, the longer the average time in these C-states, the more power is saved. Ideally, your CPU spends at least 95% of its time in C4, for an average of 50 or more milliseconds.

Wakeups per second

The “Wakeups per second” line is another indicator for how well your laptop is doing in terms of getting power savings: the lower the number the better. When running a full GNOME desktop, 3 wakeups per second is achievable.

Power usage

When your laptop is running on battery, PowerTOP uses ACPI to collect information on how much power you are currently using. In addition, PowerTOP calculates an estimate for how many hours of battery you have left.

Note: If you’re not running on battery, or not running PowerTOP on a laptop, this information will not be available.

Top causes for wakeups

Now that we know the laptop is not doing well in terms of power usage, it’s time for the interesting part: what is causing the system to be more active than needed.

PowerTOP displays the top 10 activities on the computer during the sampling period.

Suggestions

The last section of the screen displays suggestions– PowerTOP has detected that the running kernel is configured suboptimally and suggests how to improve this.