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Saving power is one of the major concerns of the modern world. You see cities observing Earth Hours, studies showing how computers consume excess power when kept running and so on. Even if you would view it from your personal perspective, saving power can make your laptop batteries last longer and provide longer battery backup.

If you use Linux, there is an excellent tool that gives you loads of information about your computer’s power consumption as well as the software that is causing your battery to drain. Its called PowerTop.

PowerTop was originally developed by Intel and it lets you measure and explain your computer’s power consumption.


As always, check your distribution’s package manager for a package named ‘powertop’. If you cannot find it listed there, head over to the PowerTop website and download the tar ball which you can compile and run.

Be sure to run PowerTop with root privileges. It takes about 5 seconds to collect data and it then presents its findings for your consideration. The output can be overwhelming for the uninitiated so lets go through it briefly:


The first part represents the C-States. C-States are the operating modes of the CPU and are usually represented in the form of “Cx” where x is a number. The higher this number, the less power will be used by the CPU in that state. So in this first part you will see the amount of time the CPU has been in each of these states.

P-states shows the frequency the processor is currently running on. In its idle state it will be running at the lowest supported frequency.

The next part represents “Wakeups per second” and means how many times the CPU has been woken from an idle state. Of course, the smaller the value of this number, the better your computer is performing in terms of power consumption.

The next part shows the battery information if you are using a laptop or no information if you are on a desktop.

Then it lists the top reasons for wakeups. This is the most interesting part as it shows which of the software is causing the CPU to wake from an idle state and thus consume power. The PowerTop website also offers patches for many software which are reported to be reasons for unnecessary power consumption.

Lastly the program lists some suggestions you can follow to decrease the power consumption of your computer.

So once you have the output and you’ve read it, what should you then do about it? Well a couple of straight forward steps that you can follow:

  • Look for the top causes for wakeups and see if you can disable some of them. It may be bluetooth or wi-fi when you don’t need them or something else. If you don’t need them then disable them.
  • Check out the most common known reasons for wakeup and how to tackle them.
  • Look for software patches on the PowerTop website and apply them (make sure to check versions, as some of them may be outdated). They tend to take care of bugs (or provide workarounds) to code that causes the CPU to wake up constantly.
  • Follow the suggestions PowerTop has to offer. You might want to Google the message it gives you if it seems to be a bit too geeky for you. Chances are you will find a step by step guide to achieve the same.
  • Read Saikat’s article on conserving battery power 20 Ways To Increase Laptop's Battery Life 20 Ways To Increase Laptop's Battery Life Read More . Although not directly related to the analysis method which we just followed, he provides some pretty nifty tips in general that you must check out.

PowerTop not only monitors the power consumption but also provides you with detailed information on how you can minimize the consumption. An indispensable tool for laptop users especially. After tweaking for some days I really got the battery power back up and I am still not convinced I have the perfect setup (working on it).

How do you minimize your laptop’s power consumption? Turning off Wi-Fi or turning down the screen brightness or something else? We would really like to hear about them in the comments.

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  1. mchlbk
    April 8, 2009 at 7:52 am

    Been looking for a way to reduce my laptop's power consumption when running *buntu.

    When running Vista I undervolt the CPU using Rightmark CPU Clock Utility. That way the max core temp. is 60-65 degrees Celcius (140-149F). Without Rightmark max temperature is close to 100C (212F).

    Ideas on how to undervolt in linux?

  2. Mackenzie
    April 7, 2009 at 10:43 pm

    I blacklist the Bluetooth module for both security and battery life.

    When I'm not using wireless (ex: I'm on a train/plane), I unload my wireless module as well. My boyfriend unloads his ethernet module, but I usually forget to do this.

    For me, those would be:
    # modprobe -r btusb iwlagn sky2

    If it has to be quiet and I don't have headphones, well, no point in having sound drivers, is there?
    # alsa force-unload
    Though warning, this will kill all running sound apps (including any volume mixer applets you have on your panel).

    You can load modules again when you're done with:
    # modprobe
    Giving it a list of modules where it says .

    Warning: If you use the K option (disable polling CD ROM drive), you will need to manually mount your CDs with:
    sudo mount -t iso9660 /dev/cdrom /media/cdrom
    or something close to that (check your mountpoint and device nodes).

    Note that "#" means at a root prompt. Ubuntu users, that means "use sudo".

    If you want to see what modules are in use, the "lsmod" command will tell you. Here are common things you can look for:
    Intel: lsmod | grep "iwl\|ipw"
    Atheros: lsmod | grep "ath\|madwifi"
    Prism or Orinoco chipsets: lsmod | grep "orinoco\|hostap\|wlan"
    Broadcom: lsmod | grep "^b*43*"
    Realtek or Ralink chipsets: lsmod | grep "^rt"
    lsmod | grep "^snd"
    sky2 is one of the most common for laptops

  3. Vadim P.
    April 7, 2009 at 7:15 pm

    It is useful when you're on batteries and want to save more.