Extending battery life on X200

Overview

I own the beautiful Lenovo X200 and run Ubuntu Intrepid on the machine. Its battery life is significantly lower than that under Windows and many users have reported that it runs hotter than under Windows.

With the changes below and a 9 cell battery I get over 9 hours on an idle system with backlight at the lowest level and wireless radios off. Before the changes I was only getting 5 hours.

The system also runs a lot cooler and I do not need tpfan (sw fan control for the ThinkPad available here), the built-in hw controller falls back to the lower speeds shortly after a CPU load subsides.

Details

The changes fall into 3 categories:

• Removing packages that create unnecessarily frequent wake up interrupts.
  • These interrupts wake up the CPU, preventing it from staying in its most energy efficient state.
  • I used Powertop from www.lesswatts.org for this task.
• Lowering the voltage supplied to the CPU.
  • Lowering CPU voltage does not impact performance since the clock frequency is unaffected
  • I used phc patches and phctools available at www.linux-phc.org for this task.
• Turning off radios you do not need
  • My X200 has 3 wireless radios: Wifi, Blutooth, Broadband wireless

Finding and removing high interrupt packages

Install PowerTOP from here.

Run PowerTOP as root (sudo powertop) and look for the packages that come up on top of the interrupt frequency list. These are the packages that wake up the CPU most frequently.

In my case the majority of the easily preventable interrupts were from 3 packages:

• i915, the intel graphics driver
• SCIM
• Gnome Power Manager

With the first one accounting for the bulk of the battery life improvement.

The %'s in PowerTOP give you an indication of what to focus on, no need to worry about a 1% problem (unless it is easy to prevent that it), it will not have much impact on your battery life.

Remember that over time these packages will improve and will not need to be removed.

Turning off DRI

Just insert: Option "NoDRI" to the "Device" section in /etc/X11/xorg.conf. This turns off all 3D, so no compiz or other fancy effect. Worth it for me because the impact on battery life is substantial.

Turning off SCIM

I had my system set to accept foreign characters. Going to System > Language Support > Disable support to enter complex characters does the trick.

Turning off Gnome Power Manager

You may decide you cannot live without it, but on my system I disabled Gnome Power Manager from the startup list: System > Sessions > Power Management daemon.

I replaced it with the Gnome Panel Battery Charge Monitor (Add to Panel...) which works well enough for me.

Reducing CPU voltage

Installing phc module patches

The phc module patches are available here, make sure you get the version that matches you kernel version. You can easily check by typing uname -r in a console.

You need not compile your own module, check the thread, users have posted already compiled versions of the acpi-cpufreg.ko module for most kernel versions.

Once you have the apci-cpufreq.ko module, back up the old module:

sudo cp /lib/modules/$(uname -r)/kernel/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.ko
/lib/modules/$(uname -r)/kernel/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.ko.bak

Then copy the new module to the right place:

sudo cp acpi-cpufreq.ko    /lib/modules/$(uname -r)/kernel/arch/x86/kernel/cpu/cpufreq

Restart your system and check that you now have voltage controls by typing: more /sys/devices/system/cpu/cpu0/cpufreq/phc_vids

You should see something like:

38 29 23 13 (your values may be different)

These are the voltage index values for the 4 frequencies available on your CPU. They are directly related to the actual voltages, phctools does the computation for you as explained below.

Intalling phctools

Download them here.

Unpack the package in a directory where you can conveniently access it. Use the install script (install.sh) to enable pctools to run without requiring a password.

Also download here the update which supports the Core2Duo CPU.

Unpack the archive and copy the file to"inc/libs" within the PHCTool directory (replace the old one).

Lastly made sure the module msr is loaded. PhcTool works without it, but having it loaded allows it to display the actual votage fed into your CPU.

sudo modprobe msr

You can make this module load automatically by adding it to the file /etc/modules

Also install the burnMMX application, it is designed to put a heavy load on your system and is necessary to make sure the voltages you choose will work under load:

sudo apt-get install burnMMX

Experimenting with lower voltages

This is the scary part: you will have to crash your system on purpose. I found it to be harmless, but be forewarned that some users have reported that it could damage your system.

DO NOT RUN THIS TEST WITH A CUSTOM PROGRAM TO CONTROL THE FAN, YOU COULD FRY YOUR SYSTEM. FIRST REVERT TO HW CONTROLLED FAN IF YOU MADE ANY CHANGES TO FAN CONTROL.

Check that you are using "ondemand" as the frequency scaling governor. This provided for the lowest power consumption according to Intel. An easy way to do this is to use Frequency Scaling Monitor Gnome panel applet.

Another way is to check:

/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

which returns the currently active governor. You can echo a new value as root, it takes effect immediately.

Start phctools:

phctools.sh

On the Info tab, you will see your CPU identified and the available frequencies for this CPU:

2267Mghz 2266Mhz 1600Mhz 800Mhz

On the Voltage tab you will see the VID and corresponding voltage for each frequency as well as the difference from the default values.

The phc patches prevent you from using a value higher than the highest defaults voltage or a value lower than the lowest default voltage even though phctools will let you enter higher and lower values. They will have no effect, so stay within the range defined by the highest and lowest VID value.

The default values are also reloaded each time you restart the system. Do NOT set phctools to "restore VID on load" at this time.

Now the fun begins...

1. Start burnMMX in a terminal window. WARNING this puts a lot of stress on yoru sys
2. Lower the first VID value, 25 should work to get started. Do this for both CPU's (tab on the left for CPU0 and CPU1
3. Save values
4. Use your system for a bit and see if it is stable
5. Lower the first VID value until your system crashes (or stop before if you do not dare)

For me 15 was the threshold. At this point reboot your system, restart phctools and set the first VID to the value that crashed + 2.

Restart for the other frequencies. I found that on my system I can safely set the VID for all 3 frequencies -other than the highest frequency- to the lowest value (the VID for 800Mhz). This may or may not be true for you.

Making the voltages stick

One you have found the lowest VID's that your system can safely run with, enter them on phctools Voltages for both CPU0 and CPU1, then go to settings and click "restore VID's on load".

All that is left is to make phctools restore your VID's each time you boot. Add the command

yourphcdirectory/phctools.sh background

to yours startup applications in System > Sessions. It will automatically start phctools, make it restore your VID's and quit.