#1 2016-05-15 14:22:10

ghorvath

Member

Registered: 2015-10-01

Posts: 161

laptop-mode-tools for better battery consumption on laptops

Installation is with

sudo apt-get install laptop-mode-tools

Note, that laptop-mode-tools is probably not compatible with pm-utils or with TLP, there should always be only one power saving package.
The default settings should already give better battery times than without it. Some tweaking could be done, though.

I edited /etc/laptop-mode/laptop-mode.conf for having some of the advantages even on AC power. This is helpful if one has e.g. an ssd drive in the laptop, because then all ssd-related power savings (only writing data every 10 minutes to disk instead of 5 seconds, etc) will apply here, as well. 
So I have the line

ENABLE_LAPTOP_MODE_ON_AC=1

instead of the default 0 here. For battery power, I think the default is already 1.

Then I made further changes in files in /etc/laptop-mode/conf.d/
First and foremost, I tweaked my /etc/laptop-mode/conf.d/lcd-brightness.conf file so that when on battery, it would decrease the backlight of the screen. One thing to make sure is to have

CONTROL_BRIGHTNESS=1

otherwise this file is not going to be used by laptop-mode-tools. The other settings are specific to your laptop, e.g. on my Toshiba Portege R500 I have this:

BATT_BRIGHTNESS_COMMAND="echo 3"
LM_AC_BRIGHTNESS_COMMAND="echo 8"
NOLM_AC_BRIGHTNESS_COMMAND="echo 8"
BRIGHTNESS_OUTPUT="/sys/class/backlight/toshiba/brightness"

The other thing I changed is the /etc/laptop-mode/conf.d/dpms-standby.conf, I decided to turn it off so that it would not interfere with xfce4-power-manager. So just make sure to have

CONTROL_DPMS_STANDBY=0

instead of the default "auto" setting. And of course, make sure that you set up xfce4-power-manager properly.

Finally, for my other laptop (a Samsung Series 9 model) I modified the /etc/laptop-mode/conf.d/exec-commands.conf, because I have some specific tools for that laptop that helps to further enhance battery life:

BATT_EXEC_COMMAND_0="samsung_silent_mode on" # Enable power saving feature 0 here
LM_AC_EXEC_COMMAND_0="samsung_silent_mode off" # Enable power saving feature 0 here
NOLM_AC_EXEC_COMMAND_0="samsung_silent_mode off" # Disable power saving feature 0 here

BATT_EXEC_COMMAND_1="samsung_usb_charge off" # Enable power saving feature 1 here
LM_AC_EXEC_COMMAND_1="samsung_usb_charge on" # Enable power saving feature 1 here
NOLM_AC_EXEC_COMMAND_1="samsung_usb_charge on" # Disable power saving feature 1 here

BATT_EXEC_COMMAND_2="kbd_backlight 1" # Enable power saving feature 2 here
LM_AC_EXEC_COMMAND_2="kbd_backlight 4" # Enable power saving feature 2 here
NOLM_AC_EXEC_COMMAND_2="kbd_backlight 4" # Disable power saving feature 2 here

Here, samsung_silent_mode toggles the fan off, and at the same time it forces the CPU to its lowest power state. The samsung_usb_charge turns on/off the usb charging mode when the computer is in sleep. Finally, the kbd_backlight changes the power on the keyboard backlight.

Then after all the tweaking is done, enable and restart with

sudo systemctl enable laptop-mode.service
sudo systemctl restart laptop-mode.service

There are some caveats, though. For example, I noticed that the 4.x kernels do not observe properly if AC/battery status changed while sleep/powered off. Status change while the machine is on was never a problem. This was not an issue with the 3.16 stable kernel, but for my Samsung laptop I needed a newer kernel for keyboard backlights to work with the ambient light sensor. So with that laptop if I disconnect the laptop from AC, I always do it while powered on, so the kernel would remember that it is on battery. Then when I plug it in again, I always boot it up first, and then plug it in. This is a minor inconvenience I was willing to pay for the better keyboard backlight support. It also might be possible, that it is not entirely a kernel issue, but laptop-mode-tools issue, a newer version changed the way the power state is recognized, but it does not exists yet in backports, and I do not have the time to backport it myself.

With my Toshiba laptop I run the 3.16 kernel, and that seems to recognize the power state properly, even if changed during sleep/power off.