PowerTOP: 2x Display backlight

orschiro · 2014-04-02 18:17:34

Hi there,

On my Thinkpad X200T,PowerTOP shows me 2x power consumption for Display backlight.

See this screenshot: http://i.imgur.com/mP0H6hX.png

How should I interpret this?

Does my display use 4W in total or do I have indeed two different display backlights due to the tablet functionality of my thinkpad?

Or does PowerTOP interpret the display backlight twice because I have acpi_video0 and intel_backlight in /sys/class/backlight?

~ ls /sys/class/backlight 
lrwxrwxrwx 1 root root 0 2014-04-02 19:18:40.580222111 +0200 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
lrwxrwxrwx 1 root root 0 2014-04-02 19:41:48.878394230 +0200 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight

Is the double entry intended or should there be only one?

Thanks!

Last edited by orschiro (2014-04-02 18:18:37)

cafe · 2014-04-02 19:42:44

Hello orschiro,

I guess you could try to add the kernel parameter acpi_backlight=vendor to your bootloader. This will tell the kernel that you are using a custom backlight driver and that you don't want the default one to be loaded. In grub, this can be easily achieved by changing the fifth line of /etc/default/grub

GRUB_CMDLINE_LINUX="(..) acpi_backlight=vendor (...)"

And by running

# grub-mkconfig -o /boot/grub/grub.cfg

orschiro · 2014-04-03 05:23:53

Thanks cafe! However, it does not solve the issue.

Adding acpi_backlight=vendor, my brightness keys do no longer work. Furthermore, I still do have two entries in /sys/class/backlight.

Adding video.use_native_backlight=1 lets me control my brightness keys but still produces two entries.

lrwxrwxrwx 1 root root 0 2014-04-03 07:15:06.796659660 +0200 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
lrwxrwxrwx 1 root root 0 2014-04-03 07:15:06.796659660 +0200 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0

I guess there is no way around having these two entries.

Head_on_a_Stick · 2014-04-03 07:06:23

I have the same entries in my systemctl list; when I disable the acpi_video0 service the console brightness defaults to full while the X-system brightness remembers the last setting...
I could be wrong here but I think your system does use both settings --- try disabling the acpi service (with systemctl --- "systemd-backlight@acpi_video0.service") & see what happens.
Your backlight should account for a large portion of the power usage, changing the setting has a big affect on my battery.

orschiro · 2014-04-03 07:53:50

@Head_on_a_Stick

I think the acpi_video0.service cannot be disabled:

~ sudo systemctl status systemd-backlight@acpi_video0.service
● systemd-backlight@acpi_video0.service - Load/Save Screen Backlight Brightness of acpi_video0
   Loaded: loaded (/usr/lib/systemd/system/systemd-backlight@.service; static)
   Active: inactive (dead)
     Docs: man:systemd-backlight@.service(8)

Furthermore, I think it only stores the current brightness level for restoring on boot, correct?

Head_on_a_Stick · 2014-04-03 20:09:15

orschiro wrote:

Furthermore, I think it only stores the current brightness level for restoring on boot, correct?

Yes thats what the man page says

# systemctl mask systemd-backlight@backlight:acpi_video0.service

will disable the service and result in a 100% backlight setting with no adjustment possible...
I think both are needed
EDIT: right I've just tried

# systemctl mask systemd-backlight@backlight:intel_backlight.service

and now my backlight setting is remembered and adjustable --- maybe this .service isn't needed. My powertop doesn't show actual wattage dissipation for some reason so maybe you could try this & report back on any changes in power consumption?
However, the systemctl man page does say to use the "mask" option "with care"...

Last edited by Head_on_a_Stick (2014-04-03 20:15:47)

orschiro · 2014-04-04 13:41:51

@Head_on_a_Stick

I masked the intel_backlight.service but still PowerTOP displays backlight twice. I guess there is nothing we can do about it and probably it's a bug in PowerTOP.

cafe · 2014-04-04 14:03:34

Is it still listed in your /sys/class/backlight ?

orschiro · 2014-04-04 15:59:38

@cafe

Yes.

lrwxrwxrwx 1 root root 0 2014-04-04 17:55:54.053324936 +0200 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
lrwxrwxrwx 1 root root 0 2014-04-04 17:55:54.053324936 +0200 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0

lrwxrwxrwx 1 root root    9 2014-04-04 16:15:35.874536254 +0200 systemd-backlight@backlight:intel_backlight.service -> /dev/null

Does it work for you?

Head_on_a_Stick · 2014-04-04 20:57:58

@orschiro, may I ask how you get powerTOP to display watts dissipated? Mine just gives "usage" in milliseconds & microseconds per second...

orschiro · 2014-04-04 21:10:39

@Head_on_a_Stick

I just start `powertop` as root and then it displays the energy consumption in Watt. I thought this is the normal behaviour. Do you have a laptop or stationary system?

This is my Devices stats: http://i.imgur.com/wdcxAfD.png

And this Overview: http://i.imgur.com/5otlOKU.png

Head_on_a_Stick · 2014-04-04 21:16:09

I have a laptop. When I run "sudo powertop" it doesn't show the watts bit... V. strange

orschiro · 2014-04-05 06:22:01

Try this once:

powertop --calibrate

Head_on_a_Stick · 2014-04-05 09:54:31

Thanks @orschiro, but I've tried that a few times with no joy
Wierd thing is that I have Arch on my gf's laptop & powerTOP shows the wattage on her machine...

orschiro · 2014-04-05 10:05:38

@Head_on_a_Stick

How long did you run it it? I remember that initial calibration took a long time on my machine.

Head_on_a_Stick · 2014-04-05 12:24:27

Yeah it takes a long time, I ran it to completion a few times --- like I say, my girlfriend's laptop shows the wattage even without running the --calibrate option...
It doesn't really matter, I was just curious

sekret · 2014-04-05 12:57:18

The wattage is supposed to be shown no matter watt (lol), but it's more accurate with the calibration.

orschiro · 2014-04-06 00:11:57

Is there someone at all for whom PowerTOP only displays one backlight?

Last edited by orschiro (2014-04-06 00:12:11)

Head_on_a_Stick · 2014-04-06 14:20:49

orschiro wrote:

Is there someone at all for whom PowerTOP only displays one backlight?

I think it must be a bug in powerTOP because mine displays two backlights even after I've masked out the intel one via systemctl...

Arch Linux

#1 2014-04-02 18:17:34

PowerTOP: 2x Display backlight

#2 2014-04-02 19:42:44

Re: PowerTOP: 2x Display backlight

#3 2014-04-03 05:23:53

Re: PowerTOP: 2x Display backlight

#4 2014-04-03 07:06:23

Re: PowerTOP: 2x Display backlight

#5 2014-04-03 07:53:50

Re: PowerTOP: 2x Display backlight

#6 2014-04-03 20:09:15

Re: PowerTOP: 2x Display backlight

#7 2014-04-04 13:41:51

Re: PowerTOP: 2x Display backlight

#8 2014-04-04 14:03:34

Re: PowerTOP: 2x Display backlight

#9 2014-04-04 15:59:38

Re: PowerTOP: 2x Display backlight

#10 2014-04-04 20:57:58

Re: PowerTOP: 2x Display backlight

#11 2014-04-04 21:10:39

Re: PowerTOP: 2x Display backlight

#12 2014-04-04 21:16:09

Re: PowerTOP: 2x Display backlight

#13 2014-04-05 06:22:01

Re: PowerTOP: 2x Display backlight

#14 2014-04-05 09:54:31

Re: PowerTOP: 2x Display backlight

#15 2014-04-05 10:05:38

Re: PowerTOP: 2x Display backlight

#16 2014-04-05 12:24:27

Re: PowerTOP: 2x Display backlight

#17 2014-04-05 12:57:18

Re: PowerTOP: 2x Display backlight

#18 2014-04-06 00:11:57

Re: PowerTOP: 2x Display backlight

#19 2014-04-06 14:20:49

Re: PowerTOP: 2x Display backlight

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