Why is the backlight consuming so much power?

andrushkin · 2014-11-08 19:36:18

Powertop is showing my backlight running at 10+ Watts, is there any way to fix this problem? An LCD does not usually consume so much energy, especially at lowest brightness.

Thanks

>inxi -Fs
System:    Host: pulse Kernel: 3.14.23-1-lts-ck x86_64 (64 bit)
           Desktop: Gnome 3.14.1.5 Distro: Arch Linux
Machine:   Mobo: ASUSTeK model: N53SN v: 1.0
           Bios: American Megatrends v: N53SN.208 date: 08/10/2011
CPU:       Quad core Intel Core i7-2670QM (-HT-MCP-) cache: 6144 KB 
           clock speeds: max: 2201 MHz 1: 900 MHz 2: 2201 MHz 3: 800 MHz
           4: 1600 MHz 5: 800 MHz 6: 800 MHz 7: 800 MHz 8: 800 MHz
Graphics:  Card-1: Intel 2nd Generation Core Processor Family Integrated Graphics Controller
           Card-2: NVIDIA GF108M [GeForce GT 550M]
           Display Server: N/A driver: intel Resolution: 80x25
Audio:     Card Intel 6 Series/C200 Series Family High Definition Audio Controller
           driver: snd_hda_intel
           Sound: Advanced Linux Sound Architecture v: k3.14.23-1-lts-ck
Network:   Card-1: Intel Centrino Wireless-N 1000 [Condor Peak]
           driver: iwlwifi
           IF: wlp3s0 state: up mac: 74:e5:0b:48:c0:ca
           Card-2: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
           IF: N/A state: N/A speed: N/A duplex: N/A mac: N/A
Drives:    HDD Total Size: 1006.2GB (5.8% used)
           ID-1: /dev/sda model: SanDisk_SDSSDHP2 size: 256.1GB
           ID-2: /dev/sdb model: ST9750420AS size: 750.2GB
Partition: ID-1: / size: 14G used: 5.7G (44%) fs: ext4 dev: /dev/sda5
           ID-2: /home size: 37G used: 1001M (3%) fs: ext4 dev: /dev/sda6
           ID-3: swap-1 size: 10.74GB used: 0.00GB (0%) fs: swap dev: /dev/sda4
Sensors:   System Temperatures: cpu: 47.0C mobo: N/A
           Fan Speeds (in rpm): cpu: N/A
Info:      Processes: 163 Uptime: 11 min Memory: 797.4/7881.3MB Init: systemd
           Client: Shell (bash) inxi: 2.2.16

I have the discrete GPU disabled and am running TLP.

Last edited by andrushkin (2014-11-08 19:59:20)

jasonwryan · 2014-11-08 19:41:18

Kernel? Hardware? Any relevant detail?

Please see: How To Ask Questions The Smart Way...

andrushkin · 2014-11-08 19:58:19

Updated original post with info. I have been trying to solve this problem for a LONG time, I've searched the internet extensively for any material that could help me with the matter, so far everything I have tried has not helped at all.

Last edited by andrushkin (2014-11-08 20:48:55)

clfarron4 · 2014-11-08 21:24:03

Is that using that kernel as I provide it in my repositories or one that you compile yourself?

Does it occur with the linux-lts package?

How are you managing the Integrated and Discrete cards?

Last edited by clfarron4 (2014-11-08 21:24:18)

andrushkin · 2014-11-08 21:49:39

clfarron4 wrote:

Is that using that kernel as I provide it in my repositories or one that you compile yourself?
Does it occur with the linux-lts package?
How are you managing the Integrated and Discrete cards?

Yes, the problem occurs under the lts kernel and the vanilla kernel as well. I compiled the kernel myself. As for the discrete nvidia card, I have disabled it using bumblebee and bbswitch with the systemd service bumblebeed.

Really? Nobody knows how to handle this?

Last edited by andrushkin (2014-11-09 17:54:28)

andrushkin · 2014-11-09 18:16:50

I'd also like to note that this does not occur in other distros (Ubuntu, linux mint)

ewaller · 2014-11-09 19:25:38

I am not surprised by 10W for a backlight. On a large display, 20 to 40 Watts is not uncommon Ignoring everything else that draws power from the battery, a 10,000 mWh battery could power the backlight for 10 hours, or so. The boils down to around 100mW/square inch for a 100 square inch display. In general, I find the backlight takes the lion's share of the power. Assume everything else takes as much power as the backlight, I am guessing you should be able to run for about five hours.

Any chance your instrumentation is lying to you on the other distributions?

kokoko3k · 2014-11-09 19:46:24

andrushkin wrote:

Powertop is showing my backlight running at 10+ Watts, is there any way to fix this problem?

As far as i know, powertop does estimations based on a calibration stage.
Maybe something went wrong, and now it is reporting bad values.
What if you completely power off the display?
Start powertop, wait 30 secs, then issue:

xset dpms force off

wait 30 seconds and check powertop again.
If it still says that the backlight is draining power, then there is something wrong with powertop.

Last edited by kokoko3k (2014-11-09 19:48:02)

firecat53 · 2014-11-09 20:07:10

For what it's worth, I've noticed that powertop still says the backlight on my laptop is using power when I've got an external VGA monitor attached and the laptop LCD is completely off.

Scott

andrushkin · 2014-11-10 01:19:13

ewaller wrote:

Any chance your instrumentation is lying to you on the other distributions?

I don't think so, I have managed to idle Ubuntu for ~8 hours, whereas idleing Arch results in hardly ~4.5 hours.

kokoko3k wrote:

Start powertop, wait 30 secs, then issue:
xset dpms force off
wait 30 seconds and check powertop again.
If it still says that the backlight is draining power, then there is something wrong with powertop.

Since this is the only screen I am using, I ran

xset dpms force off; 
sleep 30;
xset dpms force on;

Shortly after the display resumes Display Backlight is at 0% usage and 0W, once powertop refreshes it is back at 10 W. ;/

Last edited by andrushkin (2014-11-10 01:20:25)

andrushkin · 2014-11-16 20:46:26

Bump....?

kokoko3k · 2014-11-17 15:20:02

Well, giving that your run time under ubuntu was greater than arch, there is still a chance that powertop is giving you wrong stats and the culprit is some other thing.
Could you please do what i said you before and check that the system power consumption goes down by 10Watts by simply switch off the display?

Pse · 2014-11-17 23:56:35

Have you tried switching between Intel P-State and ondemand to see if it makes any difference? AFAIK, people have had mixed results with Intel P-State.

andrushkin · 2014-11-25 14:48:37

kokoko3k wrote:

Well, giving that your run time under ubuntu was greater than arch, there is still a chance that powertop is giving you wrong stats and the culprit is some other thing.
Could you please do what i said you before and check that the system power consumption goes down by 10Watts by simply switch off the display?

Thanks, I've checked using both powertop and powerstat, during the time that the backlight is off power consumption is ~1W

kokoko3k · 2014-11-25 16:35:21

Then you have NOT to trust powertop at all, something is very wrong with it.
1W is a power consumption you'd expect from a raspberry pi idling, not from a cpu like yours that had a tdp of 45W max...

Arch Linux

#1 2014-11-08 19:36:18

Why is the backlight consuming so much power?

#2 2014-11-08 19:41:18

Re: Why is the backlight consuming so much power?

#3 2014-11-08 19:58:19

Re: Why is the backlight consuming so much power?

#4 2014-11-08 21:24:03

Re: Why is the backlight consuming so much power?

#5 2014-11-08 21:49:39

Re: Why is the backlight consuming so much power?

#6 2014-11-09 18:16:50

Re: Why is the backlight consuming so much power?

#7 2014-11-09 19:25:38

Re: Why is the backlight consuming so much power?

#8 2014-11-09 19:46:24

Re: Why is the backlight consuming so much power?

#9 2014-11-09 20:07:10

Re: Why is the backlight consuming so much power?

#10 2014-11-10 01:19:13

Re: Why is the backlight consuming so much power?

#11 2014-11-16 20:46:26

Re: Why is the backlight consuming so much power?

#12 2014-11-17 15:20:02

Re: Why is the backlight consuming so much power?

#13 2014-11-17 23:56:35

Re: Why is the backlight consuming so much power?

#14 2014-11-25 14:48:37

Re: Why is the backlight consuming so much power?

#15 2014-11-25 16:35:21

Re: Why is the backlight consuming so much power?

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