laptop screen broken but display brightness still consuming power

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fabien85
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laptop screen broken but display brightness still consuming power

Post by fabien85 » Sat Jun 16, 2018 11:34 am

Hello,
I was given a MacBook Pro 2009 laptop where the screen does not work anymore. I suspect it's not the screen itself but the connection to the motherboard which is broken, since it's the hinge which got the shock and has visible damage.
Anyway I am setting this up as a home server, currently running a VPN server and with more plans for future.
And I want to decrease as much as possible the idle consumption, since the machine is going to be up near 100% of the year, and also to reduce the noise it makes (it's located on the desk where I work).

I have tried tlp (works well) and I'm now going more manually by running commands in /etc/rc.local to enable power saving settings. In both case I hit a plateau where I cant reduce the consumption below 17-18W (which is a lot compared to nowadays machines), with this strange result : here are the first few lines of powertop

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The battery reports a discharge rate of 17.4 W
The power consumed was 342 J
The estimated remaining time is 2 hours, 17 minutes

Summary: 283.7 wakeups/second,  0.0 GPU ops/seconds, 0.0 VFS ops/sec and 1.6% CPU use

Power est.              Usage       Events/s    Category       Description
  11.5 W      0.0%                      Device         Display backlight
  4.77 W      2.0 pkts/s                Device         Network interface: enp0s10 (forcedeth)
  1.31 W      0.0 pkts/s                Device         Network interface: wlp4s0 (wl)
  1.07 W      0.0 pkts/s                Device         nic:tun0
(lines below that add up to less than 1W of consumption)

So the display backlight consumes a lot of power, even though the screen doesnt work, the lid is closed, and I have set the brightness to zero (with echo 0 > /sys/class/backlight/gmux_backlight/brightness, and the brightness does appear with usage 0% in the "Device stats" tab of powertop). How can I cut this down ?
If I could cut down 10W of consumption, that would be fantastic.

More minor : the wireless wlp4s0 also consumes power, but I have no use to it since the laptop is connected by ethernet. I have set it's power management (in powertop the line "Runtime PM for PCI Device Broadcom Limited BCM4322 802.11a/b/g/n Wireless LAN Controller" is good), and shut it off with sudo ifconfig wlp4s0 down, but the powertop line remains the same around 1W. If anybody knows how to cut this down, that would also be a significant saving.

fabien85
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Re: laptop screen broken but display brightness still consuming power

Post by fabien85 » Sun Jun 24, 2018 4:22 am

Update:
I dismantled the laptop and took apart the screen. I put the thing back online and powertop shows I gained only ~0.5W.
I dont have the line for the wifi (the wifi antenna was in the hinge that I also removed), but still have that display backlight line

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11.5 W      0.0%                      Device         Display backlight
I dont know what else I can do.
At least the fans are now running at minimal speed most of the time.

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thx-1138
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Re: laptop screen broken but display brightness still consuming power

Post by thx-1138 » Sun Jun 24, 2018 7:27 am

...does vbetool change anything?

fabien85
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Re: laptop screen broken but display brightness still consuming power

Post by fabien85 » Sun Jun 24, 2018 10:30 am

Thanks for the answer.
I had tried vbetool, I just retried with your tutorial telling to add it to the sudoers file, it still fails :

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$ sudo visudo -f /etc/sudoers.d/vbetool
$ sudo vbetool dpms off
Real mode call failed
(where I wrote the correct content after the first command)
Anyway I'm not sure the command is supposed to work at all, since there is not even a screen now.
Maybe the line has to do with the graphic cards inside the laptop. I have set their setting to power saving in powertop though.

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BG405
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Re: laptop screen broken but display brightness still consuming power

Post by BG405 » Sun Jun 24, 2018 12:10 pm

Usage shows 0.0%, doesn't look like it's drawing power from what you've posted. Did you check the readings when the display was active, although not working? I'd expect more than 17W with a working display. Might be worth temporarily hooking the cables back up to test this.

If you've removed the display completely (like I have done with the Dell machine I'm using) and also the antenna wire(s), you may as well take the WiFi card out as well, if you haven't already done so. That might save a bit. Of course, you now have the added advantage of longer uptime in the event of a power cut. :D

I'll install & calibrate Powertop on a suitable machine later to see how much its diplay backlight draws & let you know for comparison. Can't do the calibration on this (Dell) or the other (ES1) as the former might not stay up long enough to calibrate & the latter has a completely dead battery.
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fabien85
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Re: laptop screen broken but display brightness still consuming power

Post by fabien85 » Sun Jun 24, 2018 1:26 pm

BG405 wrote:
Sun Jun 24, 2018 12:10 pm
Usage shows 0.0%, doesn't look like it's drawing power from what you've posted. Did you check the readings when the display was active, although not working? I'd expect more than 17W with a working display. Might be worth temporarily hooking the cables back up to test this.
the usage is 0% because I set the brightness to zero (using echo 0 > /sys/class/backlight/gmux_backlight/brightness as root). Following your thought, I have put the brightness to 100% and get this :

Code: Select all

Power est.              Usage       Events/s    Category       Description
  11.5 W    100.0%                      Device         Display backlight
and the power consumption is exactly the same as at 0% : ~17W.
So I guess I'm just overthinking it. Now that I removed the screen I cannot save more power on this side, and this line is just an artefact that doesnt mean.
(I was kinda hoping to be able to save more power, given my current laptop idles at ~5W. But I guess in the 10 year difference, CPU progressed a lot and consume way less power now)
If you've removed the display completely (like I have done with the Dell machine I'm using) and also the antenna wire(s), you may as well take the WiFi card out as well, if you haven't already done so. That might save a bit. Of course, you now have the added advantage of longer uptime in the event of a power cut.
I think I also removed the wifi card : if I'm not mistaken on this laptop both the antenna and the airport card are located in the hinge between the screen and the chassis. I will check this again.

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thx-1138
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Re: laptop screen broken but display brightness still consuming power

Post by thx-1138 » Sun Jun 24, 2018 1:38 pm

fabien, in regards to vbetool: i have no idea if it does something more drastic to DPMS compared to xset nowadays, hence the reason i asked...

Maybe playing around with acpi_osi= & acpi_backlight=vendor etc would give better results, considering it's a MacBook...

The only other thing that comes to mind in order to reduce power draw after removing / disabling devices & tlp would be to undervolt it.
That would certainly shave off a few Watts, but i don't know if it's even a possibility (never had a Mac myself)...

The 0% usage...let's just say i wouldn't really trust powertop 100%... :)
Googling for the fun of it the 0% usage reported on backlight, i stumbled upon this rather 'funny' case - using an external monitor:
https://superuser.com/questions/734817/ ... h-power-in

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BG405
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Re: laptop screen broken but display brightness still consuming power

Post by BG405 » Sun Jun 24, 2018 3:31 pm

I think 17.5W is rather economical, but if you're not using the graphics capabilities, i.e. have no monitor(s) connected, I wonder if it's possible to disable the GPU (assuming it's separate)? Sorry also don't know much about Mac computers.
Dell Inspiron 1525 - LM17.3 CE 64-------------------Acer D255E 2GB - Manjaro KDE, LM17.3 KDE 32
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fabien85
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Re: laptop screen broken but display brightness still consuming power

Post by fabien85 » Mon Jun 25, 2018 3:36 am

Thanks for the suggestions.
On macs you dont have access to a firmware interface / BIOS, which makes things a bit harder. I will look at the undervolting, I have never done that so need to do some research especially for a mac. For the GPU, I guess I need to disconnect them from the motherboard, that needs some research too.
I'm off for 10 days, will look at it when I come back, thanks !

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