Lenovo X200 running Coreboot drains 3-4W more power than with Vendor BIOS

[Daniel Kulesz]

      Hi,

I was wondering why my Lenovo X200 had such a short battery lifetime when running
Libreboot/Coreboot, so I did a few measurements using the following hardware
configuration:

X200 with P8700 CPU
8GB RAM
LED Display (yes, one of the rare ones)
OCZ Trion SSD (unused, just idling)
Wifi and WWAN removed
Battery removed
Ubuntu MATE 16.04 Live running from an USB thumb drive
No tweaking with powertop or such

I kept this configuration unchanged except for the BIOS and waited 5 minutes after
booting, so the system could settle. Then I measured power consumption both at full
brightness and at minimum brightness using a conventional power meter (EKM 365) which was
plugged between the AC adapter and the power socket in the wall.

I obtained the following numbers:

Vendor BIOS: 7,5W (lowest) to 10W (highest)
Libreboot 20150518 (using the precompiled binary binary): 13,3W (lowest) to 16,1W
(highest)
Latest Coreboot, config attached (80a3df260767a6d9ad34b61572d483579c21476c): 10,4W
(lowest) to 13,4W (highest)

While Libreboot performs much worse than Coreboot, Coreboot still eats around 3W extra
when compared with the vendor BIOS. In other words: Coreboot consumes around 30-40% more
juice than the vendor BIOS which is a very sad result for an ultraportable notebook.

Is this a known issue? Has someone else tried the same and obtained different numbers?

Cheers, Daniel

[Petrov, Andrey]

      Hi,

coreboot as such is not active once your system has booted. My guess is that with vendor
BIOS you are getting better working p-states and/or c-state residency than with coreboot.


I think lower max consumption with vendor bios can be attributed to the cpu really being
idle in your experiment. Could you try running stress -c 8 -m 8 on both stock bios and
coreboot bios and compare peak consumption? Also what happens if you boot on vendor bios
with idle=poll ? this will disable cstates, so if power consumption goes up, that  may be
the problem. You can also try with intel_pstate=disable on vendor bios and see if that
makes a dent on wattage.

Andrey

[Nico Huber]

      Hi Daniel,

first thing: We never got to the deepest processor sleep states (C3, C4)
when we originally ported coreboot for the GM45 chipset. But we didn't
see a difference in power consumption back then on the Roda/RK9.

On 01.05.2016 00:55, Daniel Kulesz via coreboot wrote:
  No tweaking with powertop or such
This might not
be a good idea: It's not always clear which power saving
options should be set by the firmware and which should be set by the os.
Anyway, I don't think it makes a big impact, but could you rerun your
measurements after `powertop --auto-tune`.

Nico

[Daniel Kulesz]

      Hi all,

thank you again for the suggestions!

First thing: VGABIOS. I was able to extract the blob (the hint in the wiki is a bit hidden
and the introduction of the section is a bit misleading btw) and re-ran the measurements
using the proprietary VGA BIOS:

Idle: 13,4W
Stress: 37,2W

So they values are exactly the same as with native graphics init. 

Second thing: Powertop. I did the suggested powertop --autotune experiments in idle and
obtained the following results:

vendor BIOS: 8,8W
Coreboot: 12,2W

So in both cases a decrease of around 1,2W.

But still something else drains these extra 3,5W. Not running in C3/C4 would explain that
difference maybe. How can I check that? I am now doing another attempt to include the
microcode updates, but I doubt this will make such a big difference.

Cheers, Daniel