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Power regression from Linux 5.2 to 5.3 under Debian on X390

Posted: Thu Feb 13, 2020 7:51 pm
by dcpurton
I'm running Debian Testing on a ThinkPad X390. The details of the system are:

** Model information
sys_vendor: LENOVO
product_name: 20Q0CTO1WW
product_version: ThinkPad X390
chassis_vendor: LENOVO
chassis_version: None
bios_vendor: LENOVO
bios_version: N2JET83W (1.61 )
board_vendor: LENOVO
board_name: 20Q0CTO1WW
board_version: SDK0J40700 WIN

Since upgrading to Linux 5.3 from 5.2 under Debian Testing, I am seeing a power usage regression. I run powertop --auto-tune on boot and all tunables are marked as good.

With Linux 5.2, powertop reported an idle battery discharge rate of between 3 and 4 W and CPU package C states seemed normal (majority of time spent in pc7).

However, with Linux 5.3, powertop reports an idle battery discharge rate of between 5 and 6 W. The CPU package C states are all reported as follows all of the time:

C2 (pc2)    0.0%
C3 (pc3)    0.0%
C6 (pc6)    0.0%
C7 (pc7)    0.0%
C8 (pc8)    0.0%
C9 (pc9)    0.0%
C10 (pc10)  0.0%

I noticed this with the first version of Linux 5.3 to be included into Testing.

I upgraded the UEFI BIOS from 1.55 to 1.61 to see if that would make any difference, but it didn't.

I did submit a bug report at ... bug=946922 but I'm getting sick of the reduced battery life and wondered if anyone here can suggest a workaround or option to pass to the kernel at boot.

I don't want to return to Linux 5.2 because I've found the track pad is better supported under 5.3 (under Debian at least).

I'd also like to avoid building my own kernel (just from a maintenance perspective and having to fiddle around with secure boot etc.)



Re: Power regression from Linux 5.2 to 5.3 under Debian on X390

Posted: Mon Mar 09, 2020 7:37 pm
by dcpurton
Looks like this issue has been fixed in Linux 5.5!

Everything is back to normal with great battery life.

I think it's this issue: