Lenovo T410, enabling C3 state works perfect

[kuehro%posteo.de@localhost]

Hi,

on my Lenovo Thinkpad T410 (i5 M520) the fan was constantly spinning at 
3800 rpms
despite core temperatures below 40 degrees celsius. The fan was silent 
running under
OpenBSD which uses C3 power states. After enabling C3 with a NetBSD 
custom kernel
the fan control works perfect, with temperature around 65 degrees at 
full load and around
40 while idle, with fan spinning down. Suspend and resume works fine, I 
only have to switch
manually to X by using Strg+Alt+F5 after resume, but this was the case 
with the standard
kernel as well. I have used this kernel option for 3 month now and 
experienced no problems.
Just create a file /usr/src/sys/arch/amd64/conf/GENERICC3 like this:

include	"arch/amd64/conf/GENERIC"

options	ACPICPU_ENABLE_C3


and build the new GENERICC3 kernel as usual with kernel=GENERICC3

After installation run  vmstat -e  which should show thousands of C3 
MWAIT events like this:

acpicpu0 C3 (MWAIT)                          670194      304 misc


My best laptop experience with NetBSD ever. Everything works fine from 
builitin wlan (iwn)
to suspend and resume with a stable system even under days of full load.

Have fun,

Kai-Uwe


Relevant details from dmesg:

NetBSD 7.99.42 (GENERICC3) #0: Thu Nov  3 22:11:22 CET 2016
...
LENOVO 2537AT1 (ThinkPad T410)
...
acpicpu0: C1: FFH, lat   3 us, pow  1000 mW
acpicpu0: C2: FFH, lat 205 us, pow   500 mW
acpicpu0: C3: FFH, lat 245 us, pow   350 mW, bus master check