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Lenovo T410, enabling C3 state works perfect


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"


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,


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

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