Saturday, February 12, 2011

lm_sensors and Tjunction-max

Recently, the temperature values being reported by lm_sensors on my linux-lap were becoming a point of concern. The fan and heatsink assembly had just been cleaned a few days earlier but still lm_sensors reported my CPU was at ~70C while idling! Even considering the fact that I live in a hot part of the world, the values were too high for this time of the year and for an idling CPU. Checking the logs and a bit of web research revealed the culprit:

 └─>>$] dmesg | grep Tj
coretemp coretemp.0: TjMax is assumed as 100 C!
coretemp coretemp.1: TjMax is assumed as 100 C!

The Intel datasheet for a T5750 processor reports the designed Tj-max as 85C but gets detected as 100C, so lm_sensors was reporting the values with a +15C offset.

The bug seems to be in a recent git commit as explained in this thread:
Tjunction explained:

FIX: After discussing the issue with the devs on IRC, a small fix was suggested. Worked for me.

edit '/etc/sensors3.conf' and add the lines 
chip "coretemp-*"
    compute temp1 @-15,@+15
    compute temp2 @-15,@+15

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