linux-kernel - Re: Linux 2.6.25

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Date:	Fri, 18 Apr 2008 22:50:36 +0200
From:	Rudolf Marek <r.marek@...embler.cz>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	Bart Van Assche <bart.vanassche@...il.com>,
	Matthew <jackdachef@...il.com>, torvalds@...ux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Gene Heskett <gene.heskett@...il.com>,
	LM Sensors <lm-sensors@...sensors.org>
Subject: Re: Linux 2.6.25

Hi all,

I will keep the rest of the mail intact for the lm-sensors list. The temperature 
is stored in hardware relative to maximum temperature. Mobile processors have 
some undocumented bits that calibrate the temperature to 85 or 100C. Intel 
claims that this does not work for desktops, so I changed the driver [1] and 
scale for desktop CPUs is from 0 to 100.

In your case, the MAX temperature is changed from 85 to 100 for desktops But the 
relative change is same, in your case -40C below the max [2]. You should now see 
instead of 40 around 60. Because it was 85 - 40 and now it is 100 - 40. Second 
problem is that the scale is not linear so it works more fine close to the MAX.

I think it is what happened. If you change the driver, so it will take 85C 
instead of 100C everything should go back to "normal". I'm sorry I did not 
invent relative only temp measurements, therefore I would recommend to watch how 
much is left to max temperature.

Hope it explains it,

Thanks,
Rudolf

[1] 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=118a88718886a6cb7fb2cf7fb77ef2eea30c73a1
[2]
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/hwmon/coretemp;hb=HEAD


Jiri Slaby napsal(a):
> On 04/18/2008 09:18 PM, Bart Van Assche wrote:
>> On Fri, Apr 18, 2008 at 5:37 PM, Matthew <jackdachef@...il.com> wrote:
>>>  I've another "regression" to report for 2.6.25:
>>>
>>>  it's concerning much higher temperatures being read out by the
>>>  "coretemp" kernel-module in comparison to 2.6.24* series
>>>
>>>  e.g. where temperatures were around 40-47°C they are now constantly
>>>  jumping around 55-70°C (even in idle !)
>>
>> The coretemp kernel module reports 25°C on my PC when idle, and 34°C
>> after having performed some computations (lmbench2). This looks
>> normal. This test has been performed with a vanilla 2.6.25 kernel and
>> a Core 2 Duo E6750 CPU (Asus motherboard). The 2.6.22 and 2.6.24
>> kernels report an incorrect temperature on the same system however
>> (10°C). So there is either an issue with the patches that have been
>> applied to your kernel or the behavior of the coretemp module for the
>> 6600 and E6750 CPU's is different. Can you repeat the test with a
>> vanilla 2.6.25 kernel ?
>>
>> (Added Rudolf Marek in CC, the coretemp author.)
> 
> I see a change on my rrd graphs on Mar 5th 11:30 AM (from 25 to 40 
> average centigrades). This is when I booted 2.6.25-rc3-mm1 instead of 
> 2.6.25-rc2-mm1, according to logs. [I have no idea whether the values 
> were correct before or are correct now.]
> 
> I might bisect it, if needed.
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