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    SubjectRe: Linux 2.6.25 (coretemp reads high temperatures)
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    Hi all,

    I already answered this thread while ago. I can just confirm what Jean told.

    >>>> I confirm this.
    >>>> I *know* that temperatures reported now are wrong.
    >
    > And how do you know? The newly reported temperatures could be correct
    > and the previous ones were incorrect (that's actually the case.) The
    > thing is, the temperature is stored as a relative value in the CPU.
    > Relative to what, depends on the CPU model, can be 85°C or 100°C. Up to
    > kernel 2.6.24 we had a set of rules to find out, in 2.6.25 we have a
    > presumably better heuristic. So some people have seen their CPU
    > temperature climb by 15°C and others drop by 15°C, that's expected.

    Yes exactly. I decided to move to 0-100C scale, and move the limit too.
    Of course some users with too low jumped to better scale some like you seems to
    complain now.

    >>> i have watercooling, and well :P when i touch the "tube", its normal
    >>> room temperature, and believe me, i would notice if it was 45.. this is
    >>> with my cpu at idle - at full load on all 4 cores, temp2 says 35, and
    >>> ~60 on coretemp, and THIS i would surely be able to notice over room
    >>> temp :)
    >
    > The coretemp driver reports the CPU _core_ temperature. That's not
    > something you can touch, believe me (unless you are an electron.)
    >
    > Also note that the CPU temperature reported by the IT8718F may or may
    > not match the reality. To make sure, you'd need to know the type of
    > thermal diode expected by the IT8718F, the type of thermal diode in
    > your CPU, compute the correction factor if there is one. And you'd need
    > to know where the thermal diode is exactly. It is most certainly built
    > into the CPU, but some motherboard makers are doing weird things.
    >
    > 22°C seems very low to me, even for water-cooling. Note that
    > non-linearity of thermal diodes makes measurements inaccurate as they
    > get away from the expected operating point. I guess that thermal diodes
    > used in CPUs are calibrated for best results around the expected
    > temperature when using air-cooling, rather than water-cooling.
    >
    >>> any progress on this bug?
    >
    > I still need to be convinced that there is a bug here.

    It is not a bug, a max limit changed too, it is just matter how to scale it. The
    temperature is non-physical so comparing it to physical temperature does not
    make any sense. I'm sorry I did not invent this relative temp stuff - Complain
    @intel. They have some calibration of TjMAX for mobiles, but this bit does not
    work for desktops/servers. I tried really hard to get at LEAST some
    documentation so the driver looks like it looks. And not
    guessed/guessed/guessed/how it looked earlier.

    >
    >>>> The reason is that bios did report same temperatures as coretemp in 2.6.24,
    >>>> moreover some time ago I have run a cpu tool (don't remember its name) on windows

    It was most likely coretemp - I'm in contact with the guy. We share infos.

    >>>> temperature of both cores
    >>>> (I had to run this on windows - intel haven't released
    >>>> drivers for their QST for temperature monitoring from bios - very sad)
    >>>>
    >>>> And the driver did say in kernel log that TJMAX is 85C
    >
    > Which driver, which kernel? As I wrote above, the coretemp heuristic
    > changed in kernel 2.6.25, so the fact that a previous kernel was
    > reporting a different tjmax value is irrelevant. Unless you have
    > additional documentation from Intel, I would tend to believe that the
    > coretemp driver in 2.6.25 is correct. But feel free to report the exact
    > CPU model you have (with CPUID info) to Rudolf, if he gets enough
    > reports about a specific CPU model which most people believe gets the
    > wrong tjmax, he can fix the driver.

    Well again, I tried hard at Intel and I really could not get any info on some
    calibration bit. The temperature is non-physical on arbitrary scale. I changed
    that so for some people it jumped to 100C, for some it remained.

    >>>> Lets at least make a kernel option to override tjmax?
    >
    > That's a possibility for sure, but what we would really need is to
    > adjust the coretemp driver heuristics to always get it right - if
    > that's not already the case, that is. I'll let Rudolf decide anyway.

    Well again, Intel swears there is no way how to get the TjMAX for
    desktops/servers. It sucks but this is not my fault.

    Thanks,
    Rudolf






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