Re: cpu temperature readings

[Masanobu SAITOH <msaitoh%execsw.org@localhost>]

Hi.

On 2023/06/28 14:24, Michael van Elst wrote:
> kre%munnari.OZ.AU@localhost (Robert Elz) writes:
> 
>> cpu0: "12th Gen Intel(R) Core(TM) i9-12900KS"
> 
> The chip apparently reports a Tjmax of 100 C (as for the non-selected chip)
> but actually has a real Tjmax of 115 C.

https://ark.intel.com/content/www/us/en/ark/products/225916/intel-core-i912900ks-processor-30m-cache-up-to-5-50-ghz.html

ark.intel.com often shows incorrect values. Looking at this page now,
it says Tjmax is 90 degrees.

Robert, could you show me the output of:

	dmesg -t | grep Tjmax

It seems that the MSR_TEMPERATURE_TARGET's value is not fixed
on newer chips. Please test the following diff:

	https://www.netbsd.org/~msaitoh/coretemp-20230628-0.dif

Thanks in advance.

> There are two caveats:
> 
> Our driver ignores Tjmax of > 110 C (and uses 100 C as default). If the
> chip would report the real value, we would ignore it.
> 
> Intel recommends that the BIOS fakes the value and configures the MSR ten
> degrees lower (so you see Tjmax of 90 C).
> 
> 
> The temperature sensor reading is relative to Tjmax.
> 
>                 /*
>                  * The temperature is computed by
>                  * subtracting the reading by Tj(max).
>                  */
>                 edata->value_cur = sc->sc_tjmax;
>                 edata->value_cur -= __SHIFTOUT(msr, MSR_THERM_STATUS_READOUT);
> 
> 
> So it could be 15C lower than reality (if the default of 100 instead
> of 115 is used) or even 25C lower if (if the Intel recommenendation
> is followed).
> 

-- 
-----------------------------------------------
                SAITOH Masanobu (msaitoh%execsw.org@localhost
                                 msaitoh%netbsd.org@localhost)