RFR: 8365633: Incorrect info is reported on hybrid CPU [v2]

[Vladimir Kozlov]

On Fri, 22 Aug 2025 00:33:10 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> @YaSuenag  Is it possible to find from CPUID or OS calls the information about hybrid CPU configuration?
>> 
>> "( 2 P cores, 8 E cores, 2 LP cores)" in you case.  I would prefer if for hybrid CPU we print that info instead of "(7 cores per cpu, 2 threads per core) ".
>> 
>> It is important information when we debug issue on such CPUs.
>
>> Is it possible to find from CPUID or OS calls the information about hybrid CPU configuration?
> 
> I hope so too, but it is difficult as @dholmes-ora said unfortunately.
> 
> We can use `1Ah` leaf of `CPUID` to identify whether P core or not like [this code](https://github.com/YaSuenag/garakuta/blob/ebe4c8da6ed890f6144c1c32ff02b5ed3200df14/check-hybrid-cores/hy-core-check.c#L60-L95). However we would face following problem:
> 
> 1. Leaf `1Ah` returns the information for the logical processor which was issued - we need to issue `CPUID` on all of logical processors with processor affinity.
> 2. We can identify "Intel Core" (P core) or not ("Intel Atom") via leaf `1Ah`, however we might not distinguish whether E core or LP core.
>     * In Core Ultra 5 225U, both E core and LP core is Crestmont, thus they have same native model ID.
> 
> OS (Windows and Linux at least) cannot expose information about details of CPU cores AFAICS, thus it is difficult to show processor details to the user on `VM.info` and hs_err log.

@YaSuenag Thank you for additional information. Yes, I agree with David and you.

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PR Comment: https://git.openjdk.org/jdk/pull/26808#issuecomment-3212576807