RFR: 8374926: EnableX86ECoreOpts was not enabled on some hybrid CPU [v5]

[Yasumasa Suenaga]

On Sat, 24 Jan 2026 02:38:22 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> `EnableX86ECoreOpts` has been introduced in [JDK-8319429](https://bugs.openjdk.org/browse/JDK-8319429), however model numbers which should be enabled are hard-coded, so the flag would not be enabled by default on some models like Arrow Lake.
>> 
>> I ran a [benchmark](https://github.com/YaSuenag/garakuta/tree/master/randminmax) to check for effectiveness of `-XX:+EnableX86ECoreOpts` with JDK 25.0.1 on Windows 11 25H2, I saw performance improvement a bit on Intel Core 5 Ultra 225U as following:
>> 
>> Disabled (default)
>> 
>> Benchmark Mode Cnt Score Error Units
>> RandMinVal.getMax thrpt 3 9707774.405 ± 27082629.015 ops/s
>> RandMinVal.getMin thrpt 3 7510319.839 ± 10923547.382 ops/s
>> 
>> 
>> Enabled
>> 
>> Benchmark Mode Cnt Score Error Units
>> RandMinVal.getMax thrpt 3 10127809.127 ± 45404142.338 ops/s
>> RandMinVal.getMin thrpt 3 8467677.056 ± 1211998.200 ops/s
>> 
>> 
>> So I think it is better to enable this flag by default on all of hybrid CPUs.
>> 
>> 
>> To check what processor would be enabled E-core optimization, I made a [commit](https://github.com/openjdk/jdk/commit/f363ea1436b8100021fdac87b48ec43bcf6820af) to add comments for CPU models at first. I couldn't find out all of models (some models has not listed in SDM vol.4 so far), but most of models (excepts Sierra Forest) could be treated as hybrid CPU. Fortunately HotSpot identify hybrid flag from `CPUID`, so we can leverage it for this purpose.
>
> Yasumasa Suenaga has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Add condition for CWF
>  - Revert "Check E-Core with Leaf 1Ah"
>    
>    This reverts commit d77b43937911b33bf39175e45e3d9d97aa949617.

Thanks a lot for your help!

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PR Comment: https://git.openjdk.org/jdk/pull/29149#issuecomment-3810652432