Integrated: 8374926: EnableX86ECoreOpts was not enabled on some hybrid CPU

[Yasumasa Suenaga]

On Sat, 10 Jan 2026 03:34:22 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.

This pull request has now been integrated.

Changeset: 127bfc9b
Author:    Yasumasa Suenaga <ysuenaga at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/127bfc9b0dd122c78e702867a88e0847ec362e68
Stats:     4 lines in 1 file changed: 1 ins; 0 del; 3 mod

8374926: EnableX86ECoreOpts was not enabled on some hybrid CPU

Reviewed-by: vpaprotski, dholmes

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PR: https://git.openjdk.org/jdk/pull/29149