RFR: 8374926: EnableX86ECoreOpts was not enabled on some hybrid CPU [v3]

Yasumasa Suenaga ysuenaga at openjdk.org
Sun Jan 11 07:46:33 UTC 2026


> `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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into ecoreopt-hybrid
 - Merge remote-tracking branch 'origin/master' into ecoreopt-hybrid
 - Use supports_hybrid() to check for EnableX86ECoreOpts
 - Add comments for CPU models

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/29149/files
  - new: https://git.openjdk.org/jdk/pull/29149/files/8284b462..92e91552

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29149&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29149&range=01-02

  Stats: 18 lines in 2 files changed: 7 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/29149.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29149/head:pull/29149

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


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