[crac] RFR: 8374491: CPUFeatures: check performance regression of AVX_Fast_Unaligned_Load [v3]

[Jan Kratochvil]

On Mon, 5 Jan 2026 21:51:58 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

>> A regression by [JDK-8372863](https://bugs.openjdk.org/browse/JDK-8372863).
>> 
>> On AWS m1.small:
>> 
>> bin/java -XX:+ShowCPUFeatures --version
>> This machine's CPU features are: -XX:CPUFeatures=0x142000070bbdf,0x380
>> CPU features being used are: -XX:CPUFeatures=0x142000070bbdf,0x380
>> Re-exec of java with new environment variable: GLIBC_TUNABLES=:glibc.cpu.hwcaps=,-AVX_Fast_Unaligned_Load
>> This machine's CPU features are: -XX:CPUFeatures=0x142000070bbdf,0x380
>> CPU features being used are: -XX:CPUFeatures=0x142000070bbdf,0x380
>> openjdk 25-internal 2025-09-16
>> OpenJDK Runtime Environment (fastdebug build 25-internal-adhoc.azul.crac-git)
>> OpenJDK 64-Bit Server VM (fastdebug build 25-internal-adhoc.azul.crac-git, mixed mode, sharing)
>> 
>> That is a needless re-exec.
>
> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adjust the 'xem_xcr0_eax.bits.sse != 0 && xem_xcr0_eax.bits.ymm != 0' detection

filed: https://bugs.openjdk.org/browse/JDK-8374791 = [CRaC] [test] fileDescriptors/PatchModuleTest: guarantee(-1 != r) failed: can't stat fd

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PR Comment: https://git.openjdk.org/crac/pull/283#issuecomment-3723597813