RFR: 8339573: Update CodeCacheSegmentSize and CodeEntryAlignment for ARM [v3]

[Boris Ulasevich]

On Mon, 7 Oct 2024 13:18:32 GMT, Evgeny Astigeevich <eastigeevich at openjdk.org> wrote:

>> Boris Ulasevich has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Relax CodeEntryAlignment. Default value is now 32B for Neoverse V1/V2, as recommended in the Optimization Guide.
>
> src/hotspot/cpu/aarch64/vm_version_aarch64.cpp line 263:
> 
>> 261:     }
>> 262:     if (FLAG_IS_DEFAULT(CodeEntryAlignment)) {
>> 263:       FLAG_SET_DEFAULT(CodeEntryAlignment, 32);
> 
> Why only for V1/V2? What about N1/N2?

There are reasons against the change for N1/N2
- Vladimir saw a regression when testing -XX:CodeEntryAlignment=16 on Ampere (Neoverse N1)
- with native codes experiment I found that code entry 64B is preferable on G2 (Neoverse N1)

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PR Review Comment: https://git.openjdk.org/jdk/pull/20864#discussion_r1790304217