RFR: 8343978: Update the default value of CodeEntryAlignment for Ampere-1A and 1B

[Boris Ulasevich]

On Fri, 15 Nov 2024 07:01:23 GMT, Liming Liu <lliu at openjdk.org> wrote:

> This PR updates the default value of CodeEntryAlignment for Ampere-1A and 1B from 64 to 32. The microbenchmark CodeCacheStress shows that frontend stall becomes ~21% smaller by the change, and IPC increases by ~2.8%. The benefits persist after CodeCacheSegmentSize changes from 64 back to 128.
> 
> Ran JTReg tier1 on Ampere-1A and no new issues were found.

Cool. I like the updates of rusty default settings is going on.

On https://github.com/openjdk/jdk/pull/20864 review comments we see that CodeEntryAlignment=16/32 was not good for AMPERE. Did you check both CPU_MODEL_AMPERE_1A/CPU_MODEL_AMPERE_1B CPUs? Are you sure the performance is good on all CPUs with 1A/1B cpu flag?

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PR Comment: https://git.openjdk.org/jdk/pull/22134#issuecomment-2490982607