RFR: 8365153: AArch64: Set JVM flags for Neoverse N3 and V3 cores

[Evgeny Astigeevich]

On Fri, 8 Aug 2025 14:50:13 GMT, Ruben <duke at openjdk.org> wrote:

> For Neoverse N1, N2, V1, and V2, the following JVM flags are set:
>  - UseSIMDForMemoryOps=true
>  - OnSpinWaitInst=isb
>  - OnSpinWaitInstCount=1
>  - AlwaysMergeDMB=false
> 
> Additionally, for Neoverse V1 and V2 only, these flags are set:
>  - UseCryptoPmullForCRC32=true
>  - CodeEntryAlignment=32
> 
> Set the same flags for Neoverse N3 and V3, respectively.

Neoverse-N3:

> UseSIMDForMemoryOps=true

When it's true we use `ldpq/stpq`. N3 `ldpq` latency/throughput is the same as N2. N3 `stpq` latency/throughput is 2/2. N2 `stpq` latency/throughput is 2/1. So we might expect better performance on N3.

 > OnSpinWaitInst=isb
OnSpinWaitInstCount=1
AlwaysMergeDMB=false

IMO we should not expect big changes here as well.

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PR Comment: https://git.openjdk.org/jdk/pull/26701#issuecomment-3312885831