RFR: 8274615: Support relaxed atomic add for linux-aarch64

[David Holmes]

On Fri, 1 Oct 2021 05:04:45 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to the linux-aarch64 port to support relaxed
> atomic add operations.  Both ldxr/stxr and LSE-based implementations are
> provided. The appropriate one to use selected at runtime, using the existing
> infrastructure for that selection.
> 
> Testing:
> mach5 tier1-3
> Some hand-checked performance and functional testing that both LSE and
> non-LSE implementations work, and that the relaxed operations are faster
> than the conservative default.

Hi Kim,

Not an ARM expert but seeing as this just elides the dmb this looks fine.

Thanks,
David

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5785