RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v10]

[Nick Gasson]

On Tue, 12 Oct 2021 08:11:20 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Make OnSpinWaitInst/OnSpinWaitInstCount  DIAGNOSTIC
>
> Can we have a simple (as simple as possible) JMH benchmark, please? It should be something like a couple of threads racing to count up to a million.

> @theRealAph, any comments on the microbenchmark I wrote?

I think to show the benefit of the `onSpinWait()` changes you'd need some contention between the threads - e.g. if `nowork()` was updating a shared counter.

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PR: https://git.openjdk.java.net/jdk/pull/5562