RFR: 8350285: Regression caused by ShenandoahLock under extreme contention

[Xiaolong Peng]

On Wed, 19 Feb 2025 18:29:04 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

>> I looked around HS sources, and I think the closest primitive we have is `HandshakeSpinYield`, which does 10us sleeps. How much worse is 10us in comparison to 100us in your tests? I would prefer to do 10us for all platforms, if performance tests allow us. This would also allow you to inline `short_sleep()`.
>
> It is like more than 2x worse, but still much better(10x) than tip and revert of JDK-8331411, here are the top 10 at-safepoint time for comparison:
> 10 us:
> 
> 7982953
> 5043319
> 5008139
> 4597156
> 4580556
> 4429245
> 4403175
> 4047891
> 3677389
> 3582308
> 
> 
> 100 us:
> 
> 4553716
> 1703093
> 1046248
> 1038148
> 780447
> 778786
> 778436
> 778276
> 728716
> 721856
> 
> 
> I can change it to same seep time for all platforms, but Windows doesn't really support nanosecond resolution sleep, JVM use combination of yield and spin pause to approximate nanosecond resolution sleep for Windows, it should be still fine since it won't be worse then only `yield` as before. In short, I am not expecting any improvement for Windows.

I have changed to be same for all platforms, but still keep 100us sleep duration given that it did perform better.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23701#discussion_r1962203617