RFR: 8303210: [linux, Windows] Make UseSystemMemoryBarrier available as product flag [v5]

[Robbin Ehn]

On Tue, 28 Mar 2023 09:45:10 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> I'd like to enable UseSystemMemoryBarrier by default on supported Operating Systems in order to improve performance of thread state transitions (I/O, JNI, foreign function calls, JIT compiler threads, etc.). See JBS issue for more details.
>> Unfortunately, the feature was not yet implemented on all platforms. I added the code, but need the platform maintainers to check if it can be used reliably (and ideally if the performance improves). It's easy to switch it off again in case of problems.
>> 
>> Update: Startup performance and some benchmarks on some platforms are impacted (see below). So, this PR no longer switches it on by default.
>
> Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move flag configuration and initialization to os::init_2.

Marked as reviewed by rehn (Reviewer).

If there are performance regressions enabled it by default may not be the best thing for our users.

The issue in ContinuousCallSiteTargetChange.java is a bit worrying, since it concerns depots and transitions.

I don't mind this being a product flag.

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PR Review: https://git.openjdk.org/jdk/pull/12753#pullrequestreview-1360730051
PR Comment: https://git.openjdk.org/jdk/pull/12753#issuecomment-1486609137