RFR: 8303210: [linux, Windows] Enable UseSystemMemoryBarrier by default if possible [v2]

[Martin Doerr]

On Sun, 26 Feb 2023 06:03:42 GMT, David Holmes <dholmes at openjdk.org> wrote:

> There are two steps needed here:
> 
> 1. An argument/justification that this move from being experimental to being product (even if diagnostic).
> 2. Enabling it by default.

Hi David, thanks for looking into this.
1. We want to support it in product JDKs. I think there has been enough testing to leave the experimental state. See https://github.com/openjdk/jdk/pull/12708#issuecomment-1442965746
2. We need it activated for customers to benefit from the performance improvement. In addition, I'd like to enable it as soon as possible in order to get additional testing before RDP1, also in EA builds. Switching it off again in case of any problems is very easy. Performance results were published here: https://github.com/openjdk/jdk/pull/10123#issuecomment-1235123012
In addition, performance measurements wrt. the foreign function interface (project Panama) have shown the memory barrier performance bottleneck.

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PR: https://git.openjdk.org/jdk/pull/12753