RFR: 8322535: Change default AArch64 SpinPause instruction

[Evgeny Astigeevich]

On Tue, 16 Jan 2024 10:18:26 GMT, Andrew Haley <aph at openjdk.org> wrote:

> ISB isn't really the right thing for this. Sure, it causes a delay, but the extent of the delay depends on what else the processor is doing. In some cases an ISB can work well, in other cases not. Some micro benchmarks show a great improvement with ISB. It doesn't depend only on the target hardware, but on the application. Sure, in some cases an ISB is going to be exactly right, but on others it might be too much.

BTW, In Armv8.7-A/Armv9.2-A  we have WFE/WFI with timeouts which is supported by Cortex-X4, A720 and A520. Available implementations of them are MediaTek Dimensity 9300 and Qualcomm Snapdragon 8 Gen 3. It would be possible to benchmark WFE-based implementation.

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PR Comment: https://git.openjdk.org/jdk/pull/17430#issuecomment-1893795630