RFR: 8362193: Re-work MacOS/AArch64 SpinPause to handle SB

[Andrew Haley]

On Fri, 25 Jul 2025 19:43:26 GMT, Evgeny Astigeevich <eastigeevich at openjdk.org> wrote:

> In Apple Silicon CPU Optimization Guide I found M4 supports FEAT_SB (Armv8.5-A), FEAT_ECV (Armv8.6-A) and FEAT_WFxT (Armv8.7-A). I will try to get access to it to test the implementation.

Unfortunately, it seems that Apple silicon runs the Arm Generic Timer at 24 Mhz, which I suspect is much too coarse for this use. It might work, but if it doesn't we could use the same algorithm with a spin loop.

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PR Comment: https://git.openjdk.org/jdk/pull/26387#issuecomment-3127956749