8386637: PPC64: Implement Thread.onSpinWait() intrinsic and SpinPause using SMT priority hints

[dbriemann]

Benchmarking with ThreadOnSpinWaitProducerConsumer.java on Power10 with SMT8
have shown the following results:

Pinning the HW threads to the same core via taskset -c 0,2:
intrinsic disabled: 1490.2 us/op
intrinsic enabled: 340.3 us/op
=> 4.4x performance

Pinning the HW threads to different cores via taskset -c 0,8:
intrinsic disabled: 1047.8 µs/op
intrinsic enabled: 804.4 µs/op
=> 1.3x performance

Single hardware thread (taskset -c 0):
intrinsic disabled: 1614.9 µs/op
intrinsic enabled: 1863.3 µs/op
=> 0.87x performance (slight regression)

The slight regression on 1 HW thread seems negligible since that scenario is highly unlikely on modern processors.

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Integration blocker

 ⚠️ Title mismatch between PR and JBS for issue JDK-8386637

Issue

• JDK-8386637: PPC64: Implement Thread.onSpinWait() intrinsic and SpinPause() using SMT priority hints (Enhancement - P4) ⚠️ Title mismatch between PR and JBS.

Reviewers

• Martin Doerr (@TheRealMDoerr - Reviewer)

Reviewing

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[mlbridge]

Webrevs

• 00: Full (224f88b3)

[TheRealMDoerr]

LGTM.

[TheRealMDoerr]

Nice improvement! You need to fix the title mismatch (see above).