[jdk15u-dev] RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64

Fri Feb 25 12:14:05 UTC 2022

On Fri, 25 Feb 2022 10:24:08 GMT, Andrew Haley <aph at openjdk.org> wrote:

> So there are cases where it's worth using, but does this patch meet the "enhancement that provides substantial benefit to OpenJDK 11u users and it is of low risk" requirement?

This is for 15u not for 11u.

> Do you know of any applications that substantially benefit?

Yes, we have services which got improvements. Also 15u version of `java.util.concurrent.SynchronousQueue` uses `Thread.onSpinWait`. A SynchronousQueue microbenchmark (see it in https://bugs.openjdk.java.net/browse/JDK-8267502) got the following geomean ops/s when ran on 2 CPUs 60 times:
- No intrinsic implementation: 226,732.8 ops/s
- One ISB implementation: 1,996,916.3 ops/s

The difference is 8.8x.

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PR: https://git.openjdk.java.net/jdk15u-dev/pull/181