RFR: 8322732: ForkJoinPool may underutilize cores in async mode [v7]

[Viktor Klang]

On Wed, 29 May 2024 11:33:40 GMT, Doug Lea <dl at openjdk.org> wrote:

>> This set of changes address causes of poor utilization with small numbers of cores due to overly aggressive contention avoidance. A number of further adjustments were needed to still avoid most contention effects in deployments with large numbers of cores
>
> Doug Lea has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 41 additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - Add test for utilization with interdependent tasks
>  - Un-misplace onSpinWait call
>  - Adjust control flow
>  - Reduce memory stalls
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - More performance tradoffs
>  - Address review comments
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - Repack some fields; adjust control flow
>  - ... and 31 more: https://git.openjdk.org/jdk/compare/3d109313...cf5fe55c

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 2061:

> 2059:                 w.stackPred = (int)pc;           // set ctl stack link
> 2060:                 qc = (active & LMASK) | ((pc - RC_UNIT) & UMASK);
> 2061:                 if (pc == (pc = compareAndExchangeCtl(pc, qc)))

If I'm reading this right you might want to add a comment :)

Suggestion:

                if (pc == (pc = compareAndExchangeCtl(pc, qc))) // consistent

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PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1618974704