RFR: 8322732: ForkJoinPool may underutilize cores in async mode [v3]

[Viktor Klang]

On Wed, 22 May 2024 15:32:42 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 36 additional commits since the last revision:
> 
>  - 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
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - Next version
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - Reduce unneeded signals
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - ... and 26 more: https://git.openjdk.org/jdk/compare/d5552864...f1fc4f3e

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 1440:

> 1438:             while (task != null) {
> 1439:                 task.doExec();
> 1440:                 task = nextLocalTask(fifo);

Clean! 👍

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 1884:

> 1882:             else
> 1883:                 nc = (v.stackPred & LMASK) | (c & TC_MASK);
> 1884:             if (c == (c = compareAndExchangeCtl(c, nc | ac))) {

So the TTAS wasn't worth it on some architectures? 🤔

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PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1610244875
PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1610245643