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/1dc80514...cf5fe55c

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 2094:

> 2092:                         if (((p = w.phase) & IDLE) != 0)
> 2093:                             p = awaitWork(w, delay); // block, drop, or exit
> 2094:                     }

I'm presuming the code below would be equivalent but avoid calculating the delay unless w.phase is IDLE?

Suggestion:

                    if ((p & IDLE) != 0 && ((p = w.phase) & IDLE) != 0) {
                        long delay = (((qc & RC_MASK) > 0L) ? 0L :
                                      (w.source != INVALID_ID) ? keepAlive :
                                      TIMEOUT_SLOP); // minimal delay if cascade
                        p = awaitWork(w, delay); // block, drop, or exit
                    }

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1618980694