RFR: 8322732: ForkJoinPool may underutilize cores in async mode
Doug Lea
dl at openjdk.org
Sun May 12 13:08:14 UTC 2024
On Fri, 10 May 2024 12:20:27 GMT, Doug Lea <dl at openjdk.org> wrote:
>> src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 978:
>>
>>> 976: * of two, at least 2. See above.
>>> 977: */
>>> 978: static final int INITIAL_QUEUE_CAPACITY = 1 << 7;
>>
>> @DougLea Interesting change—what impact did you notice when doubling this?
>
> The goal is to reduce the worst form of contention: when queue arrays are laid out adjacently in memory. Increasing sizes has some impact but with diminishing returns. Thanks for the comment as a reminder that I haven't rechecked this lately in light of other layout changes. Will do.
After recheckiing, the best policy is to leave internal queues the same, but initialize external queues larger.
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PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1597634199
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