[jdk17u-dev] RFR: 8306738: Select num workers for safepoint ParallelCleanupTask [v4]

[Aleksey Shipilev]

On Mon, 19 Jun 2023 08:38:02 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Unclean backport to considerably improve the safepoint cleanup times. The backport is not clean, because the `WorkGang` -> `WorkerThreads` rename is missing. The is also the addition of `Dictionary::does_any_dictionary_needs_resizing` check, because JDK 17 is still have that resize code in JDK 17.
>> 
>> Additional testing:
>>  - [x] Ad-hoc benchmarks
>>  - [x] Linux x86_64 fastdebug `tier1 tier2 tier3`
>> 
>> The experiments (see original PR) show we win big on this:
>> ![plot](https://github.com/openjdk/jdk17u-dev/assets/1858943/fd69b925-fa69-4e13-ac8c-e0dd72dd43cd)
>
> Aleksey Shipilev 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 two additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8306738-safepoint-cleanup-num-workers
>  - Backport 672bade522b4641ffc30b0ac09791e8dcf21e003

The change was in mainline for over a month, with no ill effects reported.
This is an easy win for tail latencies caused by safepoint cleanups.
I would continue monitoring mainline for any related issues to this.

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/1379#issuecomment-1598304530