RFR: JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort) [v15]

[Laurent Bourgès]

On Thu, 7 Jul 2022 15:58:33 GMT, iaroslavski <duke at openjdk.org> wrote:

>> Sorting:
>> 
>> - adopt radix sort for sequential and parallel sorts on int/long/float/double arrays (almost random and length > 6K)
>> - fix tryMergeRuns() to better handle case when the last run is a single element
>> - minor javadoc and comment changes
>> 
>> Testing:
>> - add new data inputs in tests for sorting
>> - add min/max/infinity values to float/double testing
>> - add tests for radix sort
>
> iaroslavski has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)
>   
>   * Added JMH

Here are JMH test results on my stable perf laptop (cpu fixed: 4 real cpu cores at 2ghz, HT disabled, i7 6820k):
https://github.com/bourgesl/bourgesl.github.io/blob/master/bench-220709-summary-2.log

It confirms Vladimir results: 50% gain in average in parallelSort(), huge gains (x5) on large random arrays...

As DPQS relies on ForkJoinPool.getCommonParallelism = 3 on my machine, MT speedup is only x3 ! 
I observed max 300%/400% cpu load when parallelSort() runs on large arrays...
Why does it return NCpuCore - 1 ?

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PR: https://git.openjdk.org/jdk/pull/3938