RFR: 8354517: Parallel: JDK-8339668 causes up to 3.7x slowdown in openjdk.bench.vm.gc.systemgc

[Thomas Schatzl]

On Thu, 22 May 2025 06:34:07 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Before JDK-8339668, full-gc marking array-chunk size uses `ObjArrayMarkingStride`. This patch restores the old behavior (performance).
> 
> The fix is extract out the chunk-size from `PartialArraySplitter` and use the either `ParGCArrayScanChunk` or `ObjArrayMarkingStride`, depending on the context -- the former is used during young-gc while the latter full-gc.
> 
> Test: tier1-3; checked perf regression is gone

Marked as reviewed by tschatzl (Reviewer).

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

PR Review: https://git.openjdk.org/jdk/pull/25382#pullrequestreview-2860243196