RFR: 8346470: Improve WriteBarrier JMH to have old-to-young refs [v2]

[Eric Caspole]

On Thu, 13 Mar 2025 15:53:43 GMT, Eric Caspole <ecaspole at openjdk.org> wrote:

>> Adds new cases based on the existing ones using an extra iteration setup to allocate into young gen, allowing to test old-to-young stores etc, where the existing code is all old-to-old.
>> 
>> Here is a run on a standard OCI A1.160 with JDK 25:
>> 
>> Benchmark                                                                         Mode  Cnt     Score    Error  Units
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathNullLarge          avgt   12  3448.826 ±  1.620  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathNullSmall          avgt   12    63.740 ±  0.151  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathNullYoungLarge     avgt   12  3448.353 ±  0.860  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathNullYoungSmall     avgt   12    63.565 ±  0.132  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathOldToYoungLarge    avgt   12  4476.390 ±  0.930  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathOldToYoungSmall    avgt   12    73.517 ±  0.082  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathRealLarge          avgt   12  3103.911 ±  2.079  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathRealSmall          avgt   12    57.549 ±  0.512  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathYoungToOldLarge    avgt   12  9587.762 ±  2.044  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathYoungToOldSmall    avgt   12   157.244 ±  0.169  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathYoungToYoungLarge  avgt   12  3103.191 ±  1.100  ns/op
>> WriteBarrier.WithDefaultUnrolling.testArrayWriteBarrierFastPathYoungToYoungSmall  avgt   12    57.392 ±  0.624  ns/op
>> WriteBarrier.WithDefaultUnrolling.testFieldWriteBarrierFastPath                   avgt   12     2.668 ±  0.001  ns/op
>> WriteBarrier.WithDefaultUnrolling.testFieldWriteBarrierFastPathYoungRef           avgt   12     9.337 ±  0.001  ns/op
>> WriteBarrier.WithoutUnrolling.testArrayWriteBarrierFastPathNullLarge              avgt   12  3449.234 ±  1.840  ns/op
>> WriteBarrier.WithoutUnrolling.testArrayWriteBarrierFastPathNullSmall              avgt   12    63.720 ±  0.079  ns/op
>> WriteBarrier.WithoutUnrolling.testArrayWriteBarrierFastPathNullYoungLarge         avgt   12  3448.055 ±  0.665  ns/op
>> WriteBarrier.WithoutUnrolling.testArrayWriteBarrierFastPathNullYoungSmall         avgt   1...
>
> Eric Caspole has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Update test/micro/org/openjdk/bench/vm/compiler/WriteBarrier.java
>    
>    Co-authored-by: Thomas Schatzl <59967451+tschatzl at users.noreply.github.com>
>  - Update test/micro/org/openjdk/bench/vm/compiler/WriteBarrier.java
>    
>    Co-authored-by: Thomas Schatzl <59967451+tschatzl at users.noreply.github.com>

Updated the code with Thomas' suggestions.

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PR Comment: https://git.openjdk.org/jdk/pull/24010#issuecomment-2721751933