Withdrawn: 8256265: G1: Improve parallelism in regions that failed evacuation

[duke]

On Wed, 12 Jan 2022 09:03:45 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Currently G1 assigns a thread per failed evacuated region. This can in effect serialize the whole process as often (particularly with region pinning) there is only one region to fix up.
> 
> This patch tries to improve parallelism when walking over the regions in chunks
> 
> Latest implementation scans regions in chunks to bring parallelism, it's based on JDK-8278917 which changes to uses prev bitmap to mark evacuation failure objs.
> 
> Here's the summary of performance data based on latest implementation, basically, it brings better and stable performance than baseline at "Post Evacuate Cleanup 1/remove self forwardee" phase. (Although some regression is spotted when calculate the results in geomean, becuase one pause time from baseline is far too small than others.)
> 
> The performance benefit trend is:
>  - pause time (Post Evacuate Cleanup 1) is decreased from 76.79% to 2.28% for average time, from 71.61% to 3.04% for geomean, when G1EvacuationFailureALotCSetPercent is changed from 2 to 90 (-XX:ParallelGCThreads=8)
>  - pause time (Post Evacuate Cleanup 1) is decreased from 63.84% to 15.16% for average time, from 55.41% to 12.45% for geomean, when G1EvacuationFailureALotCSetPercent is changed from 2 to 90 (-XX:ParallelGCThreads=<default=123>)
> ( Other common Evacuation Failure configurations are:
> -XX:+G1EvacuationFailureALot -XX:G1EvacuationFailureALotInterval=0 -XX:G1EvacuationFailureALotCount=0 )
> 
> For more detailed performance data, please check the related bug.

This pull request has been closed without being integrated.

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PR: https://git.openjdk.java.net/jdk/pull/7047