[jdk17u-dev] RFR: 8307348: Parallelize heap walk for ObjectCount(AfterGC) JFR event collection [v2]

[Aleksey Shipilev]

On Wed, 5 Jul 2023 09:17:14 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Improves ObjectCount JFR events that take considerable time at GC pause. While the event is still heavy, the parallelization helps to avoid unnecessarily large stalls. 
>> 
>> The backport is not clean, because there are number of contextual differences: `WorkGang`, `WithUpdatedActiveWorkers` and other renames did not happen yet. I had to massage the patch to fit 17u better.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 fastdebug `jdk/jfr serviceability/sa`
>>  - [x] Linux x86_64 fastdebug `tier1 tier2 tier3`
>>  - [x] Linux AArch64 fastdebug `tier1 tier2 tier3`
>
> 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 one additional commit since the last revision:
> 
>   Backport 540c706bbcbb809ae1304aac4f2a16a5e83cb458

Re-checked the sanity test, 1G retained `Integer` objects, Mac M1:


# Before
[0.748s][debug][gc,phases  ] GC(4) Report Object Count 197.341ms
[5.511s][debug][gc,phases  ] GC(15) Report Object Count 962.337ms
[10.895s][debug][gc,phases  ] GC(20) Report Object Count 1448.222ms
[23.669s][debug][gc,phases  ] GC(26) Report Object Count 1110.162ms
[27.004s][debug][gc,phases  ] GC(27) Report Object Count 1173.298ms
[40.240s][debug][gc,phases  ] GC(33) Report Object Count 1122.373ms

# After
[0.190s][debug][gc,phases] GC(0) Report Object Count 1.054ms
[0.565s][debug][gc,phases  ] GC(5) Report Object Count 19.203ms
[1.230s][debug][gc,phases  ] GC(16) Report Object Count 82.339ms
[9.187s][debug][gc,phases  ] GC(23) Report Object Count 140.076ms
[11.521s][debug][gc,phases  ] GC(25) Report Object Count 160.064ms
[19.508s][debug][gc,phases  ] GC(30) Report Object Count 139.736ms
[21.547s][debug][gc,phases  ] GC(33) Report Object Count 174.721ms

Testing is clean. Push approval is here. Performs as expected.

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/1441#issuecomment-1623446630
PR Comment: https://git.openjdk.org/jdk17u-dev/pull/1441#issuecomment-1623447293