RFR: 8368715: Serial: Add GCTraceTime for marking from roots subphases during full gc marking [v2]

[Albert Mingkun Yang]

On Fri, 26 Sep 2025 07:35:09 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Add a scoped timer for the first subphase of marking, to be aligned with other counterparts.
>> 
>> Test: tier1-5
>
> Albert Mingkun Yang 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:
> 
>   sgc-scope-mark

Thanks for review.

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PR Comment: https://git.openjdk.org/jdk/pull/27499#issuecomment-3345424899