RFR: 8367378: GenShen: Missing timing stats when old mark buffers are flushed during final update refs

[Kelvin Nilsen]

On Thu, 11 Sep 2025 20:28:08 GMT, William Kemper <wkemper at openjdk.org> wrote:

> This change adds timing to the 'flush old SATB buffers' subphase of final update refs. Ultimately, we hope to move this phase to a handshake (or not have it all). In the interim, we should at least know how long it takes. The updated phase timings message in the logs has the form:
> 
> [2025-09-11T18:43:11.463+0000][291.626s][3541][info ][gc,stats       ] Pause Final Update Refs (N)         377 us, workers (us): ---, ---, ---, ---, ---, ---, ---, ---, 
> [2025-09-11T18:43:11.463+0000][291.626s][3541][info ][gc,stats       ]   Update Region States               98 us
> [2025-09-11T18:43:11.463+0000][291.626s][3541][info ][gc,stats       ]   Transfer Old From SATB             74 us
> [2025-09-11T18:43:11.463+0000][291.626s][3541][info ][gc,stats       ]   Trash Collection Set               48 us
> [2025-09-11T18:43:11.463+0000][291.626s][3541][info ][gc,stats       ]   Rebuild Free Set                  132 us
> [2025-09-11T18:43:11.463+0000][291.626s][3541][info ][gc,stats       ]   Propagate GC State                  6 us
> 
> The `Transfer Old From SATB` is new.

Thanks much

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Marked as reviewed by kdnilsen (Committer).

PR Review: https://git.openjdk.org/jdk/pull/27234#pullrequestreview-3213649690