RFR: 8359110: Log accumulated GC and process CPU time upon VM exit [v2]

[Thomas Schatzl]

On Thu, 12 Jun 2025 13:35:51 GMT, Jonas Norlinder <duke at openjdk.org> wrote:

>> Add support to log CPU cost for GC during VM exit with `-Xlog:gc`.
>> 
>> 
>> [1.500s][info ][gc] GC CPU cost: 1.75%
>> 
>> 
>> Additionally, detailed information may be retrieved with `-Xlog:gc=trace`
>> 
>> 
>> [1.500s][trace][gc] Process CPU time: 4.945370s
>> [1.500s][trace][gc] GC CPU time: 0.086382s
>> [1.500s][info ][gc] GC CPU cost: 1.75%
>
> Jonas Norlinder has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Remove unused bool
>  - Refactor vtime logic in evaluate_operation into a stack object and call CPUTimeCounters without indirection

src/hotspot/share/gc/shared/collectedHeap.cpp line 234:

> 232:       cost = 100 * gc_vtime / process_vtime;
> 233:     }
> 234:     log_info(gc)("GC CPU cost: %2.2f%%", cost);

I would prefer "usage" instead of "cost". The former seems to be more neutral.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25779#discussion_r2142928706