jmx-dev RFR: 8368527: JMX: Add an MXBeans method to query GC CPU time

[Kevin Walls]

On Tue, 30 Sep 2025 09:25:24 GMT, Jonas Norlinder <duke at openjdk.org> wrote:

>> It’s mostly about making clear it’s Not a measurement for pause time (no matter if wall clock or per thread), dont know how to best Formulate it. I think it’s needed sind typically pause times have been associated with GRC thread Timings. Maybe something like „the accounted CPU time can be spent concurrently with application threads or during pauses“ or something Like that?
>
> In the CSR discussion I proposed changing the method name to `getTotalGcCpuTime()` as @kevinjwalls raised concerns about conflating it with per generation CPU timings. Would the renaming to `getTotalGcCpuTime()` also solve your concern here?

Also, genesis (Universe::genesis()?), is a VM detail that may be unclear.  Do we mean:
"
Returns the CPU time used by all garbage collection threads.

This includes time for all driver threads, workers, VM operations
on the VM thread, and the string deduplication thread (if enabled). 
Therefore the value can be non-zero even if no garbage collection cycles have occurred. 

This method returns {@code -1} if the platform does not support this operation, or if called during shutdown.
"

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PR Review Comment: https://git.openjdk.org/jdk/pull/27537#discussion_r2390853215