RFR: 8292266: Add JFR event for total Reference processing time [v3]

[Sangheon Kim]

On Fri, 18 Nov 2022 19:43:13 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Sangheon Kim has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update src/hotspot/share/jfr/metadata/metadata.xml
>>   
>>   Co-authored-by: Thomas Schatzl <59967451+tschatzl at users.noreply.github.com>
>
> src/hotspot/share/gc/shared/gcTrace.cpp line 76:
> 
>> 74:   send_reference_stats_event(REF_PHANTOM, rps.phantom_count());
>> 75: 
>> 76:   send_reference_process_time_event(rps.total_process_time());
> 
> I think this is called by all collectors, but Z and Shenandoah would have zero for "total process time" here. I am not sure if this causes confusion on reading the jfr reports.

You are right and this is current scope of this CR.
If both collectors measure spent time, we can add it later. Hopefully under separate CR.

Or if the confusion only comes from zero value of the measured time, we can avoid sending zero value event. i.e. skip sending ref-proc-time event for both collectors. 
My first commit is something like this but stopped as someone may complain lack of the event anyway.

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PR: https://git.openjdk.org/jdk/pull/11230