RFR: 6203: Add ZGC allocation stall rule [v3]

[Marcus Hirt]

On Wed, 27 Aug 2025 20:10:20 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> Suchita Chaturvedi has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
>> 
>>  - Resolving merge conflict
>>  - Updated the rule as per new metric allocation stall rate
>>  - 6203: Add ZGC allocation stall rule
>
> core/org.openjdk.jmc.flightrecorder.rules.jdk/src/main/java/org/openjdk/jmc/flightrecorder/rules/jdk/memory/ZGCAllocationStallRule.java line 139:
> 
>> 137: 
>> 138: 			//Calculate time after JVM Start
>> 139: 			IQuantity timeAfterJVMStart = RulesToolkit.getEarliestStartTime(items)
> 
> Come to think of it - this will not work well for OldObjectSample events. They are a bit special and may be timestamped far earlier than the current recording period. I think we might want to add a RulesToolkit function that explicitly avoid the OldObjectSample events for this...

Suchita - I checked the jdk.OldObjectSample event after your slack message, and it turns out that there is a separate allocationTime for that event, so this isn't a problem. The timestamp on the events seem to be from the time of emission, so it should be all good.

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PR Review Comment: https://git.openjdk.org/jmc/pull/664#discussion_r2319898491