RFR: 8267920: Create separate Events buffer for VMOperations [v3]

[Coleen Phillimore]

On Mon, 31 May 2021 11:17:44 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> The Events classes collect events in a circular buffer that gets dumped into the hs_err files. There are different sections to sort out different types of events. See:
>> 
>>   // A log for internal exception related messages, like internal
>>   // throws and implicit exceptions.
>>   static ExceptionsEventLog* _exceptions;
>> 
>>   // Deoptization related messages
>>   static StringEventLog* _deopt_messages;
>> 
>>   // Redefinition related messages
>>   static StringEventLog* _redefinitions;
>> 
>>   // Class unloading events
>>   static UnloadingEventLog* _class_unloading;
>> 
>> There's also a buffer for non-categorized events:
>> 
>>   // A log for generic messages that aren't well categorized.
>>   static StringEventLog* _messages;
>> 
>> I propose that we create a separate buffer for VMOperations. This will make it easier to debug GC related bugs.
>> 
>> With the proposed patch, the hs_err files will now have a section that looks like this.
>> 
>> VM Operations (20 events):
>> Event: 0,186 Executing VM operation: HandshakeAllThreads
>> Event: 0,186 Executing VM operation: HandshakeAllThreads done
>> Event: 0,230 Executing VM operation: ZMarkStart
>> Event: 0,230 Executing VM operation: ZMarkStart done
>> Event: 0,232 Executing VM operation: HandshakeAllThreads
>> Event: 0,232 Executing VM operation: HandshakeAllThreads done
>> Event: 0,232 Executing VM operation: HandshakeAllThreads
>> Event: 0,232 Executing VM operation: HandshakeAllThreads done
>> Event: 0,232 Executing VM operation: HandshakeAllThreads
>> Event: 0,233 Executing VM operation: HandshakeAllThreads done
>> Event: 0,233 Executing VM operation: ZMarkEnd
>> Event: 0,233 Executing VM operation: ZMarkEnd done
>> Event: 0,234 Executing VM operation: HandshakeAllThreads
>> Event: 0,234 Executing VM operation: HandshakeAllThreads done
>> Event: 0,234 Executing VM operation: ZVerify
>> Event: 0,234 Executing VM operation: ZVerify done
>> Event: 0,234 Executing VM operation: CleanClassLoaderDataMetaspaces
>> Event: 0,234 Executing VM operation: CleanClassLoaderDataMetaspaces done
>> Event: 0,235 Executing VM operation: ZRelocateStart
>> Event: 0,235 Executing VM operation: ZRelocateStart done
>
> Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Review tschatzl
>  - Merge remote-tracking branch 'origin/master' into 8267914_events_vmoperations
>  - Review coleenp
>  - 8267920: Create separate Events buffer for VMOperations

I think the way Stefan did it would make it easier to add Class Loading specific EventMark.
classfile/classLoader.cpp:  EventMark m("loading class %s", class_name);

Although I don't see any other EventMarks except for shenandoah GC.

So there could be future refactoring here.

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PR: https://git.openjdk.java.net/jdk/pull/4243