RFR: 8277397: ZGC: Add JFR event for temporary latency measurements

[Jaroslav Bachorik]

On Thu, 18 Nov 2021 13:09:59 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> I often measure latencies and stalls using JFR events. I'd like to add an event that can be used for these ad-hoc measurements during development and debugging.

Changes requested by jbachorik (Reviewer).

src/hotspot/share/jfr/metadata/metadata.xml line 1037:

> 1035:   </Event>
> 1036: 
> 1037:   <Event name="ZThreadEvent" category="Java Virtual Machine, GC, Detailed" label="ZGC Thread Event" thread="true" experimental="true">

Can you add a description to the event?
For anyone coming from outside it would really help to understand what this event is supposed to represent.

src/jdk.jfr/share/conf/jfr/default.jfc line 778:

> 776:     </event>
> 777: 
> 778:     <event name="jdk.ZThreadEvent">

This is just a question - do we want/need to have this event enabled for the 'low overhead profiling' setup?

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PR: https://git.openjdk.java.net/jdk/pull/6454