RFR: 8291753: Add JFR event for GC CPU Time

[Erik Gahlin]

On Fri, 12 Aug 2022 10:07:01 GMT, Sangheon Kim <sangheon.kim at oracle.com> wrote:

> No. This event is provided via GCTraceCPUTime class with GCTracer. And both ZGC and Shenanadoah are not using it. If you are suggesting to support all GCs, it is out of scope. It may be address as a separate enhancement.
> 

Thanks for the information.

Do you see any issues adding the event for those GCs (as a separate enhancement)? There are no limitation in the information the OS can provide (per thread) or how the GCs are implemented. The reason I am asking is because we want the design of the event to be future proof, so we don't end up with multiple GC CPU events. Users are likely to complain if the event is missing for some GCs. It seems like a very useful event, so I think the demand will be high for other GCs as well. Could you write in the event description which GCs that are supported?

An alternative would be to write the CPU usage as a percentage, similar to the CPULoad and ThreadCPU event. It would be a periodic event emitted every second and tools could display a graph of where the system is spending time. It could perhaps be complemented with a Compiler CPU event, as a separate enhancement.

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PR: https://git.openjdk.org/jdk/pull/9760