RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v48]

[Man Cao]

On Mon, 4 Dec 2023 13:07:15 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

>> In the interest of the RDP1 deadline, should we leave improving the sync issues with gc_total to a separate RFE? (Especially given that a "correct" design may take some time to come up with, and that gc_total being slightly out of sync is not a major issue.)
>
> Me and Albert discussed this again and we are ok with handling the `gc_total` sync issue as a follow up. Please create the RFE for that. If that would include needing a `PerfAtomicCounter`, that would a be its own RFE as well. For me I think a lock would be a good enough solution. 
> 
> From our point of view having the counters out of sync for a long period of time (think a long concurrent mark cycle without any young collections updating the total) is not good since it shows that the counters are not incremented in sync. It would also be nice to avoid the two-step updating of the total time, so please try to find time to work on this.

Thanks, opened https://bugs.openjdk.org/browse/JDK-8321304.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/15082#discussion_r1414634977