RFR: 8330198: Add some class loading related perf counters to measure VM startup [v10]

[David Holmes]

On Thu, 13 Jun 2024 05:00:33 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

>> Adding a few perf counters related to class loading to measure VM startup. The counters are only active if the user specifies `-Xlog:init` in the command line. A diagnostic flag `ProfileClassLinkage` is added to control the new counters. The flag is set to false by default and will be enabled if `-Xlog:init` is specified.
>> 
>> This change is already in the leyden/premain branch. There are more counters in the branch to measure other stuff. For now, just upstreaming class loader related counters.
>> 
>> Refer to the [comment](https://bugs.openjdk.org/browse/JDK-8330198?focusedId=14665311&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14665311) in the bug report for an example output.
>> 
>> Passed tiers 1 - 4 testing.
>
> Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:
> 
>   check log_is_enable() in ClassLoader::print_counters

Okay. But lets see if @iklam  is happy with where things ended up before integrating.

Thanks

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18790#pullrequestreview-2114999956