RFR: 8330198: Add some class loading related perf counters to measure VM startup [v9]

[Calvin Cheung]

On Thu, 13 Jun 2024 02:19:16 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   remove log_vm_stats()
>
> src/hotspot/share/runtime/java.cpp line 362:
> 
>> 360:   if (log_is_enabled(Info, perf, class, link)) {
>> 361:       ClassLoader::print_counters(tty);
>> 362:   }
> 
> Again this needs to comment why we check the log is active but write to tty instead of the logstream.
> 
> Or we could put the `log_is_enabled` check inside `print_counters` rather than require callers to do it. That also allows us to print that the counters are disabled eg.
> 
> void ClassLoader::print_counters(outputStream *st) {
>   // The counters are only active if the logging is enabled, but
>   // we print to the passed in outputStream as requested.
>   if (log_is_enabled(Info, perf, class, link)) {
>     st->print_cr("ClassLoader:");
>     ...
>   } else {
>     st->print_cr("ClassLoader: <not enabled>");
>   }

I've made the above changes as you suggested without the else part to be consistent with printing of other statistics.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18790#discussion_r1637537375