RFR: 8315884: New Object to ObjectMonitor mapping [v6]

[Daniel D. Daugherty]

On Mon, 15 Jul 2024 00:45:10 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> src/hotspot/share/runtime/lightweightSynchronizer.cpp line 401:
>> 
>>> 399: 
>>> 400:   if (inserted) {
>>> 401:     // Hopefully the performance counters are allocated on distinct
>> 
>> It doesn't look like the counters are on distinct cache lines (see objectMonitor.hpp, lines 212ff). If this is a concern, file a bug to investigate it later? The comment here is a bit misplaced, IMO.
>
> It originates from https://github.com/openjdk/jdk/blob/15997bc3dfe9dddf21f20fa189f97291824892de/src/hotspot/share/runtime/synchronizer.cpp#L1543 
> 
> I think we just kept it and did not think more about it.
> 
> Not sure what it is referring to. Maybe @dcubed-ojdk knows more, they originated from him (9 years old comment).

I don't think we ever got around to experimenting with putting the perf counters
on distinct cache lines. We've always had bigger fish to fry.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20067#discussion_r1715669185