RFR: 8368159: Significant performance overhead when started with jdwp agent and unattached debugger [v2]

[Chris Plummer]

On Wed, 24 Sep 2025 21:38:58 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>>> The interp_only check is needed for optimization to avoid a performance overhead of current stack depth invalidation.
>> 
>> But if we are not in interp_only mode isn't it already invalidated?
>
>> But if we are not in interp_only mode isn't it already invalidated?
> 
> It does not need to be invalidated if not in `interp_only` mode as it should not be used there or has to be explicitly invalidated exactly where it is needed. The issue I see is only with the test `test/hotspot/jtreg/serviceability/jvmti/vthread/ContStackDepthTest` which is for plain Continuations. Otherwise, the `invalidate_jvmti_stack()` would not be needed. It plays as a workaround to make this test to pass. It seems there is a bug related to plain Continuations lurking somewhere.

My point is we could just unconditionally invalidate. It would do no harm. It would not be invalidating a curr stack depth that could later be used.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27403#discussion_r2377189171