> This change fixes a long standing performance issue related to the debugger 
> single stepping that is using JVMTI `FramePop` events as a part of step over 
> handling. The performance issue is that the target thread continues its 
> execution in very slow `interp-only` mode in a context of frame marked for 
> `FramePop` notification with the JVMTI `NotifyFramePop`. It includes other 
> method calls recursively upon a return from the frame.
> 
> This fix is to avoid enforcing the `interp-only` execution mode for threads 
> when `FramePop` events are enabled with the JVMTI 
> `SetEventNotificationMode()`. Instead, the target frame has been deoptimized 
> and kept interpreted by disabling `OSR` optimization by the function 
> `InterpreterRuntime::frequency_counter_overflow_inner()`. (Big thanks to 
> @fisk for this suggestion!) Additionally, some tweaks are applied in several 
> places where the `java_thread->is_interp_only_mode()` is checked.
> The other details will be provided in the first PR request comment.
> 
> Testing:
>  - test `serviceability/jvmti/vthread/ThreadStateTest` was updated to provide 
> some extra test coverage
>  - submitted mach5 tiers 1-6
> 
> - [x] I confirm that I make this contribution in accordance with the [OpenJDK 
> Interim AI Policy](https://openjdk.org/legal/ai).

Serguei Spitsyn has updated the pull request with a new target base due to a 
merge or a rebase. The pull request now contains 31 commits:

 - Merge
 - review: roll back unnneded minor refactoring
 - review: simplify deopt for virtual threads, get rid of pending deopts
 - Merge
 - review: 1. move set_frame_pop call; 2. decrease test execution time and its 
timeout
 - review: (1) remove unneeded assert, (2) simplify one statement in 
JvmtiEnvBase::set_frame_pop
 - update copyright year
 - review: (1) rename one method (2) remove unneeded changes
 - review: renamed test to StepOverStressTest.java
 - fix some merge error
 - ... and 21 more: https://git.openjdk.org/jdk/compare/9c3787d1...0956d877

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

Changes: https://git.openjdk.org/jdk/pull/28407/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28407&range=27
  Stats: 440 lines in 26 files changed: 328 ins; 48 del; 64 mod
  Patch: https://git.openjdk.org/jdk/pull/28407.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28407/head:pull/28407

PR: https://git.openjdk.org/jdk/pull/28407

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