RFR: 6960970: Debugger very slow during stepping [v7]

Serguei Spitsyn sspitsyn at openjdk.org
Wed Dec 3 08:50:03 UTC 2025


> 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

Serguei Spitsyn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Merge
 - review: optimize hide_single_stepping and post_method_exit
 - review: renamed two functions; FRAME_POP_BIT removed from INTERP_EVENT_BITS
 - review: fix iteration order in process_vthread_pending_deopts as it uses remove_at(idx)
 - review: fix typo in a EATests.java comment
 - cleanup: removed an old code fragment in frame.cpp
 - 6960970: Debugger very slow during stepping

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28407/files
  - new: https://git.openjdk.org/jdk/pull/28407/files/bb4b11f9..abb1950c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28407&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28407&range=05-06

  Stats: 64652 lines in 1068 files changed: 42639 ins; 15493 del; 6520 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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