On Sat, 20 Sep 2025 04:40:16 GMT, Serguei Spitsyn <[email protected]> wrote:
> This update removes a significant performance overhead when an application > running millions of virtual threads is started with the JDWP agent but > debugger has not been attached. The overhead is 4X-6X slowdown. > The tested app normally (without debug agent) takes around 3+ seconds. With > debug agent enabled it takes 14 seconds and more. The performance overhead is > caused by the `jvmti_yield_cleanup()` recursively calling > `JvmtiExport::continuation_yield_cleanup()`. The reason of this overhead is > because the function `JvmtiExport::can_post_frame_pop()` is used to identify > a need for the JVMTI cleanup which is not precise and triggers unneeded work > when debugger has not been attached yet. The fix is to trigger the JVMTI > cleanup with new function: `bool JvmtiExport::has_frame_pops(JavaThread* > thread)`. > > Testing: > - Insure the 4X-6X slowdown is gone for an application running millions of > virtual threads and started with JDWP agent > - Mach5 tiers 1-6 are all passed This pull request has now been integrated. Changeset: 17244c69 Author: Serguei Spitsyn <[email protected]> URL: https://git.openjdk.org/jdk/commit/17244c699ad20fafe7448678a53266ce6bf017e5 Stats: 24 lines in 3 files changed: 18 ins; 1 del; 5 mod 8368159: Significant performance overhead when started with jdwp agent and unattached debugger Reviewed-by: lmesnik, cjplummer ------------- PR: https://git.openjdk.org/jdk/pull/27403
