RFR: 8352251: Implement Cooperative JFR Sampling [v16]

[Markus Grönlund]

On Mon, 5 May 2025 08:50:35 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> Greetings,
>> 
>> This is the implementation of JEP [JDK-8350338 Cooperative JFR Sampling](https://bugs.openjdk.org/browse/JDK-8350338).
>> 
>> Implementations in this change set are provided and have been tested on the following platforms:
>> 
>> - windows-x64
>> - windows-x64-debug
>> - linux-x64
>> - linux-x64-debug
>> - macosx-x64
>> - macosx-x64-debug
>> - linux-aarch64
>> - linux-aarch64-debug
>> - macosx-aarch64
>> - macosx-aarch64-debug
>> 
>> Testing: tier1-6, jdk_jfr, stress testing.
>> 
>> Platform porters note:
>> Some platform-specific code needs to be provided, mainly in the interpreter. Take a look at the following files for changes:
>> 
>> - src/hotspot/cpu/x86/frame_x86.cpp
>> - src/hotspot/cpu/x86/interp_masm_x86.cpp
>> - src/hotspot/cpu/x86/interp_masm_x86.hpp
>> - src/hotspot/cpu/x86/javaFrameAnchor_x86.hpp
>> - src/hotspot/cpu/x86/macroAssembler_x86.cpp
>> - src/hotspot/cpu/x86/macroAssembler_x86.hpp
>> - src/hotspot/cpu/x86/templateInterpreterGenerator_x86.cpp
>> - src/hotspot/cpu/x86/templateTable_x86.cpp
>> - src/hotspot/os_cpu/linux_x86/javaThread_linux_x86.hpp
>> 
>> Thanks
>> Markus
>
> Markus Grönlund has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 19 commits:
> 
>  - Merge branch 'master' into 8352251
>  - Configuration and test for jdk.SafepointLatency event
>  - include guards
>  - push back pd constants into pd code
>  - Attempt to build Windows-AARCH64
>  - No invariants for sender_for_interpreter_frame
>  - zero
>  - Merge branch 'master' into 8352251
>  - Refine SamplingLatency event description
>  - Update default.jfc
>  - ... and 9 more: https://git.openjdk.org/jdk/compare/8511220f...e448090e

> > Can we let _last_sender_Java_fp be a state field that can be tested?
> 
> I still couldn't hit any failures or errors with my simple version, but I understand that it might be problematic.
> 
> I have an implementation: [TheRealMDoerr at b2f83fa](https://github.com/TheRealMDoerr/jdk/commit/b2f83fae262f129f864e109d7adce169e28f0c7c) Please take a look. I hope we don't need more ;-) I'm planning to run more test when I find more time.
> 
> If `_last_sender_Java_fp` is needed on all platforms, shouldn't it be better moved to shared javaFrameAnchor.hpp and javaThread.hpp?

That is a good reflection. I followed _last_java_FP which is defined in platform specific files. Are we not using _last_java_FP on all platforms?

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PR Comment: https://git.openjdk.org/jdk/pull/24296#issuecomment-2851761291