March 2025 - hotspot-jfr-dev

Re: RFR: 8352251: Implement Cooperative JFR Sampling [v2]
by Markus Grönlund 28 Mar '25

28 Mar '25

> 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 incrementally with one additional commit since the last revision: refactoring ------------- Changes: - all: https://git.openjdk.org/jdk/pull/24296/files - new: https://git.openjdk.org/jdk/pull/24296/files/cb6e5aab..7998b7c1 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=24296&range=01 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24296&range=00-01 Stats: 218 lines in 8 files changed: 48 ins; 106 del; 64 mod Patch: https://git.openjdk.org/jdk/pull/24296.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24296/head:pull/24296 PR: https://git.openjdk.org/jdk/pull/24296

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RFR: 8348907: Stress times out when is executed with ZGC
by Markus Grönlund 26 Mar '25

26 Mar '25

Greetings, Here is a suggested solution for solving the intricate deadlock issues involving virtual threads, ZGC load barriers, and JFR. A JFR event can be allocated and committed in specific sensitive contexts, such as inside mutex-protected load barriers. If the thread is a virtual thread, JFR determines its thread name by loading the oop from the thread (jt->vthread()) as part of the event commit. This operation again triggers the load barrier, which contains a non-reentrant lock, effectively deadlocking the thread with itself. So, for specific sensitive event sites, JFR mustn't recurse or reenter into the same event site as part of the event commit. After a few iterations and prototypes, which failed because they eventually ended up touching some oop, I came up with the following. >From a user perspective, an event (site) can now be marked as "non-reentrant" by wrapping it in a helper class. This instruction now guarantees JFR will not reenter this site again as part of the event.commit(). The tradeoff is that we cannot write the virtual thread name for these sensitive event sites; we will instead report "" as the virtual thread name, which is the default virtual thread name in Java. All other information about the thread, such as the thread ID, virtual thread, etc., will still be reported. I believe it is a reasonable tradeoff and a general solution for sensitive JFR event sites, which are rare in practice, with minimal impact on event programming. Testing: jdk_jfr, stress testing Let me know what you think. Thanks Markus ------------- Commit messages: - 8348907 Changes: https://git.openjdk.org/jdk/pull/24209/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24209&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8348907 Stats: 160 lines in 10 files changed: 139 ins; 12 del; 9 mod Patch: https://git.openjdk.org/jdk/pull/24209.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24209/head:pull/24209 PR: https://git.openjdk.org/jdk/pull/24209

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RFR: 8352696: JFR: assert(false): EA: missing memory path
by Markus Grönlund 25 Mar '25

25 Mar '25

Greetings, In debug builds, we can sometimes assert because C2's Escape Analysis does not recognize a pattern where one input of memory Phi node is a MergeMem node, and another is a RAW store. This pattern is created by the jdk.jfr.internal.JVM.commit() intrinsic, which is inlined because of inlining JFR events, for example jdk.VirtualThreadStart. As a result, EA complains about a strange memory graph. Testing: jdk_jfr Thanks Markus ------------- Commit messages: - 8352696 Changes: https://git.openjdk.org/jdk/pull/24192/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24192&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8352696 Stats: 125 lines in 2 files changed: 121 ins; 1 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/24192.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24192/head:pull/24192 PR: https://git.openjdk.org/jdk/pull/24192

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RFR: 8352648: JFR: 'jfr query' should not be available in product builds
by Erik Gahlin 24 Mar '25

24 Mar '25

Could I have a review of a PR that removes the 'jfr query' command in product builds. The command was accidentally activated a couple of months ago, but it has never made it into a release. Testing: tier1 + test/jdk/jdk/jfr Thanks Erik ------------- Commit messages: - Initial Changes: https://git.openjdk.org/jdk/pull/24178/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24178&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8352648 Stats: 30 lines in 6 files changed: 26 ins; 0 del; 4 mod Patch: https://git.openjdk.org/jdk/pull/24178.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24178/head:pull/24178 PR: https://git.openjdk.org/jdk/pull/24178

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RFR: 8352096: Test jdk/jfr/event/profiling/TestFullStackTrace.java shouldn't be executed with -XX:+DeoptimizeALot
by Leonid Mesnik 17 Mar '25

17 Mar '25

The test create a lot of threads long stacks and overhead of often deoptimization with DeoptimizeALot causes timeouts. ------------- Commit messages: - test fixed Changes: https://git.openjdk.org/jdk/pull/24070/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24070&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8352096 Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/24070.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24070/head:pull/24070 PR: https://git.openjdk.org/jdk/pull/24070

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RFR: 8351995: JFR: Leftovers from removal of Security Manager
by Erik Gahlin 17 Mar '25

17 Mar '25

Could I have a review of a PR that removes leftovers from the removal of the Security Manager. Testing: jdk/jdk/jfr + tier1 Thanks Erik ------------- Commit messages: - Log exception on exit - Initial Changes: https://git.openjdk.org/jdk/pull/24044/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24044&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8351995 Stats: 129 lines in 7 files changed: 0 ins; 127 del; 2 mod Patch: https://git.openjdk.org/jdk/pull/24044.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24044/head:pull/24044 PR: https://git.openjdk.org/jdk/pull/24044

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RFR: 8352066: JVM.commit() and JVM.flush() exhibit race conditions against JFR epochs
by Markus Grönlund 17 Mar '25

17 Mar '25

Greetings, This change set removes some race conditions involving JFR epochs. For details, please see the JIRA issue. Testing: jdk_jfr, TestChunkIntegrity testing Thanks Markus ------------- Commit messages: - 8352066 Changes: https://git.openjdk.org/jdk/pull/24061/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24061&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8352066 Stats: 64 lines in 9 files changed: 5 ins; 36 del; 23 mod Patch: https://git.openjdk.org/jdk/pull/24061.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24061/head:pull/24061 PR: https://git.openjdk.org/jdk/pull/24061

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RFR: 8351999: JFR: Incorrect scaling of throttled values
by Erik Gahlin 17 Mar '25

17 Mar '25

Could I have a review of a PR that fixes an incorrect scaling of samples for the ThrottleSetting. Testing: jdk/jdk/jfr Thanks Erik ------------- Commit messages: - Initial Changes: https://git.openjdk.org/jdk/pull/24045/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24045&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8351999 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jdk/pull/24045.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24045/head:pull/24045 PR: https://git.openjdk.org/jdk/pull/24045

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RFR: 8351976: assert(vthread_epoch == current_epoch) failed: invariant
by Markus Grönlund 17 Mar '25

17 Mar '25

Greetings, This fix adjusts for an epoch mismatch for excluded virtual threads that become included after being mounted. The JIRA issue has more details. Testing: jdk_jfr, stress testing Thanks Markus ------------- Commit messages: - 8351976 Changes: https://git.openjdk.org/jdk/pull/24041/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24041&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8351976 Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jdk/pull/24041.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24041/head:pull/24041 PR: https://git.openjdk.org/jdk/pull/24041

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RFR: 8351967: JFR: Bug in AnnotationIterator
by Markus Grönlund 17 Mar '25

17 Mar '25

Greetings, A tiny adjustment to cover a corner case related to the processing of the RuntimeVisibleAnnotations attribute. Testing: jdk_jfr Thanks Markus ------------- Commit messages: - 8351967 Changes: https://git.openjdk.org/jdk/pull/24037/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24037&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8351967 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jdk/pull/24037.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24037/head:pull/24037 PR: https://git.openjdk.org/jdk/pull/24037

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