8329726: Use non-short forward jumps in lightweight locking #18657

rkennke · 2024-04-05T13:33:33Z

This turns a few short-jumps to long-jumps in x86 lightweight locking code paths. When running with -XX:+ShowMessageBoxOnError, MA::stop() generates more code and jccb is not sufficient to address this.

Two of the jccb are in ASSERT path anyway. However, another is also in a product path. We could generate jccb or jcc conditionally on ShowMessageBoxOnError, however, I don't think it is worth the trouble. WDYT?

Unfortunately, I could not make a simple test-case, because ShowMessageBoxOnError stops and waits on error, which would make jtreg time-out.

Testing:

manual test with dacapo as provided in the bug report
tier1

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Issue

JDK-8329726: Use non-short forward jumps in lightweight locking (Bug - P3)

Reviewers

Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to f6231d8f
Vladimir Kozlov (@vnkozlov - Reviewer) ⚠️ Review applies to 025755b2
Axel Boldt-Christmas (@xmas92 - Reviewer) ⚠️ Review applies to f6231d8f

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bridgekeeper · 2024-04-05T13:34:29Z

👋 Welcome back rkennke! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2024-04-05T13:35:09Z

@rkennke This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8329726: Use non-short forward jumps in lightweight locking

Reviewed-by: shade, kvn, aboldtch

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At the time when this comment was updated there had been 18 new commits pushed to the master branch:

6439375: 8329533: TestCDSVMCrash fails on libgraal
3ebf8c9: 8329663: hs_err file event log entry for thread adding/removing should print current thread
be45de1: 8328627: JShell documentation should be clearer about "remote runtime system"
8648890: 8329749: Obsolete the unused UseNeon flag
fc18201: 8327111: Replace remaining usage of create_bool_from_template_assertion_predicate() which requires additional OpaqueLoop*Nodes transformation strategies
7c66465: 8325088: Overloads that differ in type parameters may be lost
6f087cb: 8328698: oopDesc::klass_raw() decodes without a null check
d1aad71: 8321204: C2: assert(false) failed: node should be in igvn hash table
51b0abc: 8329340: Remove unused libawt code
3a3b77d: 8329641: RISC-V: Enable some tests related to SHA-2 instrinsic
... and 8 more: https://git.openjdk.org/jdk/compare/27353ad367c2342086d8e56ee2412d796d44b664...master

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openjdk · 2024-04-05T13:35:44Z

@rkennke The following label will be automatically applied to this pull request:

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mlbridge · 2024-04-05T13:38:19Z

Webrevs

shipilev

Sad to give up a short jump in synchronization code just for asserts. Maybe we give up on code readability a bit? E.g.:

#ifdef ASSERT
  // Check that locked label is reached with ZF set.
  Label zf_bad_zero, zf_correct;
  jcc(Assembler::zero, zf_correct);
  jmp(zf_bad_zero)
#endif

  bind(slow_path);

#ifdef ASSERT
  // Check that slow_path label is reached with ZF not set.
  jccb(Assembler::notZero, zf_correct);
  stop("Fast Lock ZF != 0");
  bind(zf_bad_zero);
  stop("Fast Lock ZF != 1");
  bind(zf_correct);
#endif

vnkozlov

Good.

TobiHartmann · 2024-04-08T05:06:28Z

Unfortunately, I could not make a simple test-case, because ShowMessageBoxOnError stops and waits on error, which would make jtreg time-out.

Although a time out is a bit of a confusing failure mode for the test, I think it would be better than no test at all, right?

rkennke · 2024-04-08T08:15:59Z

Unfortunately, I could not make a simple test-case, because ShowMessageBoxOnError stops and waits on error, which would make jtreg time-out.

Although a time out is a bit of a confusing failure mode for the test, I think it would be better than no test at all, right?

Right. I added a test-case with a short timeout. It fails without the change, and passes with it.

xmas92

lgtm.

rkennke · 2024-04-08T10:34:22Z

@TobiHartmann could you check the test? I am not sure if the flags are reasonable.

TobiHartmann · 2024-04-08T11:54:10Z

Looks good but I think it's safer to use the default timeout because otherwise we risk a false-positive timeout on slow machines when running with additional flags like -XX:+DeoptimizeALot.

rkennke · 2024-04-09T14:50:04Z

/integrate

openjdk · 2024-04-09T14:50:43Z

Going to push as commit 2e925f2.
Since your change was applied there have been 48 commits pushed to the master branch:

e75e1cb: 8329955: Class-File API ClassPrinter does not print bootstrap methods arguments
f9bc2db: 8325371: Missing ClassFile.Option in package summary
a8fbeec: 8329956: G1: Remove unimplemented collection_set_candidate_short_type_str
3b6629c: 8324673: javacserver failed during build: RejectedExecutionException
5fb5e6c: 8329603: G1: Merge G1BlockOffsetTablePart into G1BlockOffsetTable
2fcb816: 8305072: Win32ShellFolder2.compareTo is inconsistent
635cb3c: 8329745: Update the documentation of ServerSocket and Socket to refer to StandardSocketOptions instead of legacy SocketOptions
5c9f036: 8329858: G1: Make G1VerifyLiveAndRemSetClosure stateless
492b954: 8329750: Change Universe functions to return more specific Klass* types
87131fb: 8329629: GC interfaces should work directly against nmethod instead of CodeBlob
... and 38 more: https://git.openjdk.org/jdk/compare/27353ad367c2342086d8e56ee2412d796d44b664...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-04-09T14:50:48Z

@rkennke Pushed as commit 2e925f2.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8329726: Use non-short forward jumps in lightweight locking

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openjdk bot added the rfr Pull request is ready for review label Apr 5, 2024

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Apr 5, 2024

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Shuffle code to preserve short-jump on non-assert paths

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Add test-case

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Use default timeout for test

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