8321137: Reconsider ICStub alignment

[shipilev]

This continues from #16911. It initially started as performance optimization to compact ICStubs, but I think the safety arguments for fitting the ICStub per instruction cache line prevails. See bug and previous PR for more gory details. The footprint improvements on some architectures come as side-effect of untying the ICStub size from CodeEntryAlignment to (sometimes lower) cache line size.

Note that the size of ICStub is important, because ICBuffer is small (10K by default), and its depletion causes the ICBufferFull safepoint. I would make a (separate) argument to bump the default ICBuffer size a bit to make it less important.

Current patch affects ICStub size in different ways on different platforms, since current size is effectively 2xCodeEntryAlignment and new size is cache line size:

• ARM32: 32 -> 64 bytes :(
• AArch64: 128 -> 64 bytes :)
• x86_64: 64 -> 64 bytes :|
• x86_32: 32 -> 64 bytes :(
• PPC64: 512 -> 128 bytes :))
• RISC-V: 128 -> 64 bytes :)
• S390X: 128 -> 256 bytes :(
• Zero: <not applicable, Zero does not use IC stubs>

Additional testing:

• Linux x86_64 server fastdebug, tier{1,2,3,4}
• Linux AArch64 server fastdebug, tier{1,2,3,4}

---

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Issue

• JDK-8321137: Reconsider ICStub alignment (Enhancement - P4)

Reviewers

• Dean Long (@dean-long - Reviewer) ⚠️ Review applies to b0875b50
• Erik Österlund (@fisk - Reviewer) ⚠️ Review applies to b0875b50
• Martin Doerr (@TheRealMDoerr - Reviewer) ⚠️ Review applies to b0875b50
• Fei Yang (@RealFYang - Reviewer)
• Andrew Haley (@theRealAph - Reviewer)

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[mlbridge]

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• 02: Full - Incremental (d799cbb0)
• 01: Full - Incremental (b0875b50)
• 00: Full (c5c6398d)

[dean-long]

Nice job minimizing the changes.

[openjdk]

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

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

8321137: Reconsider ICStub alignment

Reviewed-by: dlong, eosterlund, mdoerr, fyang, aph

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 28 new commits pushed to the master branch:

• b891721: 8316756: C2 EA fails with "missing memory path" when encountering unsafe_arraycopy stub call
• bf666bc: 8322692: ZGC: avoid over-unrolling due to hidden barrier size
• de97c0e: 8290965: PPC64: Implement post-call NOPs
• f70667e: 8318112: CSS percentage values are capped at 100%
• 2063bb8: Merge
• bf7bd9a: 8317547: Enhance TLS connection support
• c1a568c: 8314307: Improve loop handling
• 1cc6fbd: 8318588: Windows build failure after JDK-8314468 due to ambiguous call
• ed238e8: 8314468: Improve Compiler loops
• fac49b8: 8317331: Solaris build failed with "declaration can not follow a statement (E_DECLARATION_IN_CODE)"
• ... and 18 more: https://git.openjdk.org/jdk/compare/8abaf119659e46684d196bf76784c11587039f60...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[shipilev]

Thanks @dean-long! Any other takers?

Notably, I would like opinions of platform maintainers: @theRealAph, @TheRealMDoerr, @RealFYang, @bulasevich.

[TheRealMDoerr]

It's probably good, but are you aware of the plans to remove the ICStubs completely? @fisk may have an opinion on it.

[shipilev]

It's probably good, but are you aware of the plans to remove the ICStubs completely? @fisk may have an opinion on it.

Yes, I did x86_32 version for Erik. I think we want something we can support in JDK update releases. I think the ICStub removal would not be backportable at all.

[TheRealMDoerr]

Ok. I think it's good for backports. I'll put it in our test queue.

[fisk]

Seems like a reasonable band-aid to backport. Looks good.

[TheRealMDoerr]

Test results are good. Thumbs up from my side!

[RealFYang]

LGTM. Also performed tier1-3 test with fastdebug build on linux-riscv64 platform.

[shipilev]

OK, thanks! I am going to merge it, and look for follow-ups, if any.

/integrate

[openjdk]

Going to push as commit 7be9f1d.
Since your change was applied there have been 31 commits pushed to the master branch:

• b8dafa6: 8323612: IOVecWrapper should be changed to be TerminatingThreadLocal
• f2a4ed6: 8323779: Serial: Remove Generation::promotion_attempt_is_safe
• 22642ff: 8319382: com/sun/jdi/JdwpAllowTest.java shows failures on AIX if prefixLen of mask is larger than 32 in IPv6 case
• b891721: 8316756: C2 EA fails with "missing memory path" when encountering unsafe_arraycopy stub call
• bf666bc: 8322692: ZGC: avoid over-unrolling due to hidden barrier size
• de97c0e: 8290965: PPC64: Implement post-call NOPs
• f70667e: 8318112: CSS percentage values are capped at 100%
• 2063bb8: Merge
• bf7bd9a: 8317547: Enhance TLS connection support
• c1a568c: 8314307: Improve loop handling
• ... and 21 more: https://git.openjdk.org/jdk/compare/8abaf119659e46684d196bf76784c11587039f60...master

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit 7be9f1d.

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