8290688: Optimize x86_64 nmethod entry barriers

[fisk]

The current x86_64 nmethod entry barrier is good, but it could be a bit better. In particular, this enhancement targets the following ideas.

1. The alignment of the cmp instruction is 8 bytes. However, we only patch 4 bytes and the instruction length is always 8 bytes. So if we align the start of the instruction to 4 bytes only, that is enough to ensure that the immediate part of the instruction is 4 byte aligned, which is all we need (cf. http://cr.openjdk.java.net/~jrose/jvm/hotspot-cmc.html).

2. Today the fast path (conditionally) jumps over a call to a stub. It is not uncommon for the branch not taken path being better optimized, making it favourable to move the call to a stub out-of-line. This has the additional benefit of not polluting the instruction caches at the nmethod entry with instructions not used in the fast path. A bit messy but we can do it for at least C2 code.

3. For C1 and native wrappers, I don't think they are hot enough to warrant the stub machinery. But at least the jump that jumps over the cold stuff, can be shortened. I can get behind that.

Before addressing this, turning nmethod entry barriers on with G1 (e.g. by enabling loom) leads to a regression in DaCapo tradesoap-large. With this enhancement, the regression goes away, so that the cost of nmethod entry barriers is not visible.

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Progress

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Issue

• JDK-8290688: Optimize x86_64 nmethod entry barriers

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer)
• Richard Reingruber (@reinrich - Reviewer)

Reviewing

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[fisk]

/issue JDK-8290688

[openjdk]

@fisk The primary solved issue for a PR is set through the PR title. Since the current title does not contain an issue reference, it will now be updated.

[mlbridge]

Webrevs

• 03: Full - Incremental (c98b0753)
• 02: Full - Incremental (eeb5f82d)
• 01: Full - Incremental (a71e4ae7)
• 00: Full (2e8dd854)

[vnkozlov]

Looks good.

[openjdk]

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

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

8290688: Optimize x86_64 nmethod entry barriers

Reviewed-by: kvn, rrich

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At the time when this comment was updated there had been 43 new commits pushed to the master branch:

• 54854d9: 8256811: Delayed/missed jdwp class unloading events
• 75c1e99: 8289572: InputStream wrapping with BufferedInputStream is redundant in HttpTimestamper
• 7841e5c: 8290464: Optimize ResourceArea zapping on ResourceMark release
• e9f97b2: 8290489: Initial nroff manpage generation for JDK 20
• 59d85ba: 8290687: serviceability/sa/TestClassDump.java could leave files owned by root on macOS
• 66f59c2: 8290731: Clean up CDS handling of LambdaForm Species classes
• 0dda3c1: 8289275: Remove incorrect __declspec(dllimport) attributes from pointers in jdk.crypto.cryptoki
• 620c8a0: 8289643: File descriptor leak with ProcessBuilder.startPipeline
• 7ec0132: 8286844: com/sun/jdi/RedefineCrossEvent.java failed with 1 threads completed while VM suspended
• 80bd8c3: 8290504: Close streams returned by ModuleReader::list
• ... and 33 more: https://git.openjdk.org/jdk/compare/43c47b1ad7453b4be5ad949d49866de1d911973e...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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[fisk]

Looks good.

Thanks for the review, @vnkozlov!

[reinrich]

Hi Erik,

Looks good to me!

I can imagine that hot taken branches, especially many of them, can become a
performance issue when the hardware fails to predict the target address.

Richard.

[fisk]

Thanks for the review @reinrich!

[fisk]

/integrate

[openjdk]

Going to push as commit b28f9da.
Since your change was applied there have been 43 commits pushed to the master branch:

• 54854d9: 8256811: Delayed/missed jdwp class unloading events
• 75c1e99: 8289572: InputStream wrapping with BufferedInputStream is redundant in HttpTimestamper
• 7841e5c: 8290464: Optimize ResourceArea zapping on ResourceMark release
• e9f97b2: 8290489: Initial nroff manpage generation for JDK 20
• 59d85ba: 8290687: serviceability/sa/TestClassDump.java could leave files owned by root on macOS
• 66f59c2: 8290731: Clean up CDS handling of LambdaForm Species classes
• 0dda3c1: 8289275: Remove incorrect __declspec(dllimport) attributes from pointers in jdk.crypto.cryptoki
• 620c8a0: 8289643: File descriptor leak with ProcessBuilder.startPipeline
• 7ec0132: 8286844: com/sun/jdi/RedefineCrossEvent.java failed with 1 threads completed while VM suspended
• 80bd8c3: 8290504: Close streams returned by ModuleReader::list
• ... and 33 more: https://git.openjdk.org/jdk/compare/43c47b1ad7453b4be5ad949d49866de1d911973e...master

Your commit was automatically rebased without conflicts.

[openjdk]

@fisk Pushed as commit b28f9da.

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