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8280867: Cpuid1Ecx feature parsing is incorrect for AMD CPUs #7287

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@shipilev shipilev commented Jan 31, 2022

See discussion in the bug. AFAICS, the fix is to "just" shift the flags by one to match both Intel and AMD specs. I believe this is not a serious bug, because adjacent bits in AMD case are set on modern chips, and Intel detection code only uses lzcnt and prefetchw out of these flags, both with Intel-specific hacks that are dropped now.

Additional testing:

  • Linux x86_64 fastdebug on TR 3970X (Zen 2)
  • Linux x86_64 fastdebug on i5-11500 (Rocket Lake)
  • Eyeballing -Xlog:os+cpu on TR 3970X (Zen 2) -- no change in detected flags
  • Eyeballing -Xlog:os+cpu on i5-11500 (Rocket Lake) -- no change in detected flags

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  • JDK-8280867: Cpuid1Ecx feature parsing is incorrect for AMD CPUs

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👋 Welcome back shade! 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.

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

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@openjdk openjdk bot added the hotspot hotspot-dev@openjdk.org label Jan 31, 2022
@shipilev shipilev changed the title 8280867: AMD CPU feature flags handling is incorrect 8280867: Cpuid1Ecx feature parsing is incorrect for AMD CPUs Jan 31, 2022
@shipilev shipilev marked this pull request as ready for review January 31, 2022 13:13
@openjdk openjdk bot added the rfr Pull request is ready for review label Jan 31, 2022
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Webrevs

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Right. In Intel's manual:

CPUID.(EAX=8000_0001H):ECX[bit 5]=1 indicates LZCNT is supported.
CPUID.(EAX=8000_0001H):ECX[bit 8]=1 indicates PREFETCHW is supported.

From AMD's

ECX[bit 5]=1 ABM: advanced bit manipulation. LZCNT instruction support.
ECX[bit 6]=1 SSE4A: EXTRQ, INSERTQ, MOVNTSS, and MOVNTSD instruction support.
ECX[bit 7]=1 MisAlignSse: misaligned SSE mode.
ECX[bit 8]=1 3DNowPrefetch: PREFETCH and PREFETCHW instruction support.

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openjdk bot commented Jan 31, 2022

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

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

8280867: Cpuid1Ecx feature parsing is incorrect for AMD CPUs

Reviewed-by: kvn, dlong

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 37 new commits pushed to the master branch:

  • 4191b2b: 8275337: C1: assert(false) failed: live_in set of first block must be empty
  • 96d0df7: 8272984: javadoc support for reproducible builds
  • ee3be0b: 8280488: doclint reference checks withstand warning suppression
  • 74921e8: 8280738: Minor cleanup for HtmlStyle
  • 3916561: 8280543: Update the "java" and "jcmd" tool specification for CDS
  • f991891: 8280949: Correct the references for the Java Security Standard Algorithm Names specification
  • 319b774: 8277101: jcmd VM.cds dynamic_dump should not regenerate holder classes
  • 993a248: 8280450: Add task queue printing to STW Full GCs
  • dcc666d: 8280139: Report more detailed statistics about task stealing in task queue stats
  • bdda43e: 8280705: Parallel: Full gc mark stack draining should prefer to make work available to other threads
  • ... and 27 more: https://git.openjdk.java.net/jdk/compare/cab590517bf705418c7376edd5d7066b13b6dde8...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.

@openjdk openjdk bot added the ready Pull request is ready to be integrated label Jan 31, 2022
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shipilev commented Feb 1, 2022

Right, thanks for reviews!

/integrate

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openjdk bot commented Feb 1, 2022

Going to push as commit a18beb4.
Since your change was applied there have been 54 commits pushed to the master branch:

  • fdd9ca7: 8280642: ObjectInputStream.readObject should throw InvalidClassException instead of IllegalAccessError
  • d95de5c: 8255495: Support CDS Archived Heap for uncompressed oops
  • bde2b37: 8279954: java/lang/StringBuffer(StringBuilder)/HugeCapacity.java intermittently fails
  • d1cc5fd: 8280941: os::print_memory_mappings() prints segment preceeding the inclusion range
  • 4532c3a: 8280554: resourcehogs/serviceability/sa/ClhsdbRegionDetailsScanOopsForG1.java can fail if GC is triggered
  • 5080e81: 8280770: serviceability/sa/ClhsdbThreadContext.java sometimes fails with 'Thread "SteadyStateThread"' missing from stdout/stderr
  • 1f6fcbe: 8278475: G1 dirty card refinement by Java threads may get unnecessarily paused
  • c5a8612: 8280458: G1: Remove G1BlockOffsetTablePart::_next_offset_threshold
  • 86debf4: 8280932: G1: Rename HeapRegionRemSet::_code_roots accessors
  • d37fb1d: 8280870: Parallel: Simplify CLD roots claim in Full GC cycle
  • ... and 44 more: https://git.openjdk.java.net/jdk/compare/cab590517bf705418c7376edd5d7066b13b6dde8...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Feb 1, 2022
@openjdk openjdk bot closed this Feb 1, 2022
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Feb 1, 2022
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openjdk bot commented Feb 1, 2022

@shipilev Pushed as commit a18beb4.

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

@shipilev shipilev deleted the JDK-8280867-amd-flags branch March 7, 2022 10:59
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