8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present #27320

vamsi-parasa · 2025-09-16T18:04:33Z

The goal of this PR is to enable APX on Intel CPUs (i.e. enable UseAPX) only when both the APX_F and APX_NCI_NDD_NF cpuid feature flags are present.

The latest update to the Intel APX specification (https://www.intel.com/content/www/us/en/content-details/861610/intel-advanced-performance-extensions-intel-apx-architecture-specification.html ) has changed how APX features are detected on Intel CPUs. Because of this change, we need to update how the JVM enumerates CPU features.

As per the new update, when APX_F is set, processors also provide CPUID leaf 0x29 (APX Advanced Performance Extensions Leaf). Any Intel processor that enumerates APX_F also enumerates APX_NCI_NDD_NF.

This PR enhances the HotSpot x86 CPU feature detection to recognize the APX_NCI_NDD_NF sub-feature of Intel APX and update the enabling logic for UseAPX VM flag.

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Issue

JDK-8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present (Sub-task - P3)

Reviewers

Sandhya Viswanathan (@sviswa7 - Reviewer)
Volodymyr Paprotski (@vpaprotsk - Committer)

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$ git pull https://git.openjdk.org/jdk.git pull/27320/head

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…_NDD_NF cpuid features are present

bridgekeeper · 2025-09-16T18:05:48Z

👋 Welcome back sparasa! 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 · 2025-09-16T18:07:47Z

@vamsi-parasa 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:

8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present

Reviewed-by: sviswanathan, vpaprotski

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 67 new commits pushed to the master branch:

695e36b: 8367927: Remove 8043571-related tests from problemlists
16458b6: 8367725: Incorrect reading of oop in SuspendResumeManager::suspend while thread is blocked
1512d88: 8348278: Trim InitialRAMPercentage to improve startup in default modes
... and 64 more: https://git.openjdk.org/jdk/compare/e883dec6be8cb2fc44e45a6b4677cca2f4df58ef...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 · 2025-09-16T18:08:28Z

@vamsi-parasa The following labels will be automatically applied to this pull request:

graal
hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-09-16T18:12:35Z

Webrevs

sviswa7 · 2025-09-17T00:26:32Z

src/hotspot/cpu/x86/vm_version_x86.cpp


  if (!UseAPX) {
    _features.clear_feature(CPU_APX_F);
+    _features.clear_feature(CPU_APX_NCI_NDD_NF);


We don't need separate CPU_APX_NCI_NDD_NF feature and the related changes as CPU_APX_F feature is set only when both bits (sefsl1_cpuid7_edx.bits.apx_f and std_cpuid29_ebx.bits.apx_nci_ndd_nf) are set.

Please see the updated changes which removes CPU_APX_NCI_NDD_NF as an explicit feature.

sviswa7

Looks good to me.

vpaprotsk

Thanks for answering my questions.. things we checked:

double-checked reg parameter values of cpuid against the spec
double-checked endianness of bitset variables in C grammar
double-checked how offset to the field std_cpuid29_ebx is computed

Change looks good to me

vpaprotsk · 2025-09-18T20:59:30Z

src/hotspot/cpu/x86/vm_version_x86.cpp

  if (sefsl1_cpuid7_edx.bits.apx_f != 0 &&
-      xem_xcr0_eax.bits.apx_f != 0) {
+      xem_xcr0_eax.bits.apx_f != 0 &&
+      std_cpuid29_ebx.bits.apx_nci_ndd_nf != 0) {


was confused why the previous implementation was 'wrong'.. Please clarify that this was triggered "because" of the update to the spec (in the PR description).

Please see the updated PR description which clarifies that this PR was triggered because of the update to the Intel APX spec.

vamsi-parasa · 2025-09-19T16:24:44Z

Change looks good to me

Thanks Vlad for going through the changes and reviewing the PR!

vamsi-parasa · 2025-09-19T18:17:36Z

/integrate

openjdk · 2025-09-19T18:18:55Z

Going to push as commit 3d4e049.
Since your change was applied there have been 68 commits pushed to the master branch:

bca1e6e: 8365626: (fs) Improve handling of broken links in Files.isSameFile() (win)
695e36b: 8367927: Remove 8043571-related tests from problemlists
16458b6: 8367725: Incorrect reading of oop in SuspendResumeManager::suspend while thread is blocked
... and 65 more: https://git.openjdk.org/jdk/compare/e883dec6be8cb2fc44e45a6b4677cca2f4df58ef...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-09-19T18:19:04Z

@vamsi-parasa Pushed as commit 3d4e049.

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

jatin-bhateja · 2025-09-23T10:23:35Z

/label add hotspot-compiler-dev

openjdk · 2025-09-23T10:24:41Z

@jatin-bhateja The command label can only be used in open pull requests.

jatin-bhateja · 2025-09-23T10:37:53Z

Hi @vamsi-parasa ,

Before this PR, we could validate APX support using the publicly available latest version 9.58 of Intel software development emulator.

EMR>sde64 --version
Intel(R) Software Development Emulator.  Version:  9.58.0 external (0)
Copyright (C) 2008-2025, Intel Corporation. All rights reserved.

EMR>sde64 -dmr -ptr_raise -- java -XX:+PrintFlagsFinal -XX:+UnlockExperimentalVMOptions -XX:+UseAPX --version | grep APX
     bool UseAPX                                   = true                            {ARCH experimental} {command line}

After this PR, UseAPX support is false. I think we should delay upstreaming any new feature support until SDE rolls out the support.

EMR>sde64 -dmr -ptr_raise -- java -XX:+PrintFlagsFinal -XX:+UnlockExperimentalVMOptions -XX:+UseAPX --version | grep APX
OpenJDK 64-Bit Server VM warning: UseAPX is not supported on this CPU, setting it to false
     bool UseAPX                                   = false                           {ARCH experimental} {command line}

Best Regards,
Jatin

vamsi-parasa · 2025-09-25T00:45:37Z

EMR>sde64 -dmr -ptr_raise -- java -XX:+PrintFlagsFinal -XX:+UnlockExperimentalVMOptions -XX:+UseAPX --version | grep APX
OpenJDK 64-Bit Server VM warning: UseAPX is not supported on this CPU, setting it to false

Hi Jatin,

Thank for informing about this issue!
Sorry about the SDE issue. Will inform you once the public version of SDE which supports this feature is avalible.

Thanks,
Vamsi

jatin-bhateja · 2025-09-25T17:45:28Z

EMR>sde64 -dmr -ptr_raise -- java -XX:+PrintFlagsFinal -XX:+UnlockExperimentalVMOptions -XX:+UseAPX --version | grep APX
OpenJDK 64-Bit Server VM warning: UseAPX is not supported on this CPU, setting it to false

Hi Jatin,

Thank for informing about this issue! Sorry about the SDE issue. Will inform you once the public version of SDE which supports this feature is avalible.

Thanks, Vamsi

Thanks @vamsi-parasa, BTW, there should not be any urgency to push a patch for future enhancement in the absence of software emulation :-)

vamsi-parasa · 2025-10-02T18:03:16Z

/backport openjdk/jdk25u

openjdk · 2025-10-02T18:06:54Z

@vamsi-parasa the backport was successfully created on the branch backport-vamsi-parasa-3d4e0491-master in my personal fork of openjdk/jdk25u. To create a pull request with this backport targeting openjdk/jdk25u:master, just click the following link:

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The title of the pull request is automatically filled in correctly and below you find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit 3d4e0491 from the openjdk/jdk repository.

The commit being backported was authored by Srinivas Vamsi Parasa on 19 Sep 2025 and was reviewed by Sandhya Viswanathan and Volodymyr Paprotski.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk25u:

$ git fetch https://github.com/openjdk-bots/jdk25u.git backport-vamsi-parasa-3d4e0491-master:backport-vamsi-parasa-3d4e0491-master
$ git checkout backport-vamsi-parasa-3d4e0491-master
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk25u.git backport-vamsi-parasa-3d4e0491-master

vamsi-parasa added 2 commits September 16, 2025 10:30

8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI…

ea1946d

…_NDD_NF cpuid features are present

clean up

4072cfb

openjdk bot added graal graal-dev@openjdk.org hotspot hotspot-dev@openjdk.org rfr Pull request is ready for review labels Sep 16, 2025

vamsi-parasa added 3 commits September 16, 2025 11:48

merge master

4bf728c

integrate latest changes

87e96cc

update KNL check

21560d0

sviswa7 reviewed Sep 17, 2025

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vamsi-parasa added 2 commits September 17, 2025 10:48

Remove APX_NCI_NDD_NF as an explicit feature

4e7a183

Update CPUInfoTest.java

91f589a

sviswa7 approved these changes Sep 18, 2025

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vpaprotsk approved these changes Sep 18, 2025

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openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 19, 2025

jatin-bhateja mentioned this pull request Oct 21, 2025

8351016: RA support for EVEX to REX/REX2 demotion to optimize NDD instructions #26283

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8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present #27320

8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present #27320

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