8366082: Improve queue size computation in CPU-time sampler

[parttimenerd]

Improve the sample queue size computation for the CPU-time sampler by increasing the size dynamically when needed, but keeping the default size small.

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8366082: Improve queue size computation in CPU-time sampler (Enhancement - P4)

Reviewers

• Jaroslav Bachorik (@jbachorik - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/26926/head:pull/26926
$ git checkout pull/26926

Update a local copy of the PR:
$ git checkout pull/26926
$ git pull https://git.openjdk.org/jdk.git pull/26926/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 26926

View PR using the GUI difftool:
$ git pr show -t 26926

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/26926.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back jbechberger! 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]

@parttimenerd 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:

8366082: Improve queue size computation in CPU-time sampler

Reviewed-by: jbachorik

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 217 new commits pushed to the master branch:

• f51e442: 8367098: RISC-V: sync CPU features with related JVM flags for dependant ones
• cfb8093: 8364103: Convert existing sprintf-chains to stringStream
• e16c510: 8367231: [BACKOUT] JDK-8366363: MemBaseline accesses VMT without using lock
• ... and 214 more: https://git.openjdk.org/jdk/compare/45726a1f8b8f76586037867a32b82f8ab9b96937...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]

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

• hotspot-jfr

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

[mlbridge]

Webrevs

• 08: Full - Incremental (cab51632)
• 07: Full - Incremental (7e902494)
• 06: Full - Incremental (fa60329a)
• 05: Full - Incremental (d67261a7)
• 04: Full - Incremental (6bd7cd5c)
• 03: Full - Incremental (57dc56ca)
• 02: Full - Incremental (cf65d57e)
• 01: Full - Incremental (97669fe5)
• 00: Full (1c7b5b82)

[jbachorik]

NIT: This could be probably more efficient by bulding time quantized bucket

[parttimenerd]

Sure. But I'm only getting 10 or so events, so I didn't think it would be worth it

[jbachorik]

I have a few more minor questions/nits

[parttimenerd]

I'm looking forward to your nits :)

[parttimenerd]

/integrate

[openjdk]

Going to push as commit 002f936.
Since your change was applied there have been 218 commits pushed to the master branch:

• 4fc917c: 8366486: Test jdk/jfr/event/profiling/TestCPUTimeSampleMultipleRecordings.java is timing out
• f51e442: 8367098: RISC-V: sync CPU features with related JVM flags for dependant ones
• cfb8093: 8364103: Convert existing sprintf-chains to stringStream
• ... and 215 more: https://git.openjdk.org/jdk/compare/45726a1f8b8f76586037867a32b82f8ab9b96937...master

Your commit was automatically rebased without conflicts.

[openjdk]

@parttimenerd Pushed as commit 002f936.

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

[dholmes-ora]

The new test is failing in our CI. I will file a bug and assign it to you.

[parttimenerd]

/backport jdk25u-dev

[openjdk]

@parttimenerd the backport was successfully created on the branch backport-parttimenerd-002f936e-master in my personal fork of openjdk/jdk25u-dev. To create a pull request with this backport targeting openjdk/jdk25u-dev:master, just click the following link:

➡️ Create pull request

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 002f936e from the openjdk/jdk repository.

The commit being backported was authored by Johannes Bechberger on 9 Sep 2025 and was reviewed by Jaroslav Bachorik.

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-dev:

$ git fetch https://github.com/openjdk-bots/jdk25u-dev.git backport-parttimenerd-002f936e-master:backport-parttimenerd-002f936e-master
$ git checkout backport-parttimenerd-002f936e-master
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk25u-dev.git backport-parttimenerd-002f936e-master

⚠️ @parttimenerd You are not yet a collaborator in my fork openjdk-bots/jdk25u-dev. An invite will be sent out and you need to accept it before you can proceed.