resource_group client: prevent NaN in calcAvg when elapsed duration is zero

[JmPotato]

What problem does this PR solve?

Issue Number: Close #11022, ref #9455

What is changed and how does it work?

A freshly created `groupCostController` can be published to the controller
map between the `updateRunState` and `updateAvgRequestResourcePerSec` passes
of the same tick. In that case `gc.run.now` still equals the `avgLastTime`
set by `initRunState` (the same `time.Now()` value), so `calcAvg` computes
`(0-0)/0 = NaN`, permanently poisoning `avgRUPerSec` (the moving average
keeps NaN forever) and making every subsequent token-bucket request carry
`required-token=NaN` until the idle cleanup deletes the controller.

Skip the sample when the elapsed duration is non-positive, and update the
`burstable` flag before sampling so a skipped sample does not delay it.
A regression test reproduces the exact scenario and verifies `avgRUPerSec`
stays finite and sampling resumes once the run state advances.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

Fix the issue that the resource group client might permanently send `NaN` token requests when a newly created resource group controller races with the periodic state update.

Summary by CodeRabbit

• Bug Fixes

  • Improved request-rate tracking when no time has elapsed between measurements.
  • Prevented invalid rate values from affecting resource usage calculations.
  • Ensured burst handling state is updated consistently during request-rate updates.

• Tests

  • Added coverage for skipped measurements and resumed tracking after time advances.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 705c4787-590e-4520-83e5-74680eb01bd5

📥 Commits

Reviewing files that changed from the base of the PR and between 0b37df9 and f2bcfc2.

📒 Files selected for processing (2)

• client/resource_group/controller/group_controller.go
• client/resource_group/controller/group_controller_test.go

---

📝 Walkthrough

Walkthrough

The resource group controller now records burstability before average calculation and skips RU-per-second sampling when runtime time has not advanced. A regression test verifies no NaN is produced, accounting state remains unchanged, and sampling resumes after time advances.

Changes

Resource average sampling

Layer / File(s)	Summary
Average sampling guard and regression coverage client/resource_group/controller/group_controller.go, client/resource_group/controller/group_controller_test.go	The controller updates burstability before calculating averages and returns early for non-positive durations. Tests verify preserved state, non-NaN output, and resumed sampling after a later tick.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested labels: type/development

Suggested reviewers: yuhaozhang00

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main fix: preventing NaN in calcAvg when elapsed duration is zero.
Description check	✅ Passed	The description includes the issue number, change summary, unit test, related changes, and release note as required.
Linked Issues check	✅ Passed	The changes address #11022 by guarding non-positive delta durations, preventing NaN, and adding a regression test for the race.
Out of Scope Changes check	✅ Passed	The patch stays focused on the race fix and its regression test, with no明显 unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[JmPotato]

/retest

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.25%. Comparing base (0b37df9) to head (f2bcfc2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11023      +/-   ##
==========================================
+ Coverage   79.23%   79.25%   +0.01%     
==========================================
  Files         541      541              
  Lines       76035    76037       +2     
==========================================
+ Hits        60245    60261      +16     
+ Misses      11545    11523      -22     
- Partials     4245     4253       +8     

Flag	Coverage Δ
unittests	79.25% <100.00%> (+0.01%)	⬆️

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-07-20 05:57:05.356377199 +0000 UTC m=+1211611.392472254: ☑️ agreed by lhy1024.
• 2026-07-20 06:08:10.204419066 +0000 UTC m=+1212276.240514122: ☑️ agreed by bufferflies.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bufferflies, lhy1024, rleungx, YuhaoZhang00

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Needs approval from an approver in each of these files:

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[JmPotato]

/retest

[JmPotato]

/test pull-unit-test-next-gen-3

[JmPotato]

/test pull-unit-test-next-gen-3

[JmPotato]

/test pull-unit-test-next-gen-3

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #11028.