cgmon: fix the issue that CPU quota is 0 if it's not limited by cgroup

[YangKeao]

What problem does this PR solve?

Issue Number: close #61223

Problem Summary:

The cpu quota will always be 0 if it failed to get the cgroup limit. The same issue also exists for memory.

What changed and how does it work?

Change the logic of error handling in cgmon. Make the cpu quota defaults to the count of CPU, and the memory quota defaults to the memory get from /proc/meminfo. Then update these values according to the cgroup settings.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

1. Deploy master branch of tidb in rockylinux 9. Open the grafana. The cpu quota is 0.

2. Deploy this branch of TiDB in rockylinux 9. Open the grafana. The cpu quota is 16.

3. Modify the tiup config of TiDB. Set CPU quota to 800 and memory quota to 8G. The value is correct.

4. Manually remove the memory controller from related cgroup, so that TiDB will get error when it's reading the memory quota, then the memory quota goes to the memory of the whole machine (16G).

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Fix the issue that the cpu quota is always 0 if `cpu.max` doesn't exist

[YangKeao]

Ref #50468

[YangKeao]

This variable is not used. I don't know why it was here before.

[YangKeao]

Just a rename. Because it's actually not GOMAXPROCS, it's NumCPU.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.6258%. Comparing base (3ab8c7f) to head (348dad8).
Report is 7 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #61322        +/-   ##
================================================
+ Coverage   73.1942%   73.6258%   +0.4315%     
================================================
  Files          1726       1726                
  Lines        478576     479082       +506     
================================================
+ Hits         350290     352728      +2438     
+ Misses       106833     104949      -1884     
+ Partials      21453      21405        -48     

Flag	Coverage Δ
integration	42.5659% <100.0000%> (?)
unit	72.5047% <81.2500%> (+0.0292%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.7804% <ø> (ø)
parser	∅ <ø> (∅)
br	47.5567% <ø> (-0.0164%)	⬇️

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[YangKeao]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, hawkingrei

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-05-27 05:19:36.736676938 +0000 UTC m=+332707.108464387: ☑️ agreed by hawkingrei.
• 2025-05-27 05:45:27.1218382 +0000 UTC m=+334257.493625658: ☑️ agreed by Defined2014.