Balloon: relax memory comparison thresholds for Windows guests

[elizashurov]

Increase guest_compare_threshold and guest_mem_ratio to reduce false failures caused by small differences between QEMU monitor and Windows guest reported memory after ballooning operations.

ID:4607

Summary by CodeRabbit

• Chores
  • Updated Windows guest memory management configuration parameters to enhance balloon service performance during testing scenarios.

[coderabbitai]

Walkthrough

The pull request updates two configuration parameters in the QEMU balloon service test file. The guest_compare_threshold value is increased from 300 to 700, and the guest_mem_ratio value is increased from 0.025 to 0.08. These are numerical adjustments to test configuration settings with no structural or logic changes to the configuration file.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

• Single file modified with only parameter value adjustments
• No logic, structural, or functional changes
• Configuration tuning only requires verification that new values are appropriate for test behavior

Pre-merge checks and finishing touches

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: increasing memory comparison thresholds for Windows balloon service testing to reduce false failures.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between a0379c1 and 6c17b3b.

📒 Files selected for processing (1)

• qemu/tests/cfg/balloon_service.cfg (1 hunks)

🔇 Additional comments (1)

qemu/tests/cfg/balloon_service.cfg (1)

13-14: Thresholds serve different purposes; confirm the new values won't mask legitimate failures.

The parameter changes are correctly isolated to balloon_service.cfg and serve distinct purposes:

• guest_compare_threshold and guest_mem_ratio (lines 13-14): Used in memory ballooning operation variance checks
• check_mem_diff (line 26): Used in separate QMP statistics validation—correctly unchanged

The balloon_service test uniquely performs service start/stop/restart operations alongside memory ballooning, which likely introduces additional Windows driver variance justifying higher tolerance thresholds.

However, the specific increases are substantial (700 MB threshold +133%, 8% ratio +220%), and there's no documented evidence (comments, test results, or configuration rationale) explaining why these particular values were chosen or validated through testing.

Recommendation: Verify that:

1. These thresholds were empirically tested to ensure they don't mask legitimate memory reporting failures
2. The values are specific to balloon_service operations (not needed for other balloon tests)
3. Thresholds remain appropriately constrained while addressing the false failure issue

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