[Bugfix][Multimodal] Bound renderer warmup to the prefill token budget

[lucamotz]

Purpose

Long-context multimodal renderer warmup retains unnecessary CPU memory. Let MultiModalRegistry.get_dummy_mm_inputs derive the warmup budget from the renderer's scheduler config, capped by max_num_batched_tokens only with chunked prefill enabled. Existing profiling callers retain full-context inputs.

Replaces the renderer fix in #55435. Duplicate check: no other open PR found for this warmup budget. AI-assisted contribution.

Test Plan

.venv/bin/python -m pytest tests/renderers/test_warmup.py tests/multimodal/test_registry.py -k 'not supports_multimodal_inputs' -q --tb=short

Test Result

31 passed, 4 unrelated model-config tests deselected. Changed-file pre-commit hooks passed.

Earlier combined-fix GLM-5.3-Flash TP2 validation passed vision checks and 50k/480k/262k-token prompts.

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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• The test results, such as pasting the results comparison before and after, or e2e results
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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Team

Run ID: cf9c598a-0da9-4e28-a252-70a3bf23aea2

📥 Commits

Reviewing files that changed from the base of the PR and between 1e4f842 and bb43d3a.

📒 Files selected for processing (4)

• tests/multimodal/test_registry.py
• tests/renderers/test_warmup.py
• vllm/multimodal/registry.py
• vllm/renderers/base.py

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Improved multimodal warmup sequence-length selection based on the configured scheduler budget when chunked prefill is enabled.
  • Ensured warmup uses the model’s maximum context length when no lower scheduler limit applies.
  • Preserved full-context dummy inputs for profiling while respecting configured token budgets.

• Tests

  • Updated coverage for scheduler-budget limits and model-length boundaries.
  • Simplified warmup validation to focus on expected sequence lengths across supported configurations.

Walkthrough

Multimodal warmup now delegates dummy-input sequence-length selection to the registry. The registry uses model and scheduler limits, including chunked-prefill limits. Tests cover scheduler budgets and bounded warmup lengths.

Changes

Multimodal warmup bounding

Layer / File(s)	Summary
Registry scheduler budget and validation vllm/multimodal/registry.py, tests/multimodal/test_registry.py	get_dummy_mm_inputs accepts scheduler_config, defaults to max_model_len, and applies max_num_batched_tokens when chunked prefill is enabled. Tests verify the selected sequence length and prompt-token count.
Renderer warmup integration and coverage vllm/renderers/base.py, tests/renderers/test_warmup.py	_warmup_mm_processor passes scheduler configuration to get_dummy_mm_inputs. Tests verify sequence lengths of 8192 and 128 for the configured model lengths.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to bb43d

Multimodal warmup now limits long-context dummy inputs to the scheduler budget when chunked prefill is enabled, reducing retained CPU memory while preserving smaller model context limits. The bounded behavior is covered at the renderer boundary, with no current merge-blocking risk identified.

Suggested reviewers: darklight1337

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The description clearly explains the multimodal renderer warmup budget change, its purpose, implementation, and validation results.
Title check	✅ Passed	The title clearly and concisely identifies the bugfix: bounding multimodal renderer warmup by the prefill token budget.

• Fix all pre-merge checks with AI

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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[github-actions]

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[claude]

Claude Code Review

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[lucamotz]

/ci run

[github-actions]

✅ Triggered Buildkite CI #87400 for commit bb43d3a8674c.

[lucamotz]

@DarkLight1337 CI passed. I think it’s not automerging because of the previously failed pre commit check? I don’t think I have the permissions to rerun that. If I do, sorry for pinging you again and please let me know.
Thanks for the quick review and also the good feedback!

[DarkLight1337]

Retrying