[Bugfix][DeepSeek V4] Forward input IDs across pipeline stages

[ZacharyZcR]

Purpose

DeepSeek V4 MegaMoE routing consumes the original token IDs in every decoder layer. Under pipeline parallelism, the V2 runner only supplies input_ids to the first pipeline rank, while later ranks receive None plus the intermediate tensor payload. As a result, TP2 x PP3 serving fails when a non-first pipeline stage tries to use the missing IDs.

This change carries input_ids alongside hidden_states in the DeepSeek V4 pipeline intermediate tensors. It preserves the integer dtype required by MegaMoE and keeps existing auxiliary hidden-state payloads intact.

Duplicate searches were performed for DeepSeek V4 pipeline-parallel input_ids issues and PRs; no matching fix was found.

Test Plan

• Verify the intermediate tensor factory allocates input_ids with the expected shape and torch.int64 dtype.
• Launch DeepSeek-V4-Flash-Vision-Exp on six RTX 5090 GPUs with tensor parallel size 2 and pipeline parallel size 3.
• Send one text chat completion and one local-image chat completion.
• Confirm both requests terminate normally rather than failing on a non-first pipeline rank.

Test Result

• git diff --check: passed.
• Focused regression test added: test_deepseek_v4_pp_intermediate_tensors_include_input_ids.
• Real serving configuration: vLLM V2, TP=2, PP=3, FP8 KV cache, max model length 8192.
• Health endpoint became ready across all six workers.
• Text request completed with finish_reason=stop and returned PP_TEXT_OK.
• Vision request using inference/examples/images/corn.jpeg completed with finish_reason=stop and returned 玉米.
• Before the fix, non-first pipeline stages received no token IDs. With the fix, all three pipeline stages completed sparse-MLA warmup and end-to-end generation.

AI assistance disclosure

AI assistance was used to investigate the failure, prepare the patch, and draft this description. The submitter reviewed every changed line and the test evidence before submission.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Team

Run ID: 88b73e6f-c9f1-41b2-9fdb-e951053ad250

📥 Commits

Reviewing files that changed from the base of the PR and between f4eccda and 37e6f27.

📒 Files selected for processing (2)

• tests/models/test_deepseek_v4_mega_moe.py
• vllm/models/deepseek_v4/nvidia/model.py

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Improved DeepSeek V4 pipeline-parallel execution by preserving input token IDs across processing stages.
  • Ensured downstream hash-based mixture-of-experts and vision routing receive the required input tokens.

• Tests

  • Added coverage verifying that intermediate pipeline data includes correctly shaped, 64-bit input ID tensors.

Walkthrough

DeepSeek V4 now carries input_ids through pipeline-parallel intermediate tensors. Non-first stages restore the IDs, and non-last stages forward them. Tests verify the buffer shape and dtype.

Changes

DeepSeek V4 pipeline propagation

Layer / File(s)	Summary
Intermediate tensor contract vllm/models/deepseek_v4/nvidia/model.py, tests/models/test_deepseek_v4_mega_moe.py	make_empty_intermediate_tensors adds an int64 input_ids buffer. Tests verify its shape and dtype.
Pipeline forward propagation vllm/models/deepseek_v4/nvidia/model.py	forward restores input_ids on non-first pipeline ranks and forwards them with hidden_states to later stages.

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

Merge Risk: ⚪ Minimal · up to 37e6f

DeepSeek V4 pipeline stages now retain input token IDs required for MegaMoE routing, with coverage for the intermediate tensor contract. No current merge-blocking risk is identified.

Suggested reviewers: hollowman6

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the DeepSeek V4 bug fix and the forwarding of input IDs across pipeline stages.
Description check	✅ Passed	The description directly explains the pipeline-parallel failure, the input_ids fix, and the validation results.
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.

• 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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