[#2338][fix] Fix missing encoder outputs when return_encoder_output=True

[crendelyok]

Summary by CodeRabbit

• Bug Fixes
  • Fixed encoder output synchronization in distributed pipeline parallel execution, ensuring proper output transfer across pipeline ranks during batch processing.

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Description

Fixing encoder outputs are always zero when using return_encoder_output=True in the OutputConfig
#2338

I noticed that TrtEncoderModel::executeBatch(RequestVector const& requestList) does implement the correct logic for copying encoder outputs, but not TrtEncoderModel::executeBatch(ScheduledRequests const& scheduledRequests) which is actually used in forwardAsync.
I also noticed that there is TrtEncoderModel::forwardSync() which is 1) uses TrtEncoderModel::executeBatch(RequestVector const& requestList) 2) never used anywhere except tests. Probably some clarifications from NVIDIA team would be useful.

Test Coverage

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[coderabbitai]

📝 Walkthrough

Walkthrough

The code now conditionally synchronizes encoder outputs after engine execution in TrtEncoderModel::executeBatch based on pipeline parallel rank: if it is the last pipeline rank, fillEncoderOutputSync transfers outputs to requests; otherwise, the buffer stream is synchronized.

Changes

Cohort / File(s)	Summary
Post-execution synchronization logic cpp/tensorrt_llm/batch_manager/trtEncoderModel.cpp	Added conditional rank-aware synchronization after engine execution: calls fillEncoderOutputSync for last pipeline parallel rank, synchronizes stream for other ranks

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Verify the pipeline parallel rank check condition is correct
• Confirm fillEncoderOutputSync semantics and behavior for the last PP rank
• Ensure stream synchronization for non-last ranks is appropriate

Pre-merge checks and finishing touches

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.
Description check	❓ Inconclusive	PR description identifies the issue (GitHub #2338) and explains the root cause, but Test Coverage section is empty and critical checklist items lack clear verification.	Add specific test cases that verify encoder outputs are correctly returned when return_encoder_output=True, and confirm all checklist items are addressed before merge.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the fix for a specific issue (missing encoder outputs) with a concrete condition (return_encoder_output=True) and includes the GitHub issue reference (#2338).

✨ Finishing touches

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[karljang]

/bot run

[tensorrt-cicd]

PR_Github #27538 [ run ] triggered by Bot. Commit: a024545

[tensorrt-cicd]

PR_Github #27538 [ run ] completed with state FAILURE. Commit: a024545
LLM/main/L0_MergeRequest_PR #21017 (Blue Ocean) completed with status: ABORTED

[karljang]

/bot run

[tensorrt-cicd]

PR_Github #27604 [ run ] triggered by Bot. Commit: a024545

[karljang]

/bot run

[tensorrt-cicd]

PR_Github #27759 [ run ] triggered by Bot. Commit: a024545

[karljang]

@kaiyux , Could you please review or assign this PR? CI is still failing, but the errors don’t seem to be related to this PR.

[tensorrt-cicd]

PR_Github #27759 [ run ] completed with state SUCCESS. Commit: a024545
/LLM/main/L0_MergeRequest_PR pipeline #21186 completed with status: 'SUCCESS'

[MahmoudAshraf97]

Thanks @crendelyok , @karljang I currently do not have the capacity to test this but LGTM

[karljang]

@kaiyux , could you please review this PR~ thank you!

[crendelyok]

hello, any updates?