[TRTLLM-10030][perf] avoid sync in PyTorchModelEngine when using beam search

[ixlmar]

Description

see PR title

Test Coverage

Might want to add tests using assert_no_cuda_sync at some point.

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Summary by CodeRabbit

• Performance
  • Optimized GPU memory transfer operations to improve inference efficiency and reduce latency during model execution.

[ixlmar]

/bot run --disable-fail-fast

[coderabbitai]

📝 Walkthrough

Walkthrough

Modified tensor creation in previous_seq_slots_device to use pinned memory with non-blocking transfer to CUDA device instead of direct CUDA tensor construction. This is a performance optimization enabling potential overlap of host-to-device transfers while avoiding implicit synchronization.

Changes

Cohort / File(s)	Summary
Tensor Creation Optimization tensorrt_llm/_torch/pyexecutor/model_engine.py	Changed gen_request_seq_slots_tensor construction from direct CUDA device creation to pinned memory allocation followed by non-blocking transfer to CUDA, enabling overlapped transfers and reducing synchronization overhead.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is minimal and defers to the PR title, with only a brief note on future testing improvements. Required sections like detailed description and test coverage details are largely incomplete.	Expand the description to explain what change avoids the sync, why it matters, and what testing has been done. Provide more concrete details about the implementation and its impact.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Title check	✅ Passed	The title accurately describes the main change: avoiding CUDA synchronization in PyTorchModelEngine when using beam search by using pinned memory and non-blocking transfers.

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[tensorrt-cicd]

PR_Github #35086 [ run ] triggered by Bot. Commit: 7d0277a

[ixlmar]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35109 [ run ] triggered by Bot. Commit: 15087b5

[ixlmar]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35140 [ run ] triggered by Bot. Commit: 15087b5

[tensorrt-cicd]

PR_Github #35109 [ run ] completed with state ABORTED. Commit: 15087b5
LLM/main/L0_MergeRequest_PR #27102 (Blue Ocean) completed with status: ABORTED

[tensorrt-cicd]

PR_Github #35140 [ run ] completed with state SUCCESS. Commit: 15087b5
/LLM/main/L0_MergeRequest_PR pipeline #27131 completed with status: 'FAILURE'

⚠️ Action Required:

• Please check the failed tests and fix your PR
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• Once fixed, request an NVIDIA team member to trigger CI again

[brb-nv]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35161 [ run ] triggered by Bot. Commit: 15087b5

[tensorrt-cicd]

PR_Github #35161 [ run ] completed with state SUCCESS. Commit: 15087b5
/LLM/main/L0_MergeRequest_PR pipeline #27152 completed with status: 'FAILURE'

⚠️ Action Required:

• Please check the failed tests and fix your PR
• If you cannot view the failures, ask the CI triggerer to share details
• Once fixed, request an NVIDIA team member to trigger CI again

[yuxianq]

/bot skip --comment "the failed tests are unrelated to this PR, skip CI to unblock main branch"

[tensorrt-cicd]

PR_Github #35170 [ skip ] triggered by Bot. Commit: 15087b5

[tensorrt-cicd]

PR_Github #35170 [ skip ] completed with state SUCCESS. Commit: 15087b5
Skipping testing for commit 15087b5