[https://nvbugs/5422621][fix] fix EPLB init hang (cherry-pick #8649)

[syuoni]

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Summary by CodeRabbit

• Bug Fixes
  • Fixed expert token count initialization in load balancing operations to ensure proper zero-initialization across all scenarios.

[syuoni]

/bot run --disable-fail-fast

[coderabbitai]

📝 Walkthrough

Walkthrough

Removed an early exit condition in the zeroExpertTokenCountKernel CUDA kernel. Previously, the kernel would return without executing when enabled was 0. Now the kernel always executes and explicitly zero-initializes expert token counts per thread regardless of the enabled flag state.

Changes

Cohort / File(s)	Change Summary
CUDA kernel control flow modification cpp/tensorrt_llm/kernels/moeLoadBalance/moeLoadBalanceKernels.cu	Removed early exit condition in zeroExpertTokenCountKernel when enabled flag is 0; kernel now always executes and writes zeroed values for threadIdx.x, changing behavior from leaving memory unchanged to explicit zero-initialization of expert token counts

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Control flow change with potential side effects: Removal of the early exit may alter the kernel's behavior and memory access patterns in scenarios where enabled is 0, requiring verification that the new behavior is intentional and correct.
• Kernel execution semantics: Confirm that always executing the kernel body (including writes) aligns with the intended semantics and doesn't introduce unintended memory operations or race conditions.
• State initialization: Verify that explicit zero-initialization on each kernel invocation is the desired behavior and doesn't conflict with upstream or downstream logic.

Pre-merge checks and finishing touches

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description Check	⚠️ Warning	The pull request description is largely incomplete. The author has left the required template sections unfilled: the Description section contains only a placeholder comment with no explanation of the issue or solution, the Test Coverage section is similarly empty, and while the PR Checklist was acknowledged with a final checkbox, no substantive information was provided for any of the individual items. The description provides no technical context, implementation details, or test information beyond what can be inferred from the title and code diff.
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.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title Check	✅ Passed	The pull request title "[https://nvbugs/5422621][fix] fix EPLB init hang (cherry-pick #8649)" follows the prescribed template format with a valid NVBugs ID, appropriate type indicator ([fix]), and a clear summary. The title directly relates to the changeset, which removes an early exit condition in the zeroExpertTokenCountKernel to fix an initialization hang. The title is concise, specific, and clearly communicates the primary purpose of the change to readers reviewing the git history.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

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📜 Recent review details

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between b334102 and b10c1d9.

📒 Files selected for processing (1)

• cpp/tensorrt_llm/kernels/moeLoadBalance/moeLoadBalanceKernels.cu (0 hunks)

💤 Files with no reviewable changes (1)

• cpp/tensorrt_llm/kernels/moeLoadBalance/moeLoadBalanceKernels.cu

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[tensorrt-cicd]

PR_Github #22768 [ run ] triggered by Bot. Commit: b10c1d9

[tensorrt-cicd]

PR_Github #22768 [ run ] completed with state SUCCESS. Commit: b10c1d9
/LLM/release-1.1/L0_MergeRequest_PR pipeline #291 completed with status: 'FAILURE'

[syuoni]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #22815 [ run ] triggered by Bot. Commit: b78407e

[tensorrt-cicd]

PR_Github #22815 [ run ] completed with state SUCCESS. Commit: b78407e
/LLM/release-1.1/L0_MergeRequest_PR pipeline #294 completed with status: 'FAILURE'

[syuoni]

/bot run

[tensorrt-cicd]

PR_Github #22857 [ run ] triggered by Bot. Commit: b78407e

[tensorrt-cicd]

PR_Github #22857 [ run ] completed with state SUCCESS. Commit: b78407e
/LLM/release-1.1/L0_MergeRequest_PR pipeline #301 completed with status: 'FAILURE'

[syuoni]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #22889 [ run ] triggered by Bot. Commit: b78407e

[tensorrt-cicd]

PR_Github #22889 [ run ] completed with state SUCCESS. Commit: b78407e
/LLM/release-1.1/L0_MergeRequest_PR pipeline #305 completed with status: 'SUCCESS'