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@nv-yilinf nv-yilinf commented Jul 31, 2025

Summary by CodeRabbit

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  • Refactor
    • Improved internal workspace management for better efficiency and reduced unnecessary memory allocations. No changes to user-facing features or functionality.

Description

In current MoE runner implementation, the runner will allocate a new workspace Tensor each time invoking the kernel. Even though backed by torch's caching allocator, frequent cudaMalloc/Frees are usually considered not a good practice and sometimes causes cudaMalloc to take ~100ms.
In this PR we fix this issue by maintaining the workspace tensor as a Class variable and only reallocates when target size is larger than current size or when capturing cuda graph.

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📝 Walkthrough

Walkthrough

The code refactors workspace management in the FusedMoeRunner class by replacing the getWorkspaceInfo method with a new setWorkspaceInfo method. Workspace allocation is now handled in-place via a member variable, reducing unnecessary allocations and centralizing state management. Related method calls and variable types are updated accordingly.

Changes

Cohort / File(s) Change Summary
Workspace Management Refactor
cpp/tensorrt_llm/thop/moeOp.cpp
Replaced getWorkspaceInfo with setWorkspaceInfo for in-place workspace updates; added workspace_info member; updated method calls and variable types for consistency.

Sequence Diagram(s)

sequenceDiagram
    participant Caller
    participant FusedMoeRunner

    Caller->>FusedMoeRunner: setWorkspaceInfo(params)
    alt workspace tensor large enough
        FusedMoeRunner->>FusedMoeRunner: Update src_to_dest_map pointer
    else workspace tensor too small
        FusedMoeRunner->>FusedMoeRunner: Log warning
        FusedMoeRunner->>FusedMoeRunner: Allocate new workspace tensor
        FusedMoeRunner->>FusedMoeRunner: Update src_to_dest_map pointer
    end
    Caller->>FusedMoeRunner: Use workspace_info member for further operations
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@nv-yilinf nv-yilinf requested a review from kaiyux July 31, 2025 04:55
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Actionable comments posted: 1

🧹 Nitpick comments (1)
cpp/tensorrt_llm/thop/moeOp.cpp (1)

580-580: Follow member variable naming convention.

The member variable workspace_info should be prefixed with 'm' according to the coding guidelines: mWorkspaceInfo.

-    WorkspaceInfo workspace_info;
+    WorkspaceInfo mWorkspaceInfo;

Note: This change would require updating all references to this variable throughout the class.

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  • cpp/tensorrt_llm/thop/moeOp.cpp (5 hunks)
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**/*.{cpp,h,hpp,cc,cxx}

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🔇 Additional comments (3)
cpp/tensorrt_llm/thop/moeOp.cpp (3)

311-312: LGTM! Workspace allocation optimization implemented correctly.

The calls to setWorkspaceInfo properly replace the previous getWorkspaceInfo pattern, supporting the PR objective of reducing frequent memory allocations. Both calling methods are already protected by mutex locks, ensuring thread safety.

Also applies to: 442-443


626-647: Excellent optimization approach with minor implementation improvements needed.

The setWorkspaceInfo method successfully implements the PR objective of reducing frequent memory allocations by maintaining workspace as a member variable and only reallocating when necessary. This should significantly improve performance by avoiding the costly cudaMalloc/cudaFree operations mentioned in the PR description.

The core logic is sound and the approach is well-designed for the use case.


637-637: Assignment to int64_t is correct.

Verified that common::calculateTotalWorkspaceSize returns size_t. Converting its result into a signed 64-bit integer aligns with our coding guideline to prefer signed types and removes the signed/unsigned mismatch when comparing against workspace.numel() (which returns int64_t). No changes are required here.

@nv-yilinf nv-yilinf changed the title [5412562](https://nvbugspro.nvidia.com/bug/5412562) Allocate MoE workspace only when necessary [https://nvbugspro.nvidia.com/bug/5412562] Allocate MoE workspace only when necessary Jul 31, 2025
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@nv-yilinf nv-yilinf requested a review from hlu1 August 1, 2025 00:12
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@nv-yilinf nv-yilinf changed the title [https://nvbugspro.nvidia.com/bug/5412562] Allocate MoE workspace only when necessary [https://nvbugs/5412562] Allocate MoE workspace only when necessary Aug 5, 2025
@nv-yilinf nv-yilinf changed the title [https://nvbugs/5412562] Allocate MoE workspace only when necessary [https://nvbugs/5412562][feat] Allocate MoE workspace only when necessary Aug 5, 2025
@nv-yilinf nv-yilinf force-pushed the fix-moe-workspace-allocation branch from a7ea695 to 02dcf16 Compare August 5, 2025 16:31
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nv-yilinf commented Aug 15, 2025

Close this PR because of the branch retarget mess. Created a replica targeting release/1.0 #6955

@nv-yilinf nv-yilinf closed this Aug 15, 2025
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