[None][fix] Fix the bug for top_k=10 in NVLinkOneSided AlltoAll. - #10197
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Signed-off-by: Bo Li <22713281+bobboli@users.noreply.github.com>
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📝 WalkthroughWalkthroughThese changes modify the MoE All-to-All kernel to restructure TOP_K conditional logic from mutually inclusive to mutually exclusive paths, and add test coverage for the top_k=10 scenario in dispatch and combine operations. Changes
Estimated code review effort🎯 2 (Simple) | ⏱️ ~10 minutes
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🧹 Nitpick comments (1)
tests/unittest/_torch/multi_gpu/test_moe_a2a.py (1)
567-567: Consider adding top_k=10 test coverage totest_dispatchas well.While this adds test coverage for the top_k=10 combine path, the
test_dispatchmethod (lines 478-496) lacks a corresponding top_k=10 test case. For symmetric coverage of the bug fix, consider adding a top_k=10 parameter totest_dispatchto ensure both dispatch and combine paths are validated for this configuration.Suggested test case addition
Add to the
@pytest.mark.parametrizedecorator fortest_dispatch(around line 479):(4, [32, 32, 32, 32], 10), # (top_k=10 is used by Qwen3-next)
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cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cutests/unittest/_torch/multi_gpu/test_moe_a2a.py
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📓 Path-based instructions (3)
**/*.py
📄 CodeRabbit inference engine (CODING_GUIDELINES.md)
**/*.py: Code developed for TensorRT-LLM should conform to Python 3.8+
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Python files should use snake_case naming:some_file.py
Python classes should use PascalCase naming:class SomeClass
Python functions and methods should use snake_case naming:def my_awesome_function():
Python local variables should use snake_case naming:my_variable = ...
Python variable names that start with a number should be prefixed with 'k':k_99th_percentile = ...
Python global variables should use upper snake_case with prefix 'G':G_MY_GLOBAL = ...
Python constants should use upper snake_case naming:MY_CONSTANT = ...
Avoid shadowing variables declared in an outer scope in Python
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When using try-except blocks in Python to handle multiple possible variable types (duck-typing), keep the body of the try as small as possible, using the else block for logic
Files:
tests/unittest/_torch/multi_gpu/test_moe_a2a.py
**/*.{cpp,h,cu,cuh,py}
📄 CodeRabbit inference engine (CODING_GUIDELINES.md)
All TensorRT-LLM Open Source Software code should contain an NVIDIA copyright header that includes the year of its latest meaningful modification
Files:
tests/unittest/_torch/multi_gpu/test_moe_a2a.pycpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
**/*.{cpp,h,cu,cuh}
📄 CodeRabbit inference engine (CODING_GUIDELINES.md)
**/*.{cpp,h,cu,cuh}: Closing braces of namespaces should have a comment saying the namespace it closes:} // namespace foo
Preferconstorconstexprvariables over#definewhenever possible, as the latter are not visible to the compiler
A variable that is not modified after its initialization should be declared asconst
For naming of constants in C++, follow the naming section conventions
Except0(only used in comparison for checking signness/existence/emptiness) andnullptr,true,false, all other literals should only be used for variable initialization in C++
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Files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
🧠 Learnings (8)
📚 Learning: 2025-09-23T15:12:38.312Z
Learnt from: nv-lschneider
Repo: NVIDIA/TensorRT-LLM PR: 7910
File: cpp/tensorrt_llm/thop/allreduceOp.cpp:352-446
Timestamp: 2025-09-23T15:12:38.312Z
Learning: In TensorRT-LLM NCCL device allreduce implementation (cpp/tensorrt_llm/thop/allreduceOp.cpp), the goto pattern in runNCCLAllReduceDeviceFusion is intentionally used for future extensibility, allowing multiple switch cases to fallback to the default handler. While not aesthetically ideal, this pattern supports adding more fusion cases later that can reuse the same fallback logic.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-08-19T03:35:20.866Z
Learnt from: djns99
Repo: NVIDIA/TensorRT-LLM PR: 6915
File: cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu:4616-4626
Timestamp: 2025-08-19T03:35:20.866Z
Learning: In the MOE profiler TMA workspace preparation (cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu), the overlapping of TMA WS regions for NONE and FINALIZE variants is deliberate design to save memory space, as confirmed by djns99. The comment "reuse the same pointers to save space" reflects this intentional behavior.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-08-09T20:57:04.084Z
Learnt from: sklevtsov-nvidia
Repo: NVIDIA/TensorRT-LLM PR: 3294
File: cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_gemm_tma_warp_specialized_input.cu:118-127
Timestamp: 2025-08-09T20:57:04.084Z
Learning: In the CUTLASS MoE finalize fusion implementation (cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_gemm_tma_warp_specialized_input.cu), when setting `fused_finalize_epilogue.stride_final_output` with shape `(hidden_size, num_output_tokens, 1)`, the `num_rows_in_final_output` should be set to `num_output_tokens` (not `hidden_size`) because of a swap+transpose operation that maps rows of the output tensor to `hidden_size` and columns to `num_output_tokens`.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-08-08T22:03:40.707Z
Learnt from: sklevtsov-nvidia
Repo: NVIDIA/TensorRT-LLM PR: 3294
File: cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu:1198-1209
Timestamp: 2025-08-08T22:03:40.707Z
Learning: In the CUTLASS MoE kernels (cpp/tensorrt_llm/cutlass_extensions), when `layout_info.fusion` is set to `TmaWarpSpecializedGroupedGemmInput::EpilogueFusion::FINALIZE`, the `router_scales` parameter must be non-null by design. The fused finalize kernel epilogue does not perform nullptr checks and requires valid router scales to function correctly. This is an implicit contract that callers must satisfy when enabling the FINALIZE fusion mode.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-09-23T14:58:05.372Z
Learnt from: nv-lschneider
Repo: NVIDIA/TensorRT-LLM PR: 7910
File: cpp/tensorrt_llm/kernels/nccl_device/config.cu:42-49
Timestamp: 2025-09-23T14:58:05.372Z
Learning: In TensorRT-LLM NCCL device kernels (cpp/tensorrt_llm/kernels/nccl_device/), the token partitioning intentionally uses ceil-like distribution (same token_per_rank for all ranks) to ensure all ranks launch the same number of blocks. This is required for optimal NCCL device API barrier performance, even though it may launch extra blocks for non-existent tokens on later ranks. Runtime bounds checking in the kernel (blockID validation) handles the overshoot cases.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-08-14T23:23:27.449Z
Learnt from: djns99
Repo: NVIDIA/TensorRT-LLM PR: 6915
File: cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu:4010-4012
Timestamp: 2025-08-14T23:23:27.449Z
Learning: For MOE (Mixture of Experts) code reviews in TensorRT-LLM, avoid repeatedly suggesting finalize fusion validation checks and safety assertions. The user djns99 has indicated these suggestions are repetitive and unwanted across multiple MOE-related changes.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-09-23T15:01:00.070Z
Learnt from: nv-lschneider
Repo: NVIDIA/TensorRT-LLM PR: 7910
File: cpp/tensorrt_llm/kernels/nccl_device/config.cu:15-17
Timestamp: 2025-09-23T15:01:00.070Z
Learning: In TensorRT-LLM NCCL device kernels, the <sstream> header is not needed as an explicit include in config.cu because it's provided transitively through other headers. Local compilation testing confirms this works without the explicit include.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
📚 Learning: 2025-09-19T21:28:13.751Z
Learnt from: jhaotingc
Repo: NVIDIA/TensorRT-LLM PR: 7856
File: cpp/tensorrt_llm/thop/fp8BlockScaleMoe.cpp:159-166
Timestamp: 2025-09-19T21:28:13.751Z
Learning: In TensorRT-LLM blockScaleMoe routing (cpp/tensorrt_llm/kernels/trtllmGenKernels/blockScaleMoe/runner.cu), the DeepSeek routing method performs reinterpret_cast<float*>(routingLogits) at line 89, which could cause issues if routing_logits are BF16. However, Qwen3-FP8 models use RenormalizeNaive routing method and are not affected by this dtype casting issue.
Applied to files:
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu
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🔇 Additional comments (3)
cpp/tensorrt_llm/kernels/communicationKernels/moeAlltoAllKernels.cu (3)
629-629: LGTM!The comment clearly documents the intent of the reduction logic across all TOP_K-specific code paths below.
680-713: LGTM!The TOP_K=10 reduction logic is correctly implemented using a three-stage tree reduction:
- Pair-wise: reduces 10 accumulators to 5 intermediate sums
- Partial merge: reduces to 3 intermediate sums
- Final merge: accumulates all into acc[0]
The pattern is consistent with other TOP_K cases and efficiently reduces the 10-way accumulation.
714-743: Critical control flow improvement: explicit mutual exclusivity.Changing from
if constexprtoelse if constexprmakes the mutually exclusive nature of these TOP_K branches explicit. Combined with the new TOP_K==10 case above, this ensures that:
- TOP_K=10 now has an optimized path instead of falling through to the generic fallback
- The control flow clearly signals one-and-only-one branch execution
- Future maintenance is less error-prone
This restructuring, along with the new TOP_K==10 case, resolves the bug mentioned in the PR title.
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…DIA#10197) Signed-off-by: Bo Li <22713281+bobboli@users.noreply.github.com>
…DIA#10197) Signed-off-by: Bo Li <22713281+bobboli@users.noreply.github.com> Signed-off-by: Daniil Kulko <kulkodaniil@gmail.com>
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