New allgathervdispatcher for inference and simplify old dispatcher. #4258
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sidsingh-nvidia merged 69 commits intoApr 30, 2026
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5 tasks
- Fix NCCLAllGatherDispatcher.set_step_metadata writing _valid_tokens_tensor to the subclass instead of InferenceAllGatherDispatcherBase, causing the Triton kernel to receive None and crash with 'constexpr has no attr is_ptr' - Add use_allgather_v support to NCCLAllGatherDispatcher: non-CG steps (prefill) all-gather actual per-rank token counts, pad to max, AllGather, compact on dispatch; expand, ReduceScatter, truncate on combine - Context passes use_allgather_v=not using_cuda_graph_this_step() for NCCL; both context and wrapper now all-gather actual per-rank counts rather than trivially filling (dummy forward always eager → use_allgather_v=True) - Fix using_cuda_graph_this_step missing parentheses (property → method call)
ko3n1g
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Apr 30, 2026
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/claude review |
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🔄 Merge queue validation started! You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25182866696 |
…ers the case where one rank is running eager prefill with max_tokens, and other ranks are running a decode cuda graph with 1 token
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🔄 Merge queue validation started! You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25188712125 |
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What does this PR do ?
Introduces a new dispatcher for moe inference based on allgatherv's. This helps us run MoEs without any complicated "ep syncs" to figure out compatible cuda-graphs.
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