[Feature]: support for pipeline parallelism under speculative decoding in PyTorch workflow
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@laikhtewari is already working on this.
Since Nov 7, 2025.
feature request
Pytorch
Scale-out
Speculative Decoding
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Description
🚀 The feature, motivation and pitch
As of TRT-LLM 1.2.0rc2, attempting to use speculative decoding in the PyTorch workflow (in this case, N-gram speculative decoding) with a pipeline parallel size > 1 results in the following error at initialization time:
File "/virtualenv/lib/python3.12/site-packages/tensorrt_llm/_torch/pyexecutor/py_executor.py", line 293, in __init__
raise NotImplementedError(
^^^^^^^^^^^^^^^^^
NotImplementedError: Drafting is not supported for selected executor loop. Please disable disagg/pipeline parallelism scheduler.
Which implies that support for this configuration is simply not present. It would be great if this could be fixed, so as to enable use of speculative decoding with pipeline parallelism.
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