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[Bugfix] Gracefully disable AllReduceFusionPass on GPUs without multicast support #35085

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Merged
vllm-bot merged 2 commits into from
Feb 25, 2026
Merged

[Bugfix] Gracefully disable AllReduceFusionPass on GPUs without multicast support #35085

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ad3c3ab
[Bugfix] Gracefully disable AllReduceFusionPass on GPUs without multi…
haosdent Feb 23, 2026
74d8949
[Bugfix] Gracefully disable AllReduceFusionPass on GPUs without multi…
haosdent Feb 24, 2026
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28 changes: 20 additions & 8 deletions vllm/compilation/passes/fusion/allreduce_rms_fusion.py
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Original file line number Diff line number Diff line change
Expand Up @@ -729,14 +729,26 @@ def __init__(self, config: VllmConfig) -> None:
scope="global",
)

self.workspace = flashinfer_comm.create_allreduce_fusion_workspace(
backend="trtllm",
world_size=self.tp_size,
rank=rank,
max_token_num=self.max_token_num,
hidden_dim=self.hidden_dim,
dtype=self.model_dtype,
)
try:
self.workspace = flashinfer_comm.create_allreduce_fusion_workspace(
backend="trtllm",
world_size=self.tp_size,
rank=rank,
max_token_num=self.max_token_num,
hidden_dim=self.hidden_dim,
dtype=self.model_dtype,
)
except RuntimeError as e:
if "multicast" not in str(e).lower():
raise
logger.warning_once(
"AllReduce fusion pass is disabled: flashinfer workspace "
"creation failed: %s. This is expected on GPUs without "
"NVSwitch (e.g., NVLink bridge-only or PCIe topologies). "
"Falling back to non-fused allreduce.",
str(e),
)
return

global _FI_WORKSPACE
_FI_WORKSPACE = self.workspace
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