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fix(vllm): default attention backend to TRITON_ATTN on ROCm #507

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Merged
HuangJoJo merged 1 commit into from
Oct 19, 2026
Merged

fix(vllm): default attention backend to TRITON_ATTN on ROCm #507

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7 changes: 6 additions & 1 deletion roll/third_party/vllm/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,12 @@ async def create_async_llm(resource_placement_groups: List[Dict], headless: bool
kwargs["enable_sleep_mode"] = True
if "attention_config" not in kwargs and "attention_config" in engine_arg_names:
# vllm<=0.12.0 does not have attention_config in AsyncEngineArgs.
kwargs["attention_config"] = {"backend": "FLASH_ATTN"}
# FLASH_ATTN needs the CUDA-only vllm_flash_attn package, so on ROCm it fails every engine
# at init with "AssertionError: FlashAttention version not detected." vLLM's own gfx942
# priority list does not contain FLASH_ATTN at all; TRITON_ATTN is the Triton
# FlashAttention implementation it ships for ROCm.
default_backend = "TRITON_ATTN" if current_platform.is_rocm() else "FLASH_ATTN"
kwargs["attention_config"] = {"backend": default_backend}

if "moe_backend" not in kwargs and "moe_backend" in engine_arg_names:
# vLLM0.20.0, remove this while >= 0.29: https://github.com/vllm-project/vllm/issues/45447
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