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use combo kernel to fuse qk-norm and qk-rope #26682

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Merged
merged 2 commits into from
Oct 14, 2025
Merged

use combo kernel to fuse qk-norm and qk-rope #26682

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506a52f
use combo kernel
BoyuanFeng Oct 13, 2025
00f4fca
respect user inductor config
BoyuanFeng Oct 13, 2025
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9 changes: 9 additions & 0 deletions vllm/config/compilation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -367,6 +367,11 @@ class CompilationConfig:
since we know all keys are in a range [0, max_capture_size],
we can optimize it to list[int] for better lookup performance."""

use_horizontal_fusion = True
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@gemini-code-assist gemini-code-assist bot Oct 13, 2025

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high

The use_horizontal_fusion flag is enabled by default. This will automatically enable the combo_kernels feature in PyTorch Inductor for users on versions 2.9.0.dev or newer. Since this relies on a feature in a development version of PyTorch, it may be unstable. It would be safer to set this to False by default to prevent potential issues for users on bleeding-edge PyTorch versions. Users can then explicitly opt-in to enable this experimental feature.

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use_horizontal_fusion = True
use_horizontal_fusion = False

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@BoyuanFeng BoyuanFeng Oct 13, 2025

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We want to enable by default since it benefits models in general.

"""Whether use horizontal fusion. This is
useful for fusing qk-norm and qk-rope when query and key have
different shapes."""

# keep track of enabled and disabled custom ops
enabled_custom_ops: Counter[str] = field(default_factory=Counter, init=False)
"""custom ops that are enabled"""
Expand Down Expand Up @@ -498,6 +503,10 @@ def __post_init__(self) -> None:
if isinstance(self.pass_config, dict):
self.pass_config = PassConfig(**self.pass_config)

if self.use_horizontal_fusion and is_torch_equal_or_newer("2.9.0.dev"):
self.inductor_compile_config["combo_kernels"] = True
self.inductor_compile_config["benchmark_combo_kernel"] = True

# migrate the deprecated flags
if not self.use_cudagraph:
logger.warning(
Expand Down