89 lines
3.2 KiB
Python
89 lines
3.2 KiB
Python
# SPDX-License-Identifier: Apache-2.0
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# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
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"""Fuser detection for the Transformers modeling backend.
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`get_fuser` traces a module class once (see `fx_utils`) and matches it against
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each concrete fuser in `fusers`; `Fusers` caches the result per class for a
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whole model. `base.recursive_replace` then applies the matched fuser per
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instance. RMSNorm-shaped modules the tracer cannot match are warned about.
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"""
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from collections import UserDict
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from typing import TYPE_CHECKING
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from cachetools import cached
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from torch import nn
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from vllm.logger import init_logger
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from vllm.model_executor.models.transformers.fusers import (
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BaseFuser,
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GLUFuser,
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MLAFuser,
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PackedQKVFuser,
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QKVFuser,
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RewriteFuser,
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RMSNormFuser,
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)
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from vllm.model_executor.models.transformers.fx_utils import trace
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if TYPE_CHECKING:
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from vllm.config import VllmConfig
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logger = init_logger(__name__)
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def key(module: nn.Module) -> tuple:
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"""Cache key for `get_fuser`. Considers module type and its immediate children."""
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return (type(module), tuple(name for name, _ in module.named_children()))
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@cached(cache={}, key=key)
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def get_fuser(module: nn.Module) -> BaseFuser | None:
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"""The fuser for `module`'s class and shape (cached), or `None` if no match."""
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# Projection fusions need >=2 sibling linears; the RMSNorm fusion needs a
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# leaf module (raw tensor math, no submodules). Nothing else can match, and
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# tracing is skipped for it.
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n_linear = sum(isinstance(c, nn.Linear) for c in module.children())
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is_leaf = next(module.children(), None) is None
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if n_linear < 2 and not is_leaf:
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return None
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if (graph := trace(module)) is None:
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return None
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for fuser_cls in (MLAFuser, GLUFuser, QKVFuser, PackedQKVFuser, RMSNormFuser):
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if (fuser := fuser_cls.match(graph, module)) is not None:
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if isinstance(fuser, RewriteFuser):
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try:
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fuser.update_forward(module)
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except Exception as exc:
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logger.debug(
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"Attempted to fuse %s using %s but failed "
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"to update its forward method: %s",
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type(module),
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fuser_cls.__name__,
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exc,
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)
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continue
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return fuser
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# A norm we could not match structurally is left unfused; flag likely misses.
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if module.__class__.__name__.endswith("RMSNorm"):
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logger.warning_once(
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"%s looks like an RMSNorm but its computation did not match the "
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"expected pattern, so it was left unfused.",
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module.__class__.__name__,
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)
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return None
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class Fusers(UserDict):
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"""Mapping from module class and shape to fuser, for all fusable modules."""
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def __init__(self, model: nn.Module, vllm_config: "VllmConfig"):
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self.vllm_config = vllm_config
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super().__init__({key(m): get_fuser(m) for m in model.modules()})
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def __getitem__(self, m: nn.Module) -> BaseFuser | None:
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fuser = self.data.get(key(m))
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if fuser is not None and fuser.validate(m, self.vllm_config):
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return fuser
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return None
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