vllm.compilation.passes.fusion.attn_quant_fusion ¶

class AttnFp8StaticQuantPattern(VllmPatternReplacement[..., torch.Tensor]):
    """
    Fusion for Attention+Fp8StaticQuant.

    Only triggers when the attention implementation returns True in
    `fused_output_quant_supported()`. If the pattern is found, the
    Fp8StaticQuant op will be removed from the graph, and its scale
    will be passed into Attention op as the `output_scale` argument.
    """

    def __init__(self, layer: Attention, dtype: torch.dtype):
        self._layer_name = layer.layer_name
        self._num_heads = layer.num_heads
        self._head_size = layer.head_size
        self._dtype = dtype
        self._quant_matcher = MatcherQuantFP8(_FP8_QUANT_KEY)

    @property
    def pattern(self) -> Callable[..., torch.Tensor]:
        # When _USE_LAYERNAME is enabled (torch >= 2.11), layer_name is
        # passed as an explicit pattern input so the pattern matcher
        # treats it as a wildcard matching hoisted LayerName placeholders.
        # Otherwise it stays as a closure constant (original behavior).
        _ln = _encode_layer_name(self._layer_name)

        if _USE_LAYERNAME:

            def _pattern_with_ln(  # type: ignore[misc]
                q, k, v, output_attn, scale, kv_cache_dummy_dep, layer_name
            ):
                at1 = auto_functionalized(
                    ATTN_OP,
                    query=q,
                    key=k,
                    value=v,
                    output=output_attn,
                    layer_name=layer_name,
                    output_scale=None,
                    output_block_scale=None,
                    kv_cache_dummy_dep=kv_cache_dummy_dep,
                )
                attn_out_view = RESHAPE_OP(
                    at1[1], [q.shape[0], self._num_heads * self._head_size]
                )
                return self._quant_matcher(attn_out_view, scale)[0]

            return _pattern_with_ln

        def _pattern(q, k, v, output_attn, scale, kv_cache_dummy_dep):
            at1 = auto_functionalized(
                ATTN_OP,
                query=q,
                key=k,
                value=v,
                output=output_attn,
                layer_name=_ln,
                output_scale=None,
                output_block_scale=None,
                kv_cache_dummy_dep=kv_cache_dummy_dep,
            )
            attn_out_view = RESHAPE_OP(
                at1[1], [q.shape[0], self._num_heads * self._head_size]
            )
            return self._quant_matcher(attn_out_view, scale)[0]

        return _pattern

    @property
    def replacement(self) -> Callable[..., torch.Tensor]:
        _ln = _encode_layer_name(self._layer_name)

        if _USE_LAYERNAME:

            def _replacement_with_ln(  # type: ignore[misc]
                q, k, v, output_attn, scale, kv_cache_dummy_dep, layer_name
            ):
                output_attn = torch.empty(
                    [q.shape[0], self._num_heads, self._head_size],
                    dtype=FP8_DTYPE,
                    device=q.device,
                )
                at1 = auto_functionalized(
                    ATTN_OP,
                    query=q,
                    key=k,
                    value=v,
                    output=output_attn,
                    layer_name=layer_name,
                    output_scale=scale,
                    output_block_scale=None,
                    kv_cache_dummy_dep=kv_cache_dummy_dep,
                )
                return RESHAPE_OP(at1[1], [-1, self._num_heads * self._head_size])

            return _replacement_with_ln

        def _replacement(q, k, v, output_attn, scale, kv_cache_dummy_dep):
            output_attn = torch.empty(
                [q.shape[0], self._num_heads, self._head_size],
                dtype=FP8_DTYPE,
                device=q.device,
            )
            at1 = auto_functionalized(
                ATTN_OP,
                query=q,
                key=k,
                value=v,
                output=output_attn,
                layer_name=_ln,
                output_scale=scale,
                output_block_scale=None,
                kv_cache_dummy_dep=kv_cache_dummy_dep,
            )
            return RESHAPE_OP(at1[1], [-1, self._num_heads * self._head_size])

        return _replacement

    def get_inputs(self):
        dtype = self._dtype
        num_heads = self._num_heads
        head_size = self._head_size
        inputs: list = [
            self.empty(5, num_heads, head_size, dtype=dtype),  # q
            self.empty(5, num_heads, head_size, dtype=dtype),  # k
            self.empty(5, num_heads, head_size, dtype=dtype),  # v
            self.empty(5, num_heads, head_size, dtype=dtype),  # attn_output
            self.empty_fp32(1, 1),  # scale
            self.empty(0, dtype=dtype),  # kv_cache_dummy_dep
        ]
        if _USE_LAYERNAME:
            inputs.append(_encode_layer_name(self._layer_name))
        return inputs

class AttnNvfp4QuantPattern(
    VllmPatternReplacement[..., tuple[torch.Tensor, torch.Tensor]]
):
    """
    Fusion for Attention+Nvfp4Quant.

    Only triggers when the attention implementation returns True in
    `fused_output_quant_supported()`. If the pattern is found, the
    Nvfp4Quant op will be removed from the graph, and its scale
    will be passed into Attention op as the `output_scale` argument.
    """

    def __init__(self, layer: Attention, dtype: torch.dtype):
        self._layer_name = layer.layer_name
        self._num_heads = layer.num_heads
        self._head_size = layer.head_size
        self._dtype = dtype
        self._QUANT_OP = QUANT_OPS[kNvfp4Dynamic]

    @property
    def pattern(self) -> Callable[..., tuple[torch.Tensor, torch.Tensor]]:
        _ln = _encode_layer_name(self._layer_name)

        if _USE_LAYERNAME:

            def _pattern_with_ln(  # type: ignore[misc]
                q,
                k,
                v,
                output_attn,
                output_quant,
                output_scale,
                input_scale,
                kv_cache_dummy_dep,
                layer_name,
            ):
                at1 = auto_functionalized(
                    ATTN_OP,
                    query=q,
                    key=k,
                    value=v,
                    output=output_attn,
                    layer_name=layer_name,
                    output_scale=None,
                    output_block_scale=None,
                    kv_cache_dummy_dep=kv_cache_dummy_dep,
                )
                attn_out_view = RESHAPE_OP(
                    at1[1], [q.shape[0], self._num_heads * self._head_size]
                )
                at2 = auto_functionalized(
                    self._QUANT_OP,
                    input=attn_out_view,
                    input_scale=input_scale,
                    is_sf_swizzled_layout=True,
                    output=output_quant,
                    output_scale=output_scale,
                )
                return at2[1], torch.ops.aten.view.dtype(at2[2], FP8_DTYPE)

            return _pattern_with_ln

        def _pattern(
            q,
            k,
            v,
            output_attn,
            output_quant,
            output_scale,
            input_scale,
            kv_cache_dummy_dep,
        ):
            at1 = auto_functionalized(
                ATTN_OP,
                query=q,
                key=k,
                value=v,
                output=output_attn,
                layer_name=_ln,
                output_scale=None,
                output_block_scale=None,
                kv_cache_dummy_dep=kv_cache_dummy_dep,
            )
            attn_out_view = RESHAPE_OP(
                at1[1], [q.shape[0], self._num_heads * self._head_size]
            )
            at2 = auto_functionalized(
                self._QUANT_OP,
                input=attn_out_view,
                input_scale=input_scale,
                is_sf_swizzled_layout=True,
                output=output_quant,
                output_scale=output_scale,
            )
            return at2[1], torch.ops.aten.view.dtype(at2[2], FP8_DTYPE)

        return _pattern

    @property
    def replacement(self) -> Callable[..., tuple[torch.Tensor, torch.Tensor]]:
        _ln = _encode_layer_name(self._layer_name)

        if _USE_LAYERNAME:

            def _replacement_with_ln(  # type: ignore[misc]
                q,
                k,
                v,
                output_attn,
                _output_quant,
                output_scale,
                input_scale,
                kv_cache_dummy_dep,
                layer_name,
            ):
                output_attn = torch.empty(
                    [q.shape[0], self._num_heads, self._head_size // 2],
                    dtype=FP4_DTYPE,
                    device=q.device,
                )
                osv = torch.ops.aten.view.dtype(output_scale, FP8_DTYPE)
                at2 = auto_functionalized(
                    ATTN_OP,
                    query=q,
                    key=k,
                    value=v,
                    output=output_attn,
                    layer_name=layer_name,
                    output_scale=input_scale,
                    output_block_scale=osv,
                    kv_cache_dummy_dep=kv_cache_dummy_dep,
                )
                return RESHAPE_OP(
                    at2[1], [-1, self._num_heads * self._head_size // 2]
                ), at2[2]

            return _replacement_with_ln

        def _replacement(
            q,
            k,
            v,
            output_attn,
            _output_quant,
            output_scale,
            input_scale,
            kv_cache_dummy_dep,
        ):
            output_attn = torch.empty(
                [q.shape[0], self._num_heads, self._head_size // 2],
                dtype=FP4_DTYPE,
                device=q.device,
            )
            osv = torch.ops.aten.view.dtype(output_scale, FP8_DTYPE)
            at2 = auto_functionalized(
                ATTN_OP,
                query=q,
                key=k,
                value=v,
                output=output_attn,
                layer_name=_ln,
                output_scale=input_scale,
                output_block_scale=osv,
                kv_cache_dummy_dep=kv_cache_dummy_dep,
            )
            return RESHAPE_OP(
                at2[1], [-1, self._num_heads * self._head_size // 2]
            ), at2[2]

        return _replacement

    def get_inputs(self):
        dtype = self._dtype
        num_heads = self._num_heads
        head_size = self._head_size
        inputs: list = [
            self.empty_bf16(5, num_heads, head_size),  # q
            self.empty_bf16(5, num_heads, head_size),  # k
            self.empty_bf16(5, num_heads, head_size),  # v
            self.empty_bf16(5, num_heads, head_size),  # output_attn
            self.empty(5, num_heads * head_size // 2, dtype=FP4_DTYPE),
            self.empty_i32(128, round_up(num_heads * head_size // 16, 4)),
            self.empty_fp32(1, 1),  # input_scale
            self.empty(0, dtype=dtype),  # kv_cache_dummy_dep
        ]
        if _USE_LAYERNAME:
            inputs.append(_encode_layer_name(self._layer_name))
        return inputs

class AttnQuantFusionPass(VllmFusionPatternMatcherPass):
    """
    This pass fuses post-attention quantization onto attention if supported.

    It uses the pattern matcher and matches each layer manually, as strings
    cannot be wildcarded. This also lets us check support on attention layers
    upon registration instead of during pattern matching.

    Currently, only static fp8 quant is supported, but patterns could easily be
    added for other quant schemes and dtypes. The bigger hurdle for wider
    support are attention kernels, which need to support fusing output quant.
    """

    def __init__(self, config: VllmConfig) -> None:
        super().__init__(config, "attn_quant_fusion")

        dtype = config.model_config.dtype
        layers = list(get_layers_from_vllm_config(config, Attention).values())

        if len(layers) == 0:
            logger.warning(
                "Attention + quant fusion is enabled, but no attention layers "
                "were found in CompilationConfig.static_forward_context "
                "so no fusion patterns were registered."
            )

        # When _USE_LAYERNAME is enabled, layer_name is a wildcard so all
        # layers produce the same pattern — register once then break.
        for layer in layers:
            if layer.impl.fused_output_quant_supported(_FP8_QUANT_KEY):
                self.register(AttnFp8StaticQuantPattern(layer, dtype))
                if _USE_LAYERNAME:
                    break

        if current_platform.is_cuda() and hasattr(torch.ops._C, "scaled_fp4_quant"):
            for layer in layers:
                if layer.impl.fused_output_quant_supported(kNvfp4Dynamic):
                    self.register(AttnNvfp4QuantPattern(layer, dtype))
                    if _USE_LAYERNAME:
                        break

        self.dump_patterns(config, self.pm_pass)