vllm-omni/vllm_omni/diffusion/layers/norm.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project

from importlib.util import find_spec

import torch
import torch.nn as nn
import torch.nn.functional as F
from vllm.logger import init_logger

from vllm_omni.diffusion.layers.custom_op import CustomOp

logger = init_logger(__name__)

_HAS_MINDIESD = find_spec("mindiesd") is not None


class LayerNorm(nn.LayerNorm, CustomOp):
    """
    LayerNorm implementation that inherits from both ``nn.LayerNorm`` and ``CustomOp``.
    NPU:
        Uses ``mindiesd.fast_layernorm(self, x)`` when MindIE-SD is installed.
    CUDA / HIP / XPU / native:
        Falls back to FP32 nn.LayerNorm implementation.
    """

    def __init__(self, dim: int, eps: float = 1e-6, elementwise_affine: bool = True):
        super().__init__(normalized_shape=dim, eps=eps, elementwise_affine=elementwise_affine)
        # CustomOp.__init__ cannot be called here because it would re-run
        # nn.Module initialization and clear LayerNorm parameters.
        self._forward_method = CustomOp.dispatch_forward(self)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        return self._forward_method(x)

    def forward_cuda(self, x: torch.Tensor) -> torch.Tensor:
        return self.forward_native(x)

    def forward_hip(self, x: torch.Tensor) -> torch.Tensor:
        return self.forward_native(x)

    def forward_npu(self, x: torch.Tensor) -> torch.Tensor:
        if _HAS_MINDIESD:
            try:
                from mindiesd import fast_layernorm

                return fast_layernorm(self, x)
            except ImportError as e:
                logger.warning_once(
                    "mindiesd.fast_layernorm import failed, falling back to FP32 layer_norm: %s",
                    e,
                )

        return self.forward_native(x)

    def forward_native(self, x: torch.Tensor) -> torch.Tensor:
        origin_dtype = x.dtype
        return F.layer_norm(
            x.float(),
            self.normalized_shape,
            self.weight.float() if self.weight is not None else None,
            self.bias.float() if self.bias is not None else None,
            self.eps,
        ).to(origin_dtype)


class RMSNorm(CustomOp):
    def __init__(self, hidden_size: int, eps: float = 1e-6, dtype: torch.dtype | None = None) -> None:
        super().__init__()
        weight_dtype = dtype or torch.get_default_dtype()
        self.weight = nn.Parameter(torch.ones(hidden_size, dtype=weight_dtype))
        self.hidden_size = hidden_size
        self.variance_epsilon = eps

    def _forward_fused(self, x: torch.Tensor) -> torch.Tensor:
        from vllm._custom_ops import rms_norm as fused_rms_norm

        orig_shape = x.shape
        hidden_size = orig_shape[-1]
        x_2d = x.reshape(-1, hidden_size)
        out = torch.empty_like(x_2d)
        fused_rms_norm(out, x_2d, self.weight.data, self.variance_epsilon)
        return out.reshape(orig_shape)

    def forward_cuda(
        self,
        x: torch.Tensor,
        residual: torch.Tensor | None = None,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        if residual is not None:
            return self.forward_native(x, residual)
        # During torch.compile tracing, fused_rms_norm writes to `out` in-place
        # (returns None) and accesses self.weight.data, which is a DTensor under
        # HSDP. Both patterns confuse inductor's compute_ancestors scheduler.
        # Fall back to forward_native so inductor can fuse the pure-PyTorch ops
        # itself.
        if torch.compiler.is_compiling():
            return self.forward_native(x)
        try:
            return self._forward_fused(x)
        except Exception:
            return self.forward_native(x)

    def forward_hip(
        self,
        x: torch.Tensor,
        residual: torch.Tensor | None = None,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        if residual is not None:
            return self.forward_native(x, residual)
        if torch.compiler.is_compiling():
            return self.forward_native(x)
        try:
            return self._forward_fused(x)
        except Exception:
            return self.forward_native(x)

    def forward_musa(
        self,
        x: torch.Tensor,
        residual: torch.Tensor | None = None,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        if residual is not None:
            return self.forward_native(x, residual)
        # Preserve the aten::rms_norm graph so dynamic Inductor can fuse the
        # H3 Q/K norm with its inline RoPE path on MUSA.
        return F.rms_norm(
            x,
            (self.hidden_size,),
            self.weight,
            self.variance_epsilon,
        )

    def forward_npu(
        self,
        x: torch.Tensor,
        residual: torch.Tensor | None = None,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        import torch_npu

        if residual is not None:
            output, _, updated_residual = torch_npu.npu_add_rms_norm(
                x,
                residual,
                self.weight,
                self.variance_epsilon,
            )
            return output, updated_residual

        output = torch_npu.npu_rms_norm(x, gamma=self.weight, epsilon=self.variance_epsilon)[0]

        return output

    def forward_native(
        self,
        x: torch.Tensor,
        residual: torch.Tensor | None = None,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        if residual is not None:
            residual = residual + x
            x = residual
        input_dtype = x.dtype
        x = x.to(torch.float32)
        variance = x.pow(2).mean(-1, keepdim=True)
        out = x * torch.rsqrt(variance + self.variance_epsilon)
        out = self.weight.to(torch.float32) * out
        out = out.to(input_dtype)
        return (out, residual) if residual is not None else out