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sglang/python/sglang/multimodal_gen/runtime/layers/layernorm.py
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Python

# Copied and adapted from: https://github.com/hao-ai-lab/FastVideo
# SPDX-License-Identifier: Apache-2.0
# Adapted from vllm: https://github.com/vllm-project/vllm/blob/v0.7.3/vllm/model_executor/layers/layernorm.py
"""Custom normalization layers."""
from typing import Optional, Tuple, Union
import torch
import torch.nn as nn
import torch.nn.functional as F
from sglang.multimodal_gen.runtime.platforms import current_platform
_is_cuda = current_platform.is_cuda()
_is_npu = current_platform.is_npu()
if _is_cuda:
from sgl_kernel import fused_add_rmsnorm, rmsnorm
if _is_npu:
import torch_npu
from sglang.jit_kernel.diffusion.triton.norm import norm_infer, rms_norm_fn
from sglang.jit_kernel.diffusion.triton.rmsnorm_onepass import triton_one_pass_rms_norm
from sglang.jit_kernel.diffusion.triton.scale_shift import fuse_scale_shift_kernel
from sglang.jit_kernel.norm import can_use_fused_inplace_qknorm, fused_inplace_qknorm
from sglang.multimodal_gen.runtime.distributed.parallel_state import (
get_tensor_model_parallel_rank,
get_tensor_model_parallel_world_size,
get_tp_group,
)
from sglang.multimodal_gen.runtime.layers.custom_op import CustomOp
from sglang.multimodal_gen.runtime.utils.common import get_bool_env_var
# Copied and adapted from sglang
@CustomOp.register("rms_norm")
class RMSNorm(CustomOp):
"""Root mean square normalization.
Computes x -> w * x / sqrt(E[x^2] + eps) where w is the learned weight.
Refer to https://arxiv.org/abs/1910.07467
"""
def __init__(
self,
hidden_size: int,
eps: float = 1e-6,
dtype: torch.dtype = torch.float32,
var_hidden_size: Optional[int] = None,
) -> None:
super().__init__()
self.weight = nn.Parameter(torch.ones(hidden_size))
self.variance_epsilon = eps
self.hidden_size = hidden_size
self.variance_size_override = (
None if var_hidden_size == hidden_size else var_hidden_size
)
if get_bool_env_var("SGLANG_ENABLE_DETERMINISTIC_INFERENCE"):
self._forward_method = self.forward_native
def forward_triton(self, x: torch.Tensor, residual: Optional[torch.Tensor] = None):
return rms_norm_fn(
x, self.weight, bias=None, residual=residual, eps=self.variance_epsilon
)
def forward_cuda(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
shape = x.shape
device = x.device
x = x.reshape(-1, shape[-1])
if residual is not None:
residual_shape = residual.shape
residual = residual.view(-1, shape[-1])
if x.dtype == torch.float:
# fp32
out = self.forward_triton(x, residual)
if residual is not None:
return out[0].view(shape), out[1].view(residual_shape)
out = out.view(shape)
return out
elif self.variance_size_override is not None:
return self.forward_native(x, residual)
elif residual is not None:
fused_add_rmsnorm(x, residual, self.weight.data, self.variance_epsilon)
return x.view(shape), residual.view(residual_shape)
else:
if x.shape[-1] <= 128:
out = triton_one_pass_rms_norm(
x, self.weight.data, self.variance_epsilon
)
else:
out = rmsnorm(x, self.weight.data, self.variance_epsilon)
out = out.view(shape)
return out
def forward_native(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if not x.is_contiguous():
x = x.contiguous()
orig_dtype = x.dtype
x = x.to(torch.float32)
if residual is not None:
x = x + residual.to(torch.float32)
residual = x.to(orig_dtype)
hidden_size = x.shape[-1]
if hidden_size != self.hidden_size:
raise ValueError(
"Expected hidden_size to be "
f"{self.hidden_size}, but found: {hidden_size}"
)
if self.variance_size_override is None:
x_var = x
else:
if hidden_size < self.variance_size_override:
raise ValueError(
"Expected hidden_size to be at least "
f"{self.variance_size_override}, but found: {hidden_size}"
)
x_var = x[..., : self.variance_size_override]
variance = x_var.pow(2).mean(dim=-1, keepdim=True)
x = x * torch.rsqrt(variance + self.variance_epsilon)
x = (x * self.weight).to(orig_dtype)
if residual is None:
return x
else:
return x, residual
def forward_cpu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
return self.forward_native(x, residual)
def forward_npu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if residual is not None:
out, _, residual_out = torch_npu.npu_add_rms_norm(
residual, x, self.weight.data, self.variance_epsilon
)
return out, residual_out
return torch_npu.npu_rms_norm(x, self.weight.data, self.variance_epsilon)[0]
def forward_hip(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
# ROCm builds of sgl-kernel do not expose rmsnorm custom ops yet.
return self.forward_native(x, residual)
def extra_repr(self) -> str:
s = f"hidden_size={self.weight.data.size(0)}"
s += f", eps={self.variance_epsilon}"
return s
# Copied and adapted from sglang
@CustomOp.register("layer_norm")
class LayerNorm(CustomOp):
def __init__(
self,
hidden_size: int,
eps=1e-5,
bias: bool = True,
elementwise_affine=True,
device=None,
dtype=None,
) -> None:
super().__init__()
self.eps = eps
factory_kwargs = {"device": device, "dtype": dtype}
self.hidden_size = hidden_size
if elementwise_affine:
self.weight = torch.nn.Parameter(torch.empty(hidden_size, **factory_kwargs))
self.bias = (
torch.nn.Parameter(torch.empty(hidden_size, **factory_kwargs))
if bias
else None
)
else:
self.register_parameter("weight", None)
self.register_parameter("bias", None)
# Lazy cache for ones vector (not a registered buffer to avoid FSDP/meta issues)
self._weight_fallback_cache = None
def _get_weight_fallback(self, x: torch.Tensor) -> torch.Tensor:
wf = getattr(self, "_weight_fallback_cache", None)
if (
wf is None
or wf.device != x.device
or wf.dtype != x.dtype
or wf.numel() != self.hidden_size
):
wf = torch.ones(self.hidden_size, device=x.device, dtype=x.dtype)
self._weight_fallback_cache = wf
return wf
def forward_triton(self, x: torch.Tensor):
# Fast inference kernel without residual/dropout branches
return norm_infer(
x.view(-1, self.hidden_size),
self.weight,
self.bias,
eps=self.eps,
is_rms_norm=False,
).view(x.shape)
def forward_cuda(
self,
x: torch.Tensor,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
shape = x.shape
x = x.view(-1, self.hidden_size)
return self.forward_triton(x).view(shape)
@torch.compile(backend="inductor", disable=current_platform.is_npu())
def forward_native(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
input_dtype = x.dtype
mean = x.mean(-1, keepdim=True)
variance = (x - mean).pow(2).mean(-1, keepdim=True)
x = (x - mean) * torch.rsqrt(variance + self.eps)
if self.weight is not None:
x = self.weight * x
# if no affine, this is a no-op
if self.bias is not None:
x = x + self.bias
return x.to(input_dtype)
def forward_cpu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
return self.forward_native(x, residual)
def extra_repr(self) -> str:
s = f"hidden_size={self.weight.data.size(0)}"
s += f", eps={self.variance_epsilon}"
return s
# adapted from Diffusers: https://github.com/huggingface/diffusers/blob/main/src/diffusers/models/normalization.py
# NOTE(will): Needed to match behavior of diffusers and wan2.1 even while using
# FSDP's MixedPrecisionPolicy
class FP32LayerNorm(nn.LayerNorm):
def forward(self, inputs: torch.Tensor) -> torch.Tensor:
origin_dtype = inputs.dtype
device = inputs.device
return F.layer_norm(
inputs.float(),
self.normalized_shape,
self.weight.float().to(device=device) if self.weight is not None else None,
self.bias.float().to(device=device) if self.bias is not None else None,
self.eps,
).to(origin_dtype)
################################################################################
# Fused norm kernel
################################################################################
def _ensure_contiguous(tensor: Optional[torch.Tensor]) -> Optional[torch.Tensor]:
return tensor.contiguous() if tensor is not None else None
class _ScaleResidualNormScaleShift(CustomOp):
"""
Fused kernel that combines:
1. residual_out = residual + gate * x
2. normed = layernorm(residual_out) or rmsnorm(residual_out)
3. out = normed * (1 + scale) + shift
compute_dtype is always fp32 for higher precision.
"""
norm_type: str
def __init__(
self,
hidden_size: int,
eps: float = 1e-6,
elementwise_affine: bool = False,
dtype: torch.dtype = torch.float32,
prefix: str = "",
):
super().__init__()
self.eps = eps
self.dtype = dtype
if self.norm_type == "rms":
self.norm = RMSNorm(hidden_size, eps=eps, dtype=dtype)
elif self.norm_type == "layer":
self.norm = FP32LayerNorm(
hidden_size, elementwise_affine=elementwise_affine, eps=eps, dtype=dtype
)
else:
raise NotImplementedError(f"Norm type {self.norm_type} not implemented")
def forward_cuda(
self,
residual: torch.Tensor,
x: torch.Tensor,
gate: torch.Tensor | int,
shift: torch.Tensor,
scale: torch.Tensor,
) -> tuple[torch.Tensor, torch.Tensor]:
if x.shape[-1] % 256 != 0 and x.shape[-1] <= 8192:
import warnings
warnings.warn(
"FusedScaleResidualNormScaleShift cuda not available, using native fallback",
stacklevel=2,
)
return self.forward_native(residual, x, gate, shift, scale)
from sglang.jit_kernel.diffusion.cutedsl.scale_residual_norm_scale_shift import (
fused_scale_residual_norm_scale_shift,
)
if isinstance(gate, int) and gate != 1:
raise ValueError(
f"Only gate value of 1 is supported for int type, but got {gate}"
)
return fused_scale_residual_norm_scale_shift(
residual.contiguous(),
x.contiguous(),
gate.contiguous() if isinstance(gate, torch.Tensor) else None,
_ensure_contiguous(getattr(self.norm, "weight", None)),
_ensure_contiguous(getattr(self.norm, "bias", None)),
scale.contiguous(),
shift.contiguous(),
self.norm_type,
self.eps,
)
def forward_hip(self, *args, **kwargs):
# ROCm does not support CUDA/CUTLASS-based fused kernels yet,
# so we fall back to the native PyTorch implementation.
return self.forward_native(*args, **kwargs)
def forward_native(
self,
residual: torch.Tensor,
x: torch.Tensor,
gate: torch.Tensor | int,
shift: torch.Tensor,
scale: torch.Tensor,
) -> tuple[torch.Tensor, torch.Tensor]:
# x.shape: [batch_size, seq_len, inner_dim]
if isinstance(gate, int):
# used by cross-attention, should be 1
assert gate == 1
residual_output = residual + x
elif isinstance(gate, torch.Tensor):
if gate.dim() == 4:
# gate.shape: [batch_size, num_frames, 1, inner_dim]
num_frames = gate.shape[1]
frame_seqlen = x.shape[1] // num_frames
residual_output = residual + (
x.unflatten(dim=1, sizes=(num_frames, frame_seqlen)) * gate
).flatten(1, 2)
else:
# gate.shape: [batch_size, 1, inner_dim]
residual_output = residual + x * gate
else:
raise ValueError(f"Gate type {type(gate)} not supported")
normalized = self.norm(residual_output)
modulated = fuse_scale_shift_kernel(normalized, scale, shift)
return modulated, residual_output
class ScaleResidualLayerNormScaleShift(_ScaleResidualNormScaleShift):
norm_type = "layer"
class ScaleResidualRMSNormScaleShift(_ScaleResidualNormScaleShift):
norm_type = "rms"
class _NormScaleShift(CustomOp):
"""
Fused kernel that combines:
1. normed = layernorm(x) or rmsnorm(x)
2. out = normed * (1 + scale) + shift
compute_dtype is always fp32 for higher precision.
"""
norm_type: str
def __init__(
self,
hidden_size: int,
eps: float = 1e-6,
elementwise_affine: bool = False,
dtype: torch.dtype = torch.float32,
prefix: str = "",
):
super().__init__()
self.eps = eps
if self.norm_type == "rms":
self.norm = RMSNorm(hidden_size, eps=eps, dtype=dtype)
elif self.norm_type == "layer":
self.norm = FP32LayerNorm(
hidden_size, elementwise_affine=elementwise_affine, eps=eps, dtype=dtype
)
else:
raise NotImplementedError(f"Norm type {self.norm_type} not implemented")
def forward_cuda(
self, x: torch.Tensor, shift: torch.Tensor, scale: torch.Tensor
) -> torch.Tensor:
if x.shape[-1] % 256 != 0 and x.shape[-1] <= 8192:
import warnings
warnings.warn(
"FusedNormScaleShift cuda not available, using native fallback",
stacklevel=2,
)
return self.forward_native(x, shift, scale)
from sglang.jit_kernel.diffusion.cutedsl.scale_residual_norm_scale_shift import (
fused_norm_scale_shift,
)
return fused_norm_scale_shift(
x.contiguous(),
_ensure_contiguous(getattr(self.norm, "weight", None)),
_ensure_contiguous(getattr(self.norm, "bias", None)),
scale.contiguous(),
shift.contiguous(),
self.norm_type,
self.eps,
)
def forward_hip(self, *args, **kwargs):
# ROCm does not support CUDA/CUTLASS-based fused kernels yet,
# so we fall back to the native PyTorch implementation.
return self.forward_native(*args, **kwargs)
def forward_native(
self, x: torch.Tensor, shift: torch.Tensor, scale: torch.Tensor
) -> torch.Tensor:
normalized = self.norm(x)
modulated = fuse_scale_shift_kernel(normalized, scale, shift)
return modulated.to(x.dtype)
class LayerNormScaleShift(_NormScaleShift):
norm_type = "layer"
class RMSNormScaleShift(_NormScaleShift):
norm_type = "rms"
def apply_qk_norm(
q: torch.Tensor,
k: torch.Tensor,
q_norm: "RMSNorm",
k_norm: "RMSNorm",
head_dim: int,
allow_inplace: bool = True,
) -> Tuple[torch.Tensor, torch.Tensor]:
"""Apply QK normalization for query and key tensors.
Uses JIT fused inplace kernel when available, falls back to standard RMSNorm.
"""
batch_size = q.size(0)
q_eps = q_norm.variance_epsilon
k_eps = k_norm.variance_epsilon
# Only try fused path on CUDA and when it won't introduce implicit copies.
if (
_is_cuda
and allow_inplace
and (q_eps == k_eps)
and can_use_fused_inplace_qknorm(head_dim, q.dtype)
):
fused_inplace_qknorm(
q=q.view(batch_size, -1, head_dim),
k=k.view(batch_size, -1, head_dim),
q_weight=q_norm.weight,
k_weight=k_norm.weight,
head_dim=head_dim,
eps=q_eps,
)
return q, k
q_shape = q.shape
k_shape = k.shape
q_out = q_norm(q.view(-1, head_dim)).view(q_shape)
k_out = k_norm(k.view(-1, head_dim)).view(k_shape)
return q_out, k_out
def tensor_parallel_rms_norm(x: torch.Tensor, norm: "RMSNorm") -> torch.Tensor:
tp_rank = get_tensor_model_parallel_rank()
tp_size = get_tensor_model_parallel_world_size()
src_dtype = x.dtype
weight = norm.weight.tensor_split(tp_size)[tp_rank].float()
x_fp32 = x.float()
variance = x_fp32.pow(2).mean(dim=-1, keepdim=True)
variance = get_tp_group().all_reduce(
variance, op=torch._C._distributed_c10d.ReduceOp.AVG
)
output = x_fp32 * torch.rsqrt(variance + norm.variance_epsilon) * weight
return output.to(dtype=src_dtype)
# TODO: Workaround, fuse norm with new select01 kernel
def apply_layernorm_only(x: torch.Tensor, layernorm_scale_shift: LayerNormScaleShift):
return norm_infer(
x.view(-1, x.shape[-1]),
layernorm_scale_shift.norm.weight,
layernorm_scale_shift.norm.bias,
eps=layernorm_scale_shift.eps,
is_rms_norm=False,
).view(x.shape)