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sglang/python/sglang/srt/layers/layernorm.py
2026-03-18 22:15:24 -07:00

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Python

# Copyright 2023-2024 SGLang Team
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Fused operators for normalization layers."""
import logging
from typing import Optional, Tuple, Union
import torch
import torch.nn as nn
import torch.nn.functional as F
from sglang.srt.batch_invariant_ops import (
is_batch_invariant_mode_enabled,
rms_norm_batch_invariant,
)
from sglang.srt.environ import envs
from sglang.srt.layers.utils import MultiPlatformOp
from sglang.srt.server_args import get_global_server_args
from sglang.srt.utils import (
cpu_has_amx_support,
get_bool_env_var,
is_cpu,
is_cuda,
is_flashinfer_available,
is_hip,
is_npu,
is_xpu,
)
_is_cuda = is_cuda()
_is_flashinfer_available = is_flashinfer_available()
_is_hip = is_hip()
_is_npu = is_npu()
_use_aiter = get_bool_env_var("SGLANG_USE_AITER") and _is_hip
_is_cpu_amx_available = cpu_has_amx_support()
_is_cpu = is_cpu()
_is_xpu = is_xpu()
_flashinfer_layernorm_available = False
if _is_cuda or _is_xpu:
if _is_flashinfer_available:
try:
from flashinfer.norm import layernorm
_flashinfer_layernorm_available = True
except (ImportError, AttributeError):
_flashinfer_layernorm_available = False
else:
_flashinfer_layernorm_available = False
from sgl_kernel import (
fused_add_rmsnorm,
gemma_fused_add_rmsnorm,
gemma_rmsnorm,
rmsnorm,
)
_has_vllm_rms_norm = False
if _use_aiter:
from aiter import rmsnorm2d_fwd as rms_norm
from aiter import rmsnorm2d_fwd_with_add as fused_add_rms_norm
_has_vllm_rms_norm = True # aiter provides the rms_norm functions
elif _is_hip:
try:
from vllm._custom_ops import fused_add_rms_norm, rms_norm
_has_vllm_rms_norm = True
except ImportError:
# Fallback: vllm not available, will use forward_native
_has_vllm_rms_norm = False
logger = logging.getLogger(__name__)
if _is_npu:
import torch_npu
def _forward_with_allreduce_fusion(
norm_module,
x: torch.Tensor,
residual: Optional[torch.Tensor],
post_residual_addition: Optional[torch.Tensor],
weight: torch.Tensor,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
"""Shared allreduce-fused RMSNorm logic usable by any norm."""
if residual is not None:
from sglang.srt.distributed import (
get_tensor_model_parallel_world_size,
tensor_model_parallel_all_reduce,
tensor_model_parallel_fused_allreduce_rmsnorm,
)
from sglang.srt.layers.flashinfer_comm_fusion import (
flashinfer_allreduce_residual_rmsnorm,
)
if get_tensor_model_parallel_world_size() > 1:
if post_residual_addition is not None:
residual = residual + post_residual_addition
# Prefer AITER fused AR+RMSNorm when enabled on AMD.
if _use_aiter:
fused_result = tensor_model_parallel_fused_allreduce_rmsnorm(
x, residual, weight, norm_module.variance_epsilon
)
if fused_result is not None:
return fused_result
else:
fused_result = flashinfer_allreduce_residual_rmsnorm(
input_tensor=x,
residual=residual,
weight=weight,
eps=norm_module.variance_epsilon,
)
if fused_result[0] is not None:
return fused_result
# For AITER route, preserve correctness when fused path is unavailable.
if _use_aiter and get_global_server_args().enable_aiter_allreduce_fusion:
x = tensor_model_parallel_all_reduce(x)
return norm_module.forward(x, residual, None)
return norm_module.forward(x, residual, post_residual_addition)
class RMSNorm(MultiPlatformOp):
def __init__(
self,
hidden_size: int,
eps: float = 1e-6,
var_hidden_size: Optional[int] = None,
cast_x_before_out_mul: bool = False,
fp32_residual: bool = False,
has_weight: bool = True,
weight_dtype: Optional = None,
override_orig_dtype: Optional = None,
) -> None:
super().__init__()
self.has_weight = has_weight
self.cast_x_before_out_mul = cast_x_before_out_mul
self.fp32_residual = fp32_residual
self.override_orig_dtype = override_orig_dtype
if self.has_weight:
self.weight = nn.Parameter(torch.ones(hidden_size, dtype=weight_dtype))
else:
self.weight = torch.ones(hidden_size, dtype=weight_dtype)
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 _use_aiter:
self._forward_method = self.forward_aiter
def forward_cuda(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if x.numel() == 0:
return x
if self.variance_size_override is not None:
return self.forward_native(x, residual, post_residual_addition)
if is_batch_invariant_mode_enabled():
if (
residual is not None
or get_global_server_args().rl_on_policy_target == "fsdp"
):
return self.forward_native(x, residual, post_residual_addition)
return rms_norm_batch_invariant(
x,
self.weight.data,
self.variance_epsilon,
)
if residual is not None:
# TODO: Ideally we want to have (hidden_states+residual)+post_residual_addition.
# but right now we can only have hidden_states+(residual+post_residual_addition).
# (hidden_states+residual)+post_residual_addition != hidden_states+(residual+post_residual_addition),
# we probably need to add another parameter to fused_add_rmsnorm
if post_residual_addition is not None:
residual = residual + post_residual_addition
fused_add_rmsnorm(x, residual, self.weight.data, self.variance_epsilon)
return x, residual
out = rmsnorm(x, self.weight.data, self.variance_epsilon)
return out
def forward_npu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
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_aiter(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if residual is not None:
residual_out = torch.empty_like(x)
output = torch.empty_like(x)
if post_residual_addition is not None:
residual = residual + post_residual_addition
fused_add_rms_norm(
output,
x,
residual,
residual_out,
self.weight.data,
self.variance_epsilon,
)
return output, residual_out
return rms_norm(x, self.weight.data, self.variance_epsilon)
def forward_hip(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
# Fallback to native implementation if vllm is not available
if not _has_vllm_rms_norm:
return self.forward_native(x, residual, post_residual_addition)
if not x.is_contiguous():
# NOTE: Remove this if aiter kernel supports discontinuous input
x = x.contiguous()
if residual is not None:
out = torch.empty_like(x)
residual_out = torch.empty_like(x)
if post_residual_addition is not None:
residual = residual + post_residual_addition
fused_add_rms_norm(
out, x, residual_out, residual, self.weight.data, self.variance_epsilon
)
return out, residual_out
out = torch.empty_like(x)
rms_norm(out, x, self.weight.data, self.variance_epsilon)
return out
def forward_native(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if not x.is_contiguous():
x = x.contiguous()
orig_dtype = self.override_orig_dtype or x.dtype
x = x.to(torch.float32)
if residual is not None:
x = x + residual.to(torch.float32)
if post_residual_addition is not None:
x = x + post_residual_addition.to(torch.float32)
if self.fp32_residual:
residual = x.clone()
else:
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)
if self.cast_x_before_out_mul:
x = self.weight * x.to(orig_dtype)
else:
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,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if _is_cpu_amx_available:
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
torch.ops.sgl_kernel.fused_add_rmsnorm_cpu(
x, residual, self.weight.data, self.variance_epsilon
)
return x, residual
return torch.ops.sgl_kernel.rmsnorm_cpu(
x, self.weight.data, self.variance_epsilon
)
else:
return self.forward_native(x, residual, post_residual_addition)
def forward_xpu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if self.variance_size_override is not None:
return self.forward_native(x, residual, post_residual_addition)
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
fused_add_rmsnorm(x, residual, self.weight.data, self.variance_epsilon)
return x, residual
out = rmsnorm(x, self.weight.data, self.variance_epsilon)
return out
def forward_with_allreduce_fusion(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
"""Forward with allreduce fusion, prioritizing flashinfer fused operations."""
return _forward_with_allreduce_fusion(
self, x, residual, post_residual_addition, self.weight
)
class LayerNorm(MultiPlatformOp):
def __init__(
self,
hidden_size: int,
eps: float = 1e-6,
elementwise_affine: bool = True,
bias: bool = True,
dtype: torch.dtype = torch.float32,
) -> None:
super().__init__()
self.hidden_size = hidden_size
self.variance_epsilon = eps
self.elementwise_affine = elementwise_affine
self.use_bias = bias
self.dtype = dtype
self.bias = nn.Parameter(torch.zeros(hidden_size, dtype=self.dtype))
self.weight = nn.Parameter(torch.ones(hidden_size, dtype=self.dtype))
def forward_cuda(
self,
x: torch.Tensor,
) -> torch.Tensor:
if (
_flashinfer_layernorm_available
and x.dtype == torch.bfloat16
and self.dtype == torch.float32
):
return layernorm(x, self.weight, self.bias, self.variance_epsilon)
else:
return self.forward_native(x)
def forward_native(
self,
x: torch.Tensor,
) -> torch.Tensor:
weight = self.weight if self.elementwise_affine else None
bias = self.bias if self.use_bias else None
orig_dtype = x.dtype
x = x.to(self.dtype)
return F.layer_norm(
x,
(self.hidden_size,),
weight=weight,
bias=bias,
eps=self.variance_epsilon,
).to(orig_dtype)
def forward_hip(
self,
x: torch.Tensor,
) -> torch.Tensor:
return self.forward_native(x)
def forward_npu(
self,
x: torch.Tensor,
) -> torch.Tensor:
return self.forward_native(x)
def forward_cpu(
self,
x: torch.Tensor,
) -> torch.Tensor:
if _is_cpu_amx_available:
bias_data = self.bias.data if self.use_bias else None
return torch.ops.sgl_kernel.layernorm_cpu(
x, self.weight.data, bias_data, self.variance_epsilon
)
else:
return self.forward_native(x)
class GemmaRMSNorm(MultiPlatformOp):
def __init__(
self,
hidden_size: int,
eps: float = 1e-6,
) -> None:
super().__init__()
self.weight = nn.Parameter(torch.zeros(hidden_size))
self.variance_epsilon = eps
# Re-dispatch
if _is_hip:
self._forward_method = self.forward_native
def _forward_impl(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
gemma_fused_add_rmsnorm(
x, residual, self.weight.data, self.variance_epsilon
)
return x, residual
out = gemma_rmsnorm(x, self.weight.data, self.variance_epsilon)
return out
def forward_native(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
orig_dtype = x.dtype
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
x = x + residual
residual = x
x = x.float()
variance = x.pow(2).mean(dim=-1, keepdim=True)
x = x * torch.rsqrt(variance + self.variance_epsilon)
x = x * (1.0 + self.weight.float())
x = x.to(orig_dtype)
return x if residual is None else (x, residual)
def forward_cuda(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
return self._forward_impl(x, residual, post_residual_addition)
def forward_cpu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if _is_cpu_amx_available:
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
torch.ops.sgl_kernel.gemma_fused_add_rmsnorm_cpu(
x, residual, self.weight.data, self.variance_epsilon
)
return x, residual
return torch.ops.sgl_kernel.gemma_rmsnorm_cpu(
x, self.weight.data, self.variance_epsilon
)
return self.forward_native(x, residual, post_residual_addition)
def forward_npu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
if envs.SGLANG_NPU_FORWARD_NATIVE_GEMMA_RMS_NORM.get():
return self.forward_native(x, residual)
if residual is not None:
if post_residual_addition is not None:
residual = residual + post_residual_addition
x = x + residual
residual = x
x, _ = torch_npu.npu_gemma_rms_norm(x, self.weight, self.variance_epsilon)
return x if residual is None else (x, residual)
def forward_xpu(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
return self._forward_impl(x, residual, post_residual_addition)
def forward_with_allreduce_fusion(
self,
x: torch.Tensor,
residual: Optional[torch.Tensor] = None,
post_residual_addition: Optional[torch.Tensor] = None,
) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
"""Forward with allreduce fusion; uses 1 + weight for fused kernels."""
# TODO(brayden): we can see if TRTLLM allreduce fusion can provide gemma-style norm
return _forward_with_allreduce_fusion(
self, x, residual, post_residual_addition, self.weight + 1.0
)
class Gemma3RMSNorm(MultiPlatformOp):
def __init__(self, dim: int, eps: float = 1e-6):
super().__init__()
self.eps = eps
self.weight = nn.Parameter(torch.zeros(dim))
# Re-dispatch
def _norm(self, x):
return x * torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + self.eps)
def forward_native(self, x):
output = self._norm(x.float())
# Llama does x.to(float16) * w whilst Gemma3 is (x * w).to(float16)
# See https://github.com/huggingface/transformers/pull/29402
output = output * (1.0 + self.weight.float())
return output.type_as(x)
def forward_cpu(self, x):
if _is_cpu_amx_available and x.stride(-1) == 1:
return torch.ops.sgl_kernel.gemma3_rmsnorm_cpu(x, self.weight, self.eps)
return self.forward_native(x)
def forward_cuda(self, x):
return self.forward_native(x)
def forward_npu(self, x):
output, _ = torch_npu.npu_gemma_rms_norm(x, self.weight, self.eps)
return output
def extra_repr(self):
return f"{tuple(self.weight.shape)}, eps={self.eps}"