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# Copyright (c) 2023, Tri Dao.
""""
The implementation was adopted from
https://github.com/Dao-AILab/flash-attention/blob/43950dda456e095969d842fca7a73c5bfe3cecd0
"""
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.distributed import ProcessGroup
try:
from flash_attn.ops.activations import swiglu
except ImportError:
swiglu = None
try:
from flash_attn.ops.fused_dense import ColumnParallelLinear, RowParallelLinear
except ImportError:
ColumnParallelLinear, RowParallelLinear = None, None
try:
from flash_attn.ops.fused_dense import FusedMLP, ParallelFusedMLP
except ImportError:
FusedMLP, ParallelFusedMLP = None, None
class Mlp(nn.Module):
def __init__(
self,
in_features,
hidden_features=None,
out_features=None,
activation=F.gelu,
bias1=True,
bias2=True,
return_residual=False,
device=None,
dtype=None,
):
factory_kwargs = {"device": device, "dtype": dtype}
super().__init__()
out_features = out_features if out_features is not None else in_features
hidden_features = hidden_features if hidden_features is not None else in_features * 4
self.return_residual = return_residual
self.fc1 = nn.Linear(in_features, hidden_features, bias=bias1, **factory_kwargs)
self.activation = activation
self.fc2 = nn.Linear(hidden_features, out_features, bias=bias2, **factory_kwargs)
def forward(self, x):
y = self.fc1(x)
y = self.activation(y)
y = self.fc2(y)
return y if not self.return_residual else (y, x)
class ParallelMLP(nn.Module):
def __init__(
self,
in_features,
hidden_features=None,
out_features=None,
activation=F.gelu,
process_group: ProcessGroup = None,
sequence_parallel=True,
bias1=True,
bias2=True,
device=None,
dtype=None,
):
factory_kwargs = {"device": device, "dtype": dtype}
super().__init__()
assert ColumnParallelLinear is not None, "Need to install fused_dense"
assert RowParallelLinear is not None, "Need to install fused_dense"
out_features = out_features if out_features is not None else in_features
hidden_features = hidden_features if hidden_features is not None else in_features * 4
self.fc1 = ColumnParallelLinear(
in_features,
hidden_features,
process_group,
bias=bias1,
sequence_parallel=sequence_parallel,
**factory_kwargs,
)
self.activation = activation
self.fc2 = RowParallelLinear(
hidden_features,
out_features,
process_group,
bias=bias2,
sequence_parallel=sequence_parallel,
**factory_kwargs,
)
def forward(self, x):
y = self.fc1(x)
y = self.activation(y)
y = self.fc2(y)
return y
class GatedMlp(nn.Module):
def __init__(
self,
in_features,
hidden_features=None,
out_features=None,
activation=F.sigmoid,
bias1=True,
bias2=True,
multiple_of=128,
return_residual=False,
device=None,
dtype=None,
):
factory_kwargs = {"device": device, "dtype": dtype}
super().__init__()
out_features = out_features if out_features is not None else in_features
hidden_features = (
hidden_features if hidden_features is not None else int(8 * in_features / 3)
)
hidden_features = (hidden_features + multiple_of - 1) // multiple_of * multiple_of
self.return_residual = return_residual
self.fc1 = nn.Linear(in_features, 2 * hidden_features, bias=bias1, **factory_kwargs)
self.activation = activation
self.fc2 = nn.Linear(hidden_features, out_features, bias=bias2, **factory_kwargs)
def forward(self, x):
y = self.fc1(x)
if self.activation == F.sigmoid: # Special case for GLU
y = F.glu(y, dim=-1)
elif self.activation == F.silu and swiglu is not None: # Special case for SwiGLU
y, gate = y.chunk(2, dim=-1)
y = swiglu(gate, y)
else:
y, gate = y.chunk(2, dim=-1)
y = y * self.activation(gate)
y = self.fc2(y)
return y if not self.return_residual else (y, x)
class ParallelGatedMlp(nn.Module):
"""Parallel GatedMlp"""
def __init__(
self,
in_features,
process_group,
hidden_features=None,
out_features=None,
activation=F.sigmoid,
bias1=True,
bias2=True,
multiple_of=128,
sequence_parallel=True,
device=None,
dtype=None,
):
factory_kwargs = {"device": device, "dtype": dtype}
super().__init__()
out_features = out_features if out_features is not None else in_features
hidden_features = (
hidden_features if hidden_features is not None else int(8 * in_features / 3)
)
hidden_features = (hidden_features + multiple_of - 1) // multiple_of * multiple_of
if ColumnParallelLinear is None or RowParallelLinear is None:
raise ImportError("fused_dense is not installed")
self.fc1 = ColumnParallelLinear(
in_features,
2 * hidden_features,
process_group,
bias=bias1,
sequence_parallel=sequence_parallel,
**factory_kwargs,
)
self.activation = activation
self.fc2 = RowParallelLinear(
hidden_features,
out_features,
process_group,
bias=bias2,
sequence_parallel=sequence_parallel,
**factory_kwargs,
)
def forward(self, x):
y = self.fc1(x)
if self.activation == F.sigmoid: # Special case for GLU
y = F.glu(y, dim=-1)
else:
y, gate = y.chunk(2, dim=-1)
y = y * self.activation(gate)
y = self.fc2(y)
return y
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