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icefall/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py

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#!/usr/bin/env python3
# Copyright (c) 2021 University of Chinese Academy of Sciences (author: Han Zhu)
#
# See ../../../../LICENSE for clarification regarding multiple authors
#
# 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.
import copy
import math
import warnings
import itertools
from typing import List, Optional, Tuple, Union
import logging
import torch
import random
from encoder_interface import EncoderInterface
from scaling import (
Balancer,
BiasNorm,
Dropout2,
Dropout3,
SwooshL,
SwooshR,
ChunkCausalDepthwiseConv1d,
ActivationDropoutAndLinear,
ScaledConv1d,
ScaledConv2d,
ScaledLinear, # not as in other dirs.. just scales down initial parameter values.
Whiten,
Identity, # more friendly to backward hooks than nn.Identity(), for diagnostic reasons.
penalize_abs_values_gt,
softmax,
ScheduledFloat,
FloatLike,
limit_param_value,
convert_num_channels,
ScaleGrad,
)
from torch import Tensor, nn
from icefall.utils import make_pad_mask
from icefall.dist import get_rank
class Zipformer2(EncoderInterface):
"""
Args:
Note: all "int or Tuple[int]" arguments below will be treated as lists of the same length
as downsampling_factor if they are single ints or one-element tuples. The length of
downsampling_factor defines the number of stacks.
num_features (int): Number of input features, e.g. 40.
output_downsampling_factor (int): how much to downsample at the output. Note:
we also downsample by a factor of 2 in the Conv2dSubsampling encoder.
You should probably leave this at 2.
downsampling_factor (Tuple[int]): downsampling factor for each encoder stack.
Note: this is in addition to the downsampling factor of 2 that is applied in
the frontend (self.encoder_embed).
encoder_dim (Tuple[int]): embedding dimension of each of the encoder stacks, one per
encoder stack.
num_encoder_layers (int or Tuple[int])): number of encoder layers for each stack
encoder_unmasked_dim (int or Tuple[int]): unmasked dimension in each of
the encoder stacks for purposes of per-frame dropout (recommend 256 for
now).
query_head_dim (int or Tuple[int]): dimension of query and key per attention
head: per stack, if a tuple..
value_head_dim (int or Tuple[int]): dimension of value in each attention head
pos_head_dim (int or Tuple[int]): dimension of positional-encoding projection per
attention head
num_heads: (int or Tuple[int]): number of heads in the self-attention mechanism.
Must be at least 4.
feedforward_dim (int or Tuple[int]): hidden dimension in feedforward modules
cnn_module_kernel (int or Tuple[int])): Kernel size of convolution module
pos_dim (int): the dimension of each positional-encoding vector prior to projection,
e.g. 128.
dropout (float): dropout rate
warmup_batches (float): number of batches to warm up over; this controls
dropout of encoder layers.
causal (bool): if True, support chunkwise causal convolution. This should
not hurt WER as no modeling power is lost, but the convolution modules will be
slightly slower and use more memory. Enables use of the chunk_size and
left_context_chunks options in forward(), which simulates streaming
decoding.
chunk_size: (list of int): only set this to other than [-1] if causal;
the chunk size will be randomly chosen from this list. -1 means no chunking.
left_context_frames: (list of int): determines the number of left-
context chunks for causal training; will be rounded to a number of
chunks. Must not be less than cnn_module_kernel (after factoring in
rounding and downsampling); an error will be thrown if this is violated.
"""
def __init__(
self,
num_features: int,
output_downsampling_factor: int = 2,
downsampling_factor: Tuple[int] = (2, 4),
encoder_dim: Union[int, Tuple[int]] = 384,
num_encoder_layers: Union[int, Tuple[int]] = 4,
encoder_unmasked_dim: Union[int, Tuple[int]] = 256,
query_head_dim: Union[int, Tuple[int]] = 24,
pos_head_dim: Union[int, Tuple[int]] = 4,
value_head_dim: Union[int, Tuple[int]] = 12,
num_heads: Union[int, Tuple[int]] = 8,
feedforward_dim: Union[int, Tuple[int]] = 1536,
cnn_module_kernel: Union[int, Tuple[int]] = 31,
pos_dim: int = 192,
dropout: FloatLike = None, # see code below for default
warmup_batches: float = 4000.0,
causal: bool = False,
chunk_size: Tuple[int] = [-1],
left_context_frames: Tuple[int] = [-1],
) -> None:
super(Zipformer2, self).__init__()
if dropout is None:
dropout = ScheduledFloat((0.0, 0.3),
(20000.0, 0.1))
# this is not the probability of skipping a layer. It is the probability of
# dropping out the "skip module" which allows the model to skip groups of
# encoder stacks; when it's dropped out like this, it means we are forced
# to take the "direct" (non-bypass) path.
self.layer_skip_dropout_prob = ScheduledFloat((0.0, 0.5),
(warmup_batches, 0.025),
(20000.0, 0.0))
def _to_tuple(x):
""" Converts a single int or a 1-tuple of an int to a tuple with the same length
as downsampling_factor"""
if isinstance(x, int):
x = (x,)
if len(x) == 1:
x = x * len(downsampling_factor)
else:
assert len(x) == len(downsampling_factor) and isinstance(x[0], int)
return x
self.num_features = num_features # int
self.output_downsampling_factor = output_downsampling_factor # int
self.downsampling_factor = downsampling_factor # tuple
self.encoder_dim = encoder_dim = _to_tuple(encoder_dim) # tuple
self.encoder_unmasked_dim = encoder_unmasked_dim = _to_tuple(encoder_unmasked_dim) # tuple
num_encoder_layers = _to_tuple(num_encoder_layers)
query_head_dim = _to_tuple(query_head_dim)
value_head_dim = _to_tuple(value_head_dim)
pos_head_dim = _to_tuple(pos_head_dim)
num_heads = _to_tuple(num_heads)
feedforward_dim = _to_tuple(feedforward_dim)
self.cnn_module_kernel = cnn_module_kernel = _to_tuple(cnn_module_kernel)
self.causal = causal
self.chunk_size = chunk_size
self.left_context_frames = left_context_frames
for u,d in zip(encoder_unmasked_dim, encoder_dim):
assert u <= d
# self.encoder_embed converts the input of shape (N, T, num_features)
# to the shape (N, (T - 7) // 2, encoder_dims).
# That is, it does two things simultaneously:
# (1) subsampling: T -> (T - 7) // 2
# (2) embedding: num_features -> encoder_dims
# In the normal configuration, we will downsample once more at the end
# by a factor of 2, and most of the encoder stacks will run at a lower
# sampling rate.
self.encoder_embed = Conv2dSubsampling(num_features, encoder_dim[0],
dropout=dropout)
# each one will be Zipformer2Encoder or DownsampledZipformer2Encoder
encoders = []
num_encoders = len(downsampling_factor)
for i in range(num_encoders):
encoder_layer = Zipformer2EncoderLayer(
embed_dim=encoder_dim[i],
pos_dim=pos_dim,
num_heads=num_heads[i],
query_head_dim=query_head_dim[i],
pos_head_dim=pos_head_dim[i],
value_head_dim=value_head_dim[i],
feedforward_dim=feedforward_dim[i],
dropout=dropout,
cnn_module_kernel=cnn_module_kernel[i],
causal=causal,
)
# For the segment of the warmup period, we let the Conv2dSubsampling
# layer learn something. Then we start to warm up the other encoders.
encoder = Zipformer2Encoder(
encoder_layer,
num_encoder_layers[i],
pos_dim=pos_dim,
dropout=dropout,
warmup_begin=warmup_batches * (i + 1) / (num_encoders + 1),
warmup_end=warmup_batches * (i + 2) / (num_encoders + 1),
final_layerdrop_rate=0.035 * (downsampling_factor[i] ** 0.5),
)
if downsampling_factor[i] != 1:
encoder = DownsampledZipformer2Encoder(
encoder,
dim=encoder_dim[i],
downsample=downsampling_factor[i],
dropout=dropout,
)
# we are adding a new attribute here.
# this will be interpreted by get_named_parameter_groups_with_lrs().
encoder.lr_scale = downsampling_factor[i] ** -0.33
encoders.append(encoder)
self.encoders = nn.ModuleList(encoders)
# initializes self.skip_layers and self.skip_modules
self._init_skip_modules()
self.downsample_output = SimpleDownsample(max(encoder_dim),
downsample=output_downsampling_factor,
dropout=dropout)
def _init_skip_modules(self):
"""
If self.downampling_factor = (1, 2, 4, 8, 4, 2), then at the input of layer
indexed 4 (in zero indexing), with has subsapling_factor=4, we combine the output of
layers 2 and 3; and at the input of layer indexed 5, which which has subsampling_factor=2,
we combine the outputs of layers 1 and 5.
"""
skip_layers = []
skip_modules = []
z = self.downsampling_factor
for i in range(len(z)):
if i <= 1 or z[i-1] <= z[i]:
skip_layers.append(None)
skip_modules.append(Identity())
else:
# TEMP
for j in range(i-2, -1, -1):
if z[j] <= z[i] or j == 0:
# TEMP logging statement.
logging.info(f"At encoder stack {i}, which has downsampling_factor={z[i]}, we will "
f"combine the outputs of layers {j} and {i-1}, with downsampling_factor={z[j]} and {z[i-1]}.")
skip_layers.append(j)
skip_modules.append(BypassModule(self.encoder_dim[i]))
break
self.skip_layers = skip_layers
self.skip_modules = nn.ModuleList(skip_modules)
def get_feature_masks(
self,
x: torch.Tensor) -> List[Union[float, Tensor]]:
"""
In eval mode, returns [1.0] * num_encoders; in training mode, returns a number of
randomized feature masks, one per encoder.
On e.g. 15% of frames, these masks will zero out all enocder dims larger than
some supplied number, e.g. >256, so in effect on those frames we are using
a smaller encoer dim.
We generate the random masks at this level because we want the 2 masks to 'agree'
all the way up the encoder stack. This will mean that the 1st mask will have
mask values repeated self.zipformer_subsampling_factor times.
Args:
x: the embeddings (needed for the shape and dtype and device), of shape
(1, batch_size, encoder_dims0)
"""
num_encoders = len(self.encoder_dim)
if not self.training:
return [ 1.0 ] * num_encoders
(num_frames0, batch_size, _encoder_dims0) = x.shape
assert self.encoder_dim[0] == _encoder_dims0
feature_mask_dropout_prob = 0.125
# mask1 shape: (1, batch_size, 1)
mask1 = (torch.rand(1, batch_size, 1,
device=x.device) >
feature_mask_dropout_prob).to(x.dtype)
# mask2 has additional sequences masked, about twice the number.
mask2 = torch.logical_and(mask1,
(torch.rand(1, batch_size, 1,
device=x.device) >
feature_mask_dropout_prob).to(x.dtype))
# dim: (1, batch_size, 2)
mask = torch.cat((mask1, mask2), dim=-1)
feature_masks = []
for i in range(num_encoders):
channels = self.encoder_dim[i]
feature_mask = torch.ones(1, batch_size, channels,
dtype=x.dtype, device=x.device)
u1 = self.encoder_unmasked_dim[i]
u2 = u1 + (channels - u1) // 2
feature_mask[:, :, u1:u2] *= mask[..., 0:1]
feature_mask[:, :, u2:] *= mask[..., 1:2]
feature_masks.append(feature_mask)
return feature_masks
def get_chunk_info(self) -> Tuple[int, int]:
"""
Returns chunk_size and left_context_chunks.
"""
if not self.causal:
return -1, -1
chunk_size = random.choice(self.chunk_size)
if chunk_size == -1:
left_context_chunks = -1
else:
left_context_frames = random.choice(self.left_context_frames)
# Note: in Python, -1 // n == -1 for n > 0
left_context_chunks = left_context_frames // chunk_size
if left_context_chunks == 0:
left_context_chunks = 1
return chunk_size, left_context_chunks
def forward(
self, x: torch.Tensor, x_lens: torch.Tensor,
) -> Tuple[torch.Tensor, torch.Tensor]:
"""
Args:
x:
The input tensor. Its shape is (batch_size, seq_len, feature_dim).
x_lens:
A tensor of shape (batch_size,) containing the number of frames in
`x` before padding.
chunk_size: Number of frames per chunk (only set this if causal == True).
Must divide all elements of downsampling_factor. At 50hz frame
rate, i.e. after encoder_embed. If not specified, no chunking.
left_context_chunks: Number of left-context chunks for each chunk (affects
attention mask); only set this if chunk_size specified. If -1, there
is no limit on the left context. If not -1, require:
left_context_chunks * context_size >= downsampling_factor[i] *
cnn_module_kernel[i] // 2.
Returns:
Return a tuple containing 2 tensors:
- embeddings: its shape is (batch_size, output_seq_len, max(encoder_dim))
- lengths, a tensor of shape (batch_size,) containing the number
of frames in `embeddings` before padding.
"""
# logging.info(f"Memory allocated at entry: {torch.cuda.memory_allocated() // 1000000}M")
x = self.encoder_embed(x)
# logging.info(f"Memory allocated after encoder_embed: {torch.cuda.memory_allocated() // 1000000}M")
x = x.permute(1, 0, 2) # (N, T, C) -> (T, N, C)
with warnings.catch_warnings():
warnings.simplefilter("ignore")
lengths = (x_lens - 7) // 2
assert x.size(0) == lengths.max().item()
src_key_padding_mask = make_pad_mask(lengths)
outputs = []
feature_masks = self.get_feature_masks(x)
chunk_size, left_context_chunks = self.get_chunk_info()
attn_mask = self._get_attn_mask(x, chunk_size, left_context_chunks)
for i, module in enumerate(self.encoders):
ds = self.downsampling_factor[i]
x = convert_num_channels(x, self.encoder_dim[i])
if self.skip_layers[i] is not None:
# this how we implement U-net-like skipping of some series of
# stacks. The layer_skip_dropout_prob is to discourage it from
# completely ignoring the middle layers, especially early in
# training,
skip_output = convert_num_channels(outputs[self.skip_layers[i]],
self.encoder_dim[i])
skip_x = self.skip_modules[i](skip_output, x)
layer_skip_dropout_prob = float(self.layer_skip_dropout_prob)
if self.training and layer_skip_dropout_prob > 0:
batch_size = x.shape[1]
mask = (torch.rand((1, batch_size, 1), device=x.device) >
layer_skip_dropout_prob)
x = torch.where(mask, skip_x, x)
else:
x = skip_x
x = module(x,
chunk_size=chunk_size,
feature_mask=feature_masks[i],
src_key_padding_mask=(None if src_key_padding_mask is None
else src_key_padding_mask[...,::ds]),
attn_mask=attn_mask,
)
outputs.append(x)
def get_full_dim_output():
num_encoders = len(self.encoder_dim)
assert len(outputs) == num_encoders
output_dim = max(self.encoder_dim)
output_pieces = [ outputs[-1] ]
cur_dim = self.encoder_dim[-1]
for i in range(num_encoders - 2, -1, -1):
d = self.encoder_dim[i]
if d > cur_dim:
this_output = outputs[i]
output_pieces.append(this_output[..., cur_dim:d])
cur_dim = d
assert cur_dim == output_dim
return torch.cat(output_pieces, dim=-1)
# if the last output has the largest dimension, x will be unchanged,
# it will be the same as outputs[-1]. Otherwise it will be concatenated
# from different pieces of 'outputs', taking each dimension from the
# most recent output that has it present.
x = get_full_dim_output()
x = self.downsample_output(x)
# class Downsample has this rounding behavior..
assert self.output_downsampling_factor == 2
with warnings.catch_warnings():
warnings.simplefilter("ignore")
lengths = (lengths + 1) // 2
x = x.permute(1, 0, 2) # (T, N, C) ->(N, T, C)
return x, lengths
def _get_attn_mask(self, x: Tensor,
chunk_size: int,
left_context_chunks: int
) -> Optional[Tensor]:
"""
Return None if chunk_size == -1, else return attention mask of shape
(seq_len, seq_len), interpreted as (tgt_seq_len, src_seq_len). True
means a masked position.
Args:
x: embeddings after self.encoder_embed(), of shape (seq_len, batch_size, embed_dim).
chunk_size: chunk size, must divide
"""
if chunk_size <= 0:
return None
assert all(chunk_size % d == 0 for d in self.downsampling_factor)
if left_context_chunks >= 0:
num_encoders = len(self.encoder_dim)
assert all (chunk_size * left_context_chunks >=
(self.cnn_module_kernel[i] // 2) * self.downsampling_factor[i]
for i in range(num_encoders))
else:
left_context_chunks = 1000000
seq_len = x.shape[0]
# t is frame index, shape (seq_len,)
t = torch.arange(seq_len, dtype=torch.int32, device=x.device)
# c is chunk index for each frame, shape (seq_len,)
c = t // chunk_size
src_c = c
tgt_c = c.unsqueeze(-1)
attn_mask = torch.logical_or(src_c > tgt_c,
src_c < tgt_c - left_context_chunks)
if __name__ == "__main__":
logging.info(f"attn_mask = {attn_mask}")
return attn_mask
def _whitening_schedule(x: float, ratio: float = 2.0) -> ScheduledFloat:
return ScheduledFloat((0.0, x),
(20000.0, ratio * x),
default=x)
def _balancer_schedule(min_prob: float):
return ScheduledFloat((0.0, 0.4), (8000.0, min_prob))
class Zipformer2EncoderLayer(nn.Module):
"""
Args:
embed_dim: the number of expected features in the input (required).
nhead: the number of heads in the multiheadattention models (required).
feedforward_dim: the dimension of the feedforward network model (default=2048).
dropout: the dropout value (default=0.1).
cnn_module_kernel (int): Kernel size of convolution module.
Examples::
>>> encoder_layer = Zipformer2EncoderLayer(embed_dim=512, nhead=8)
>>> src = torch.rand(10, 32, 512)
>>> pos_emb = torch.rand(32, 19, 512)
>>> out = encoder_layer(src, pos_emb)
"""
def __init__(
self,
embed_dim: int,
pos_dim: int,
num_heads: int,
query_head_dim: int,
pos_head_dim: int,
value_head_dim: int,
feedforward_dim: int,
dropout: FloatLike = 0.1,
cnn_module_kernel: int = 31,
causal: bool = False,
attention_skip_rate: FloatLike = ScheduledFloat((0.0, 0.2), (4000.0, 0.05), (16000, 0.0), default=0),
conv_skip_rate: FloatLike = ScheduledFloat((0.0, 0.2), (4000.0, 0.05), (16000, 0.0), default=0),
const_attention_rate: FloatLike = ScheduledFloat((0.0, 0.25), (4000.0, 0.025), default=0),
ff2_skip_rate: FloatLike = ScheduledFloat((0.0, 0.1), (4000.0, 0.01), (50000.0, 0.0)),
ff3_skip_rate: FloatLike = ScheduledFloat((0.0, 0.1), (4000.0, 0.01), (50000.0, 0.0)),
bypass_skip_rate: FloatLike = ScheduledFloat((0.0, 0.5), (4000.0, 0.02), default=0),
) -> None:
super(Zipformer2EncoderLayer, self).__init__()
self.embed_dim = embed_dim
# self.bypass implements layer skipping as well as bypass; see its default values.
self.bypass = BypassModule(embed_dim, skip_rate=bypass_skip_rate)
# bypass_mid is bypass used in the middle of the layer.
self.bypass_mid = BypassModule(embed_dim)
# skip probability for dynamic modules (meaning: anything but feedforward).
self.attention_skip_rate = copy.deepcopy(attention_skip_rate)
# an additional skip probability that applies to ConvModule to stop it from
# contributing too much early on.
self.conv_skip_rate = copy.deepcopy(conv_skip_rate)
# ff2_skip_rate is to prevent the ff2 module from having output that's too big
# compared to its residual.
self.ff2_skip_rate = copy.deepcopy(ff2_skip_rate)
self.ff3_skip_rate = copy.deepcopy(ff3_skip_rate)
self.const_attention_rate = copy.deepcopy(const_attention_rate)
self.self_attn_weights = RelPositionMultiheadAttentionWeights(
embed_dim, pos_dim=pos_dim, num_heads=num_heads,
query_head_dim=query_head_dim, pos_head_dim=pos_head_dim,
dropout=0.0,
)
self.self_attn1 = SelfAttention(embed_dim, num_heads,
value_head_dim)
self.self_attn2 = SelfAttention(embed_dim, num_heads,
value_head_dim)
self.feed_forward1 = FeedforwardModule(embed_dim,
(feedforward_dim * 3) // 4,
dropout)
self.feed_forward2 = FeedforwardModule(embed_dim,
feedforward_dim,
dropout)
self.feed_forward3 = FeedforwardModule(embed_dim,
(feedforward_dim * 5) // 4,
dropout)
self.nonlin_attention = NonlinAttention(embed_dim,
hidden_channels=3 * embed_dim // 4)
self.conv_module1 = ConvolutionModule(embed_dim,
cnn_module_kernel,
causal=causal)
self.conv_module2 = ConvolutionModule(embed_dim,
cnn_module_kernel,
causal=causal)
#self.attention_squeeze = AttentionSqueeze(embed_dim, embed_dim // 2)
self.norm = BiasNorm(embed_dim)
self.bypass_scale = nn.Parameter(torch.full((embed_dim,), 0.5))
self.balancer1 = Balancer(
embed_dim, channel_dim=-1,
min_positive=0.45, max_positive=0.55,
min_abs=0.2, max_abs=4.0,
)
# balancer for output of NonlinAttentionModule
self.balancer_na = Balancer(
embed_dim, channel_dim=-1,
min_positive=0.3, max_positive=0.7,
min_abs=ScheduledFloat((0.0, 0.004), (4000.0, 0.02)),
prob=0.05, # out of concern for memory usage
)
# balancer for output of feedforward2, prevent it from staying too
# small. give this a very small probability, even at the start of
# training, it's to fix a rare problem and it's OK to fix it slowly.
self.balancer_ff2 = Balancer(
embed_dim, channel_dim=-1,
min_positive=0.3, max_positive=0.7,
min_abs=ScheduledFloat((0.0, 0.0), (4000.0, 0.1), default=0.0),
max_abs=2.0,
prob=0.05,
)
self.balancer_ff3 = Balancer(
embed_dim, channel_dim=-1,
min_positive=0.3, max_positive=0.7,
min_abs=ScheduledFloat((0.0, 0.0), (4000.0, 0.2), default=0.0),
max_abs=4.0,
prob=0.05,
)
self.whiten = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(4.0, ratio=3.0),
prob=(0.025, 0.25),
grad_scale=0.01)
self.balancer2 = Balancer(
embed_dim, channel_dim=-1,
min_positive=0.45, max_positive=0.55,
min_abs=0.1, max_abs=4.0,
)
def get_bypass_scale(self, batch_size: int):
# returns bypass-scale of shape (num_channels,),
# or (batch_size, num_channels,). This is actually the
# scale on the non-residual term, so 0 correponds to bypassing
# this module.
if torch.jit.is_scripting() or not self.training:
return self.bypass_scale
else:
ans = limit_param_value(self.bypass_scale,
min=float(self.bypass_min),
max=float(self.bypass_max))
layer_skip_rate = float(self.layer_skip_rate)
if layer_skip_rate != 0.0:
mask = torch.rand((batch_size, 1), device=ans.device) > layer_skip_rate
ans = ans * mask
# now ans is of shape (batch_size, num_channels), and is zero for sequences
# on which we have randomly chosen to do layer-skipping.
return ans
def get_sequence_dropout_mask(self, x: Tensor, dropout_rate: float) -> Optional[Tensor]:
if dropout_rate == 0.0 or not self.training or torch.jit.is_scripting():
return None
batch_size = x.shape[1]
mask = (torch.rand(batch_size, 1, device=x.device) > dropout_rate).to(x.dtype)
return mask
def sequence_dropout(self, x: Tensor, dropout_rate: float) -> Tensor:
"""
Apply sequence-level dropout to x.
x shape: (seq_len, batch_size, embed_dim)
"""
dropout_mask = self.get_sequence_dropout_mask(x, dropout_rate)
if dropout_mask is None:
return x
else:
return x * dropout_mask
def forward(
self,
src: Tensor,
pos_emb: Tensor,
chunk_size: int = -1,
attn_mask: Optional[Tensor] = None,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tensor:
"""
Pass the input through the encoder layer.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
pos_emb: (1, 2*seq_len-1, pos_emb_dim) or (batch_size, 2*seq_len-1, pos_emb_dim)
chunk_size: the number of frames per chunk, of >= 0; if -1, no chunking.
feature_mask: something that broadcasts with src, that we'll multiply `src`
by at every layer: if a Tensor, likely of shape (seq_len, batch_size, embedding_dim)
attn_mask: the attention mask, of shape (batch_size, seq_len, seq_len) or (seq_len, seq_len),
interpreted as (batch_size, tgt_seq_len, src_seq_len) or (tgt_seq_len, src_seq_len).
True means masked position. May be None.
src_key_padding_mask: the mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns:
A tensor which has the same shape as src
"""
src_orig = src
# dropout rate for non-feedforward submodules
attention_skip_rate = float(self.attention_skip_rate) if self.training else 0.0
# attn_weights: (num_heads, batch_size, seq_len, seq_len)
attn_weights = self.self_attn_weights(
src,
pos_emb=pos_emb,
attn_mask=attn_mask,
key_padding_mask=src_key_padding_mask,
)
self_attn_dropout_mask = self.get_sequence_dropout_mask(src, attention_skip_rate)
if True:
selected_attn_weights = attn_weights[0:2]
if random.random() < float(self.const_attention_rate):
# Make attention weights constant. The intention is to
# encourage these modules to do something similar to an
# averaging-over-time operation.
# only need the mask, can just use the 1st one and expand later
selected_attn_weights = selected_attn_weights[0:1]
selected_attn_weights = (selected_attn_weights > 0.0).to(selected_attn_weights.dtype)
selected_attn_weights = selected_attn_weights * (1.0 / selected_attn_weights.sum(dim=-1, keepdim=True))
selected_attn_weights = selected_attn_weights.expand(2, -1, -1, -1)
na = self.balancer_na(self.nonlin_attention(src,
selected_attn_weights[0:1]))
src = src + (na if self_attn_dropout_mask is None else na * self_attn_dropout_mask)
src = src + self.feed_forward1(src)
self_attn = self.self_attn1(
src, attn_weights)
src = src + (self_attn if self_attn_dropout_mask is None else self_attn * self_attn_dropout_mask)
src = src + self.sequence_dropout(self.conv_module1(src, chunk_size=chunk_size,
src_key_padding_mask=src_key_padding_mask),
float(self.conv_skip_rate))
src = src + self.sequence_dropout(self.balancer_ff2(self.feed_forward2(src)),
float(self.ff2_skip_rate))
# bypass in the middle of the layer.
src = self.bypass_mid(src_orig, src)
self_attn = self.self_attn2(
src, attn_weights)
src = src + (self_attn if self_attn_dropout_mask is None else self_attn * self_attn_dropout_mask)
src = src + self.sequence_dropout(self.conv_module2(src, chunk_size=chunk_size,
src_key_padding_mask=src_key_padding_mask),
float(self.conv_skip_rate))
src = src + self.sequence_dropout(self.balancer_ff3(self.feed_forward3(src)),
float(self.ff3_skip_rate))
src = self.balancer1(src)
src = self.norm(src)
src = self.bypass(src_orig, src)
src = self.balancer2(src)
src = self.whiten(src)
return src
class Zipformer2Encoder(nn.Module):
r"""Zipformer2Encoder is a stack of N encoder layers
Args:
encoder_layer: an instance of the Zipformer2EncoderLayer() class (required).
num_layers: the number of sub-encoder-layers in the encoder (required).
pos_dim: the dimension for the relative positional encoding
Examples::
>>> encoder_layer = Zipformer2EncoderLayer(embed_dim=512, nhead=8)
>>> zipformer_encoder = Zipformer2Encoder(encoder_layer, num_layers=6)
>>> src = torch.rand(10, 32, 512)
>>> out = zipformer_encoder(src)
"""
def __init__(
self,
encoder_layer: nn.Module,
num_layers: int,
pos_dim: int,
dropout: float,
warmup_begin: float,
warmup_end: float,
initial_layerdrop_rate: float = 0.5,
final_layerdrop_rate: float = 0.05,
) -> None:
super().__init__()
self.encoder_pos = CompactRelPositionalEncoding(pos_dim, dropout_rate=0.15,
length_factor=3.0)
self.layers = nn.ModuleList(
[copy.deepcopy(encoder_layer) for i in range(num_layers)]
)
self.num_layers = num_layers
assert 0 <= warmup_begin <= warmup_end
delta = (1. / num_layers) * (warmup_end - warmup_begin)
cur_begin = warmup_begin # interpreted as a training batch index
for i in range(num_layers):
cur_end = cur_begin + delta
self.layers[i].bypass.skip_rate = ScheduledFloat((cur_begin, initial_layerdrop_rate),
(cur_end, final_layerdrop_rate),
default=0.0)
cur_begin = cur_end
def forward(
self,
src: Tensor,
chunk_size: int = -1,
feature_mask: Union[Tensor, float] = 1.0,
attn_mask: Optional[Tensor] = None,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tensor:
r"""Pass the input through the encoder layers in turn.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
chunk_size: the number of frames per chunk, of >= 0; if -1, no chunking.
feature_mask: something that broadcasts with src, that we'll multiply `src`
by at every layer: if a Tensor, likely of shape (seq_len, batch_size, embedding_dim)
attn_mask: the attention mask, of shape (batch_size, seq_len, seq_len) or (seq_len, seq_len),
interpreted as (batch_size, tgt_seq_len, src_seq_len) or (tgt_seq_len, src_seq_len).
True means masked position. May be None.
src_key_padding_mask: the mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns: a Tensor with the same shape as src.
"""
pos_emb = self.encoder_pos(src)
output = src
rnd_seed = src.numel() + random.randint(0, 1000)
output = output * feature_mask
for i, mod in enumerate(self.layers):
output = mod(
output,
pos_emb,
chunk_size=chunk_size,
attn_mask=attn_mask,
src_key_padding_mask=src_key_padding_mask,
)
output = output * feature_mask
return output
class BypassModule(nn.Module):
"""
An nn.Module that implements a learnable bypass scale, and also randomized per-sequence
layer-skipping. The bypass is limited during early stages of training to be close to
"straight-through", i.e. to not do the bypass operation much initially, in order to
force all the modules to learn something.
"""
def __init__(
self,
embed_dim: int,
skip_rate: FloatLike = 0.0,
scale_min: FloatLike = ScheduledFloat((0.0, 0.9), (20000.0, 0.2), default=0),
scale_max: FloatLike = 1.0):
super().__init__()
self.bypass_scale = nn.Parameter(torch.full((embed_dim,), 0.5))
self.skip_rate = copy.deepcopy(skip_rate)
self.scale_min = copy.deepcopy(scale_min)
self.scale_max = copy.deepcopy(scale_max)
def _get_bypass_scale(self, batch_size: int):
# returns bypass-scale of shape (num_channels,),
# or (batch_size, num_channels,). This is actually the
# scale on the non-residual term, so 0 correponds to bypassing
# this module.
if torch.jit.is_scripting() or not self.training:
return self.bypass_scale
else:
ans = limit_param_value(self.bypass_scale,
min=float(self.scale_min),
max=float(self.scale_max))
skip_rate = float(self.skip_rate)
if skip_rate != 0.0:
mask = torch.rand((batch_size, 1), device=ans.device) > skip_rate
ans = ans * mask
# now ans is of shape (batch_size, num_channels), and is zero for sequences
# on which we have randomly chosen to do layer-skipping.
return ans
def forward(self,
src_orig: Tensor,
src: Tensor):
"""
Args: src_orig and src are both of shape (seq_len, batch_size, num_channels)
Returns: something with the same shape as src and src_orig
"""
bypass_scale = self._get_bypass_scale(src.shape[1])
return src_orig + (src - src_orig) * bypass_scale
class DownsampledZipformer2Encoder(nn.Module):
r"""
DownsampledZipformer2Encoder is a zipformer encoder evaluated at a reduced frame rate,
after convolutional downsampling, and then upsampled again at the output, and combined
with the origin input, so that the output has the same shape as the input.
"""
def __init__(self,
encoder: nn.Module,
dim: int,
downsample: int,
dropout: FloatLike):
super(DownsampledZipformer2Encoder, self).__init__()
self.downsample_factor = downsample
self.downsample = SimpleDownsample(dim,
downsample, dropout)
self.encoder = encoder
self.upsample = SimpleUpsample(dim, downsample)
self.out_combiner = BypassModule(dim)
def forward(self,
src: Tensor,
chunk_size: int = -1,
feature_mask: Union[Tensor, float] = 1.0,
attn_mask: Optional[Tensor] = None,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tuple[Tensor, Tensor]:
r"""Downsample, go through encoder, upsample.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
feature_mask: something that broadcasts with src, that we'll multiply `src`
by at every layer: if a Tensor, likely of shape (seq_len, batch_size, embedding_dim)
attn_mask: the attention mask, of shape (batch_size, seq_len, seq_len) or (seq_len, seq_len),
interpreted as (batch_size, tgt_seq_len, src_seq_len) or (tgt_seq_len, src_seq_len).
True means masked position. May be None.
src_key_padding_mask: the mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns: a Tensor with the same shape as src.
"""
src_orig = src
src = self.downsample(src)
ds = self.downsample_factor
if attn_mask is not None:
attn_mask = attn_mask[::ds,::ds]
src = self.encoder(
src,
chunk_size=chunk_size // ds,
feature_mask=feature_mask,
attn_mask=attn_mask,
src_key_padding_mask=src_key_padding_mask,
)
src = self.upsample(src)
# remove any extra frames that are not a multiple of downsample_factor
src = src[:src_orig.shape[0]]
return self.out_combiner(src_orig, src)
class SimpleDownsample(torch.nn.Module):
"""
Does downsampling with attention, by weighted sum, and a projection..
"""
def __init__(self,
channels: int,
downsample: int,
dropout: FloatLike):
super(SimpleDownsample, self).__init__()
self.bias = nn.Parameter(torch.zeros(downsample))
self.name = None # will be set from training code
self.dropout = copy.deepcopy(dropout)
self.downsample = downsample
def forward(self,
src: Tensor) -> Tensor:
"""
x: (seq_len, batch_size, in_channels)
Returns a tensor of shape
( (seq_len+downsample-1)//downsample, batch_size, channels)
"""
(seq_len, batch_size, in_channels) = src.shape
ds = self.downsample
d_seq_len = (seq_len + ds - 1) // ds
# Pad to an exact multiple of self.downsample
if seq_len != d_seq_len * ds:
# right-pad src, repeating the last element.
pad = d_seq_len * ds - seq_len
src_extra = src[src.shape[0]-1:].expand(pad, src.shape[1], src.shape[2])
src = torch.cat((src, src_extra), dim=0)
assert src.shape[0] == d_seq_len * ds
src = src.reshape(d_seq_len, ds, batch_size, in_channels)
weights = self.bias.softmax(dim=0)
# weights: (downsample, 1, 1)
weights = weights.unsqueeze(-1).unsqueeze(-1)
# ans1 is the first `in_channels` channels of the output
ans = (src * weights).sum(dim=1)
return ans
class SimpleUpsample(torch.nn.Module):
"""
A very simple form of upsampling that mostly just repeats the input, but
also adds a position-specific bias.
"""
def __init__(self,
num_channels: int,
upsample: int):
super(SimpleUpsample, self).__init__()
self.upsample = upsample
def forward(self,
src: Tensor) -> Tensor:
"""
x: (seq_len, batch_size, num_channels)
Returns a tensor of shape
( (seq_len*upsample), batch_size, num_channels)
"""
upsample = self.upsample
(seq_len, batch_size, num_channels) = src.shape
src = src.unsqueeze(1).expand(seq_len, upsample, batch_size, num_channels)
src = src.reshape(seq_len * upsample, batch_size, num_channels)
return src
class CompactRelPositionalEncoding(torch.nn.Module):
"""
Relative positional encoding module. This version is "compact" meaning it is able to encode
the important information about the relative position in a relatively small number of dimensions.
The goal is to make it so that small differences between large relative offsets (e.g. 1000 vs. 1001)
make very little difference to the embedding. Such differences were potentially important
when encoding absolute position, but not important when encoding relative position because there
is now no need to compare two large offsets with each other.
Our embedding works done by projecting the interval [-infinity,infinity] to a finite interval
using the atan() function, before doing the fourier transform of that fixed interval. The
atan() function would compress the "long tails" too small,
making it hard to distinguish between different magnitudes of large offsets, so we use a logarithmic
function to compress large offsets to a smaller range before applying atan().
Scalings are chosen in such a way that the embedding can clearly distinguish invidual offsets as long
as they are quite close to the origin, e.g. abs(offset) <= about sqrt(embedding_dim)
Args:
embed_dim: Embedding dimension.
dropout_rate: Dropout rate.
max_len: Maximum input length: just a heuristic for initialization.
length_factor: a heuristic scale (should be >= 1.0) which, if larger, gives
less weight to small differences of offset near the origin.
"""
def __init__(
self, embed_dim: int,
dropout_rate: FloatLike,
max_len: int = 1000,
length_factor: float = 1.0,
) -> None:
"""Construct a CompactRelPositionalEncoding object."""
super(CompactRelPositionalEncoding, self).__init__()
self.embed_dim = embed_dim
assert embed_dim % 2 == 0
self.dropout = Dropout2(dropout_rate)
self.pe = None
assert length_factor >= 1.0
self.length_factor = length_factor
self.extend_pe(torch.tensor(0.0).expand(max_len))
def extend_pe(self, x: Tensor) -> None:
"""Reset the positional encodings."""
if self.pe is not None:
# self.pe contains both positive and negative parts
# the length of self.pe is 2 * input_len - 1
if self.pe.size(0) >= x.size(0) * 2 - 1:
# Note: TorchScript doesn't implement operator== for torch.Device
if self.pe.dtype != x.dtype or str(self.pe.device) != str(
x.device
):
self.pe = self.pe.to(dtype=x.dtype, device=x.device)
return
T = x.size(0)
# if T == 4, x would contain [ -3, -2, 1, 0, 1, 2, 3 ]
x = torch.arange(-(T-1), T,
device=x.device).to(torch.float32).unsqueeze(1)
freqs = 1 + torch.arange(self.embed_dim // 2, device=x.device)
# `compression_length` this is arbitrary/heuristic, if it is larger we have more resolution
# for small time offsets but less resolution for large time offsets.
compression_length = (self.embed_dim ** 0.5)
# x_compressed, like X, goes from -infinity to infinity as T goes from -infinity to infinity;
# but it does so more slowly than T for large absolute values of T.
# The formula is chosen so that d(x_compressed )/dx is 1 around x == 0, which
# is important.
x_compressed = compression_length * x.sign() * ((x.abs() + compression_length).log() - math.log(compression_length))
# if self.length_factor == 1.0, then length_scale is chosen so that the
# FFT can exactly separate points close to the origin (T == 0). So this
# part of the formulation is not really heuristic.
# But empirically, for ASR at least, length_factor > 1.0 seems to work better.
length_scale = self.length_factor * self.embed_dim / (2.0 * math.pi)
# note for machine implementations: if atan is not available, we can use:
# x.sign() * ((1 / (x.abs() + 1)) - 1) * (-math.pi/2)
# check on wolframalpha.com: plot(sign(x) * (1 / ( abs(x) + 1) - 1 ) * -pi/2 , atan(x))
x_atan = (x_compressed / length_scale).atan() # results between -pi and pi
cosines = (x_atan * freqs).cos()
sines = (x_atan * freqs).sin()
pe = torch.zeros(x.shape[0], self.embed_dim, device=x.device)
pe[:, 0::2] = cosines
pe[:, 1::2] = sines
pe[:, -1] = 1.0 # for bias.
self.pe = pe.to(dtype=x.dtype)
def forward(self, x: torch.Tensor) -> Tensor:
"""Create positional encoding.
Args:
x (torch.Tensor): Input tensor (time, batch, `*`).
Returns:
positional embedding, of shape (1, 2*time-1, `*`).
"""
self.extend_pe(x)
pos_emb = self.pe[
self.pe.size(0) // 2
- x.size(0)
+ 1 : self.pe.size(0) // 2 # noqa E203
+ x.size(0),
:
]
pos_emb = pos_emb.unsqueeze(0)
return self.dropout(pos_emb)
class RelPositionMultiheadAttentionWeights(nn.Module):
r"""Module that computes multi-head attention weights with relative position encoding.
Various other modules consume the resulting attention weights: see, for example, the
SimpleAttention module which allows you to compute conventional attention.
This is a quite heavily modified from: "Transformer-XL: Attentive Language Models Beyond a Fixed-Length Context",
we have to write up the differences.
Args:
embed_dim: number of channels at the input to this module, e.g. 256
pos_dim: dimension of the positional encoding vectors, e.g. 128.
num_heads: number of heads to compute weights for, e.g. 8
query_head_dim: dimension of the query (and key), per head. e.g. 24.
pos_head_dim: dimension of the projected positional encoding per head, e.g. 4.
dropout: dropout probability for attn_output_weights. Default: 0.0.
pos_emb_skip_rate: probability for skipping the pos_emb part of the scores on
any given call to forward(), in training time.
"""
def __init__(
self,
embed_dim: int,
pos_dim: int,
num_heads: int,
query_head_dim: int,
pos_head_dim: int,
dropout: float = 0.0,
pos_emb_skip_rate: FloatLike = ScheduledFloat((0.0, 0.5),
(4000.0, 0.0))
) -> None:
super().__init__()
self.lr_scale = 0.9
self.embed_dim = embed_dim
self.num_heads = num_heads
self.query_head_dim = query_head_dim
self.pos_head_dim = pos_head_dim
self.dropout = dropout
self.pos_emb_skip_rate = copy.deepcopy(pos_emb_skip_rate)
self.name = None # will be overwritten in training code; for diagnostics.
key_head_dim = query_head_dim
in_proj_dim = (query_head_dim + key_head_dim + pos_head_dim) * num_heads
# the initial_scale is supposed to take over the "scaling" factor of
# head_dim ** -0.5 that has been used in previous forms of attention,
# dividing it between the query and key. Note: this module is intended
# to be used with the ScaledAdam optimizer; with most other optimizers,
# it would be necessary to apply the scaling factor in the forward function.
self.in_proj = ScaledLinear(embed_dim, in_proj_dim, bias=True,
initial_scale=query_head_dim**-0.25)
self.whiten_keys = Whiten(num_groups=num_heads,
whitening_limit=_whitening_schedule(3.0),
prob=(0.025, 0.25),
grad_scale=0.025)
# add a balancer for the keys that runs with very small probability, and
# tries to enforce that all dimensions have mean around zero. The
# weights produced by this module are invariant to adding a constant to
# the keys, so the derivative of the bias is mathematically zero; but
# due to how Adam/ScaledAdam work, it can learn a fairly large nonzero
# bias because the small numerical roundoff tends to have a non-random
# sign. This module is intended to prevent that. Use a very small
# probability; that should be suffixient to fix the problem.
self.balance_keys = Balancer(key_head_dim * num_heads,
channel_dim=-1,
min_positive=0.4,
max_positive=0.6,
min_abs=0.0,
max_abs=100.0,
prob=0.025)
# linear transformation for positional encoding.
self.linear_pos = ScaledLinear(pos_dim,
num_heads * pos_head_dim,
bias=False,
initial_scale=0.05)
# the following are for diagnosics only, see --print-diagnostics option
self.copy_pos_query = Identity()
self.copy_query = Identity()
def forward(
self,
x: Tensor,
pos_emb: Tensor,
chunk_size: int = -1,
key_padding_mask: Optional[Tensor] = None,
attn_mask: Optional[Tensor] = None,
) -> Tensor:
r"""
Args:
x: input of shape (seq_len, batch_size, embed_dim)
pos_emb: Positional embedding tensor, of shape (1, 2*seq_len - 2, pos_dim)
chunk_size
key_padding_mask: a bool tensor of shape (batch_size, seq_len). Positions that
are True in this mask will be ignored as sources in the attention weighting.
attn_mask: mask of shape (seq_len, seq_len) or (batch_size, seq_len, seq_len),
interpreted as ([batch_size,] tgt_seq_len, src_seq_len)
saying which positions are allowed to attend to which other positions.
Returns:
a tensor of attention weights, of shape (hum_heads, batch_size, seq_len, seq_len)
interpreted as (hum_heads, batch_size, tgt_seq_len, src_seq_len).
"""
x = self.in_proj(x)
query_head_dim = self.query_head_dim
pos_head_dim = self.pos_head_dim
num_heads = self.num_heads
seq_len, batch_size, _ = x.shape
query_dim = query_head_dim * num_heads
# self-attention
q = x[...,0:query_dim]
k = x[...,query_dim:2*query_dim]
# p is the position-encoding query
p = x[...,2*query_dim:]
assert p.shape[-1] == num_heads * pos_head_dim
q = self.copy_query(q) # for diagnostics only, does nothing.
k = self.whiten_keys(self.balance_keys(k)) # does nothing in the forward pass.
p = self.copy_pos_query(p) # for diagnostics only, does nothing.
q = q.reshape(seq_len, batch_size, num_heads, query_head_dim)
p = p.reshape(seq_len, batch_size, num_heads, pos_head_dim)
k = k.reshape(seq_len, batch_size, num_heads, query_head_dim)
# time1 refers to target, time2 refers to source.
q = q.permute(2, 1, 0, 3) # (head, batch, time1, query_head_dim)
p = p.permute(2, 1, 0, 3) # (head, batch, time1, pos_head_dim)
k = k.permute(2, 1, 3, 0) # (head, batch, d_k, time2)
attn_scores = torch.matmul(q, k)
if not self.training or random.random() >= float(self.pos_emb_skip_rate):
pos_emb = self.linear_pos(pos_emb)
seq_len2 = 2 * seq_len - 1
pos_emb = pos_emb.reshape(-1, seq_len2, num_heads, pos_head_dim).permute(2, 0, 3, 1)
# pos shape now: (head, {1 or batch_size}, pos_dim, seq_len2)
# (head, batch, time1, pos_dim) x (head, 1, pos_dim, seq_len2) -> (head, batch, time1, seq_len2)
# [where seq_len2 represents relative position.]
pos_scores = torch.matmul(p, pos_emb)
# the following .as_strided() expression converts the last axis of pos_scores from relative
# to absolute position. I don't know whether I might have got the time-offsets backwards or
# not, but let this code define which way round it is supposed to be.
pos_scores = pos_scores.as_strided((num_heads, batch_size, seq_len, seq_len),
(pos_scores.stride(0),
pos_scores.stride(1),
pos_scores.stride(2)-pos_scores.stride(3),
pos_scores.stride(3)),
storage_offset=pos_scores.stride(3) * (seq_len - 1))
attn_scores = attn_scores + pos_scores
if self.training and random.random() < 0.1:
# This is a harder way of limiting the attention scores to not be
# too large. It incurs a penalty if any of them has an absolute
# value greater than 50.0. this should be outside the normal range
# of the attention scores. We use this mechanism instead of, say,
# something added to the loss function involving the entropy,
# because once the entropy gets very small gradients through the
# softmax can become very small, and we'd get zero derivatives. The
# choices of 1.0e-04 as the scale on the penalty makes this
# mechanism vulnerable to the absolute scale of the loss function,
# but we view this as a failsafe to avoid "implausible" parameter
# values rather than a regularization method that should be active
# under normal circumstances.
attn_scores = penalize_abs_values_gt(attn_scores,
limit=25.0,
penalty=1.0e-04,
name=self.name)
assert attn_scores.shape == (num_heads, batch_size, seq_len, seq_len)
if attn_mask is not None:
assert attn_mask.dtype == torch.bool
# use -1000 to avoid nan's where attn_mask and key_padding_mask make
# all scores zero. It's important that this be large enough that exp(-1000)
# is exactly zero, for reasons related to const_attention_rate, it
# compares the final weights with zero.
attn_scores = attn_scores.masked_fill(attn_mask, -1000)
if key_padding_mask is not None:
assert key_padding_mask.shape == (batch_size, seq_len), key_padding_mask.shape
attn_scores = attn_scores.masked_fill(
key_padding_mask.unsqueeze(1),
-1000,
)
# We use our own version of softmax, defined in scaling.py, which should
# save a little of the memory used in backprop by, if we are in
# automatic mixed precision mode (amp / autocast), by only storing the
# half-precision output for backprop purposes.
attn_weights = softmax(attn_scores, dim=-1)
if random.random() < 0.001:
self._print_attn_entropy(attn_weights)
attn_weights = nn.functional.dropout(
attn_weights, p=self.dropout, training=self.training
)
return attn_weights
def _print_attn_entropy(
self,
attn_weights: Tensor):
# attn_weights: (num_heads, batch_size, seq_len, seq_len)
(num_heads, batch_size, seq_len, seq_len) = attn_weights.shape
with torch.no_grad():
with torch.cuda.amp.autocast(enabled=False):
attn_weights = attn_weights.to(torch.float32)
attn_weights_entropy = -((attn_weights + 1.0e-20).log() * attn_weights).sum(
dim=-1).mean(dim=(1,2))
logging.info(f"name={self.name}, attn_weights_entropy = {attn_weights_entropy}")
class SelfAttention(nn.Module):
"""
The simplest possible attention module. This one works with already-computed attention
weights, e.g. as computed by RelPositionMultiheadAttentionWeights.
Args:
embed_dim: the input and output embedding dimension
num_heads: the number of attention heads
value_head_dim: the value dimension per head
"""
def __init__(
self,
embed_dim: int,
num_heads: int,
value_head_dim: int,
) -> None:
super().__init__()
self.in_proj = nn.Linear(embed_dim,
num_heads * value_head_dim,
bias=True)
self.out_proj = ScaledLinear(num_heads * value_head_dim,
embed_dim, bias=True,
initial_scale=0.05)
self.whiten = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(7.5, ratio=3.0),
prob=(0.025, 0.25),
grad_scale=0.01)
def forward(
self,
x: Tensor,
attn_weights: Tensor,
) -> Tensor:
"""
Args:
x: input tensor, of shape (seq_len, batch_size, embed_dim)
attn_weights: a tensor of shape (num_heads, batch_size, seq_len, seq_len),
with seq_len being interpreted as (tgt_seq_len, src_seq_len). Expect
attn_weights.sum(dim=-1) == 1.
Returns:
a tensor with the same shape as x.
"""
(seq_len, batch_size, embed_dim) = x.shape
num_heads = attn_weights.shape[0]
assert attn_weights.shape == (num_heads, batch_size, seq_len, seq_len)
x = self.in_proj(x) # (seq_len, batch_size, num_heads * value_head_dim)
x = x.reshape(seq_len, batch_size, num_heads, -1).permute(2, 1, 0, 3)
# now x: (num_heads, batch_size, seq_len, value_head_dim)
value_head_dim = x.shape[-1]
# todo: see whether there is benefit in overriding matmul
x = torch.matmul(attn_weights, x)
# v: (num_heads, batch_size, seq_len, value_head_dim)
x = x.permute(2, 1, 0, 3).contiguous().view(
seq_len, batch_size, num_heads * value_head_dim)
# returned value is of shape (seq_len, batch_size, embed_dim), like the input.
x = self.out_proj(x)
x = self.whiten(x)
return x
class FeedforwardModule(nn.Module):
"""Feedforward module in Zipformer2 model.
"""
def __init__(self,
embed_dim: int,
feedforward_dim: int,
dropout: FloatLike):
super(FeedforwardModule, self).__init__()
self.in_proj = nn.Linear(embed_dim, feedforward_dim)
self.hidden_balancer = Balancer(feedforward_dim,
channel_dim=-1,
min_positive=0.3,
max_positive=1.0,
min_abs=0.75,
max_abs=5.0)
# shared_dim=0 means we share the dropout mask along the time axis
self.out_proj = ActivationDropoutAndLinear(feedforward_dim, embed_dim,
activation='SwooshL',
dropout_p=dropout,
dropout_shared_dim=0, bias=True,
initial_scale=0.1)
self.out_whiten = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(7.5),
prob=(0.025, 0.25),
grad_scale=0.01)
def forward(self,
x: Tensor):
x = self.in_proj(x)
x = self.hidden_balancer(x)
# out_proj contains SwooshL activation, then dropout, then linear.
x = self.out_proj(x)
x = self.out_whiten(x)
return x
class NonlinAttention(nn.Module):
"""This is like the ConvolutionModule, but refactored so that we use multiplication by attention weights (borrowed
from the attention module) in place of actual convolution. We also took out the second nonlinearity, the
one after the attention mechanism.
Args:
channels (int): The number of channels of conv layers.
"""
def __init__(
self,
channels: int,
hidden_channels: int,
) -> None:
super().__init__()
self.lr_scale = 0.95
self.hidden_channels = hidden_channels
self.in_proj = nn.Linear(channels, hidden_channels * 3, bias=True)
# balancer that goes before the sigmoid. Have quite a large min_abs value, at 2.0,
# because we noticed that well-trained instances of this module have abs-value before the sigmoid
# starting from about 3, and poorly-trained instances of the module have smaller abs values
# before the sigmoid.
self.balancer = Balancer(
hidden_channels, channel_dim=-1,
min_positive=ScheduledFloat((0.0, 0.25), (20000.0, 0.05)),
max_positive=ScheduledFloat((0.0, 0.75), (20000.0, 0.95)),
min_abs=0.5,
max_abs=5.0,
)
self.tanh = nn.Tanh()
self.identity1 = Identity() # for diagnostics.
self.identity2 = Identity() # for diagnostics.
self.identity3 = Identity() # for diagnostics.
self.out_proj = ScaledLinear(hidden_channels, channels,
bias=True,
initial_scale=0.05)
self.whiten1 = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(5.0),
prob=(0.025, 0.25),
grad_scale=0.01)
self.whiten2 = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(5.0, ratio=3.0),
prob=(0.025, 0.25),
grad_scale=0.01)
def forward(self,
x: Tensor,
attn_weights: Tensor,
) -> Tensor:
""".
Args:
x: a Tensor of shape (seq_len, batch_size, num_channels)
attn_weights: a Tensor of shape (num_heads, batch_size, seq_len, seq_len)
Returns:
a Tensor with the same shape as x
"""
num_channels = x.shape[-1]
x = self.in_proj(x)
(seq_len, batch_size, _) = x.shape
hidden_channels = self.hidden_channels
s, x, y = x.chunk(3, dim=-1)
# s will go through tanh.
s = self.balancer(s)
s = self.tanh(s)
s = s.unsqueeze(-1).reshape(seq_len, batch_size, hidden_channels)
x = self.whiten1(x)
x = x * s
x = self.identity1(x) # diagnostics only, it's the identity.
(seq_len, batch_size, embed_dim) = x.shape
num_heads = attn_weights.shape[0]
assert attn_weights.shape == (num_heads, batch_size, seq_len, seq_len)
x = x.reshape(seq_len, batch_size, num_heads, -1).permute(2, 1, 0, 3)
# now x: (num_heads, batch_size, seq_len, head_dim)
x = torch.matmul(attn_weights, x)
# now x: (num_heads, batch_size, seq_len, head_dim)
x = x.permute(2, 1, 0, 3).reshape(seq_len, batch_size, -1)
y = self.identity2(y)
x = x * y
x = self.identity3(x)
x = self.out_proj(x)
x = self.whiten2(x)
return x
class ConvolutionModule(nn.Module):
"""ConvolutionModule in Zipformer2 model.
Modified from https://github.com/espnet/espnet/blob/master/espnet/nets/pytorch_backend/zipformer/convolution.py
Args:
channels (int): The number of channels of conv layers.
kernel_size (int): Kernerl size of conv layers.
bias (bool): Whether to use bias in conv layers (default=True).
"""
def __init__(
self, channels: int, kernel_size: int, causal: bool,
) -> None:
"""Construct a ConvolutionModule object."""
super(ConvolutionModule, self).__init__()
# kernerl_size should be a odd number for 'SAME' padding
assert (kernel_size - 1) % 2 == 0
bottleneck_dim = channels
self.causal = causal
self.in_proj = nn.Linear(
channels, 2 * bottleneck_dim,
)
# the gradients on in_proj are a little noisy, likely to do with the
# sigmoid in glu.
self.in_proj.lr_scale = 0.9
# after in_proj we put x through a gated linear unit (nn.functional.glu).
# For most layers the normal rms value of channels of x seems to be in the range 1 to 4,
# but sometimes, for some reason, for layer 0 the rms ends up being very large,
# between 50 and 100 for different channels. This will cause very peaky and
# sparse derivatives for the sigmoid gating function, which will tend to make
# the loss function not learn effectively. (for most layers the average absolute values
# are in the range 0.5..9.0, and the average p(x>0), i.e. positive proportion,
# at the output of pointwise_conv1.output is around 0.35 to 0.45 for different
# layers, which likely breaks down as 0.5 for the "linear" half and
# 0.2 to 0.3 for the part that goes into the sigmoid. The idea is that if we
# constrain the rms values to a reasonable range via a constraint of max_abs=10.0,
# it will be in a better position to start learning something, i.e. to latch onto
# the correct range.
self.balancer1 = Balancer(
bottleneck_dim, channel_dim=-1,
min_positive=ScheduledFloat((0.0, 0.05), (8000.0, 0.025)),
max_positive=1.0,
min_abs=1.5,
max_abs=ScheduledFloat((0.0, 5.0), (8000.0, 10.0), default=1.0),
)
self.activation1 = Identity() # for diagnostics
self.sigmoid = nn.Sigmoid()
self.activation2 = Identity() # for diagnostics
assert kernel_size % 2 == 1
self.depthwise_conv = ChunkCausalDepthwiseConv1d(
channels=bottleneck_dim,
kernel_size=kernel_size) if causal else nn.Conv1d(
in_channels=bottleneck_dim,
out_channels=bottleneck_dim,
groups=bottleneck_dim,
kernel_size=kernel_size,
padding=kernel_size // 2)
self.balancer2 = Balancer(
bottleneck_dim, channel_dim=1,
min_positive=ScheduledFloat((0.0, 0.1), (8000.0, 0.05)),
max_positive=1.0,
min_abs=ScheduledFloat((0.0, 0.2), (20000.0, 0.5)),
max_abs=10.0,
)
self.whiten = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(7.5),
prob=(0.025, 0.25),
grad_scale=0.01)
self.out_proj = ActivationDropoutAndLinear(
bottleneck_dim, channels, activation='SwooshR',
dropout_p=0.0, initial_scale=0.05,
)
def forward(self,
x: Tensor,
src_key_padding_mask: Optional[Tensor] = None,
chunk_size: int = -1,
) -> Tensor:
"""Compute convolution module.
Args:
x: Input tensor (#time, batch, channels).
src_key_padding_mask: the mask for the src keys per batch (optional):
(batch, #time), contains True in masked positions.
Returns:
Tensor: Output tensor (#time, batch, channels).
"""
x = self.in_proj(x) # (time, batch, 2*channels)
x, s = x.chunk(2, dim=-1)
s = self.balancer1(s)
s = self.sigmoid(s)
x = self.activation1(x) # identity.
x = x * s
x = self.activation2(x) # identity
# (time, batch, channels)
# exchange the temporal dimension and the feature dimension
x = x.permute(1, 2, 0) # (#batch, channels, time).
if src_key_padding_mask is not None:
x = x.masked_fill(src_key_padding_mask.unsqueeze(1).expand_as(x), 0.0)
if chunk_size >= 0:
assert self.causal, "Must initialize model with causal=True if you use chunk_size"
x = self.depthwise_conv(x, chunk_size=chunk_size)
else:
x = self.depthwise_conv(x)
x = self.balancer2(x)
x = x.permute(2, 0, 1) # (time, batch, channels)
x = self.whiten(x) # (time, batch, channels)
x = self.out_proj(x) # (time, batch, channels)
return x
class ScalarMultiply(nn.Module):
def __init__(self, scale: float):
super().__init__()
self.scale = scale
def forward(self, x):
return x * self.scale
class ConvNeXt(nn.Module):
"""
Our interpretation of the ConvNeXt module as used in https://arxiv.org/pdf/2206.14747.pdf
"""
def __init__(self,
channels: int,
hidden_ratio: int = 3,
kernel_size: Tuple[int, int] = (7, 7),
layerdrop_rate: FloatLike = None):
super().__init__()
padding = ((kernel_size[0] - 1) // 2, (kernel_size[1] - 1) // 2)
hidden_channels = channels * hidden_ratio
if layerdrop_rate is None:
layerdrop_rate = ScheduledFloat((0.0, 0.2), (20000.0, 0.015))
self.layerdrop_rate = layerdrop_rate
self.depthwise_conv = nn.Conv2d(
in_channels=channels,
out_channels=channels,
groups=channels,
kernel_size=kernel_size,
padding=padding)
self.pointwise_conv1 = nn.Conv2d(
in_channels=channels,
out_channels=hidden_channels,
kernel_size=1)
self.hidden_balancer = Balancer(hidden_channels,
channel_dim=1,
min_positive=0.3,
max_positive=1.0,
min_abs=0.75,
max_abs=5.0)
self.activation = SwooshL()
self.pointwise_conv2 = ScaledConv2d(
in_channels=hidden_channels,
out_channels=channels,
kernel_size=1,
initial_scale=0.01)
self.out_balancer = Balancer(
channels, channel_dim=1,
min_positive=0.4, max_positive=0.6,
min_abs=1.0, max_abs=6.0,
)
self.out_whiten = Whiten(num_groups=1,
whitening_limit=5.0,
prob=(0.025, 0.25),
grad_scale=0.01)
def forward(self, x: Tensor) -> Tensor:
if torch.jit.is_scripting() or not self.training:
return self.forward_internal(x)
layerdrop_rate = float(self.layerdrop_rate)
if layerdrop_rate != 0.0:
batch_size = x.shape[0]
mask = torch.rand((batch_size, 1, 1, 1), dtype=x.dtype, device=x.device) > layerdrop_rate
else:
mask = None
# turns out this caching idea does not work with --world-size > 1
#return caching_eval(self.forward_internal, x, mask)
return self.forward_internal(x, mask)
def forward_internal(self,
x: Tensor,
layer_skip_mask: Optional[Tensor] = None) -> Tensor:
"""
x layout: (N, C, H, W), i.e. (batch_size, num_channels, num_frames, num_freqs)
The returned value has the same shape as x.
"""
bypass = x
x = self.depthwise_conv(x)
x = self.pointwise_conv1(x)
x = self.hidden_balancer(x)
x = self.activation(x)
x = self.pointwise_conv2(x)
if layer_skip_mask is not None:
x = x * layer_skip_mask
x = bypass + x
x = self.out_balancer(x)
x = x.transpose(1, 3) # (N, W, H, C); need channel dim to be last
x = self.out_whiten(x)
x = x.transpose(1, 3) # (N, C, H, W)
return x
class Conv2dSubsampling(nn.Module):
"""Convolutional 2D subsampling (to 1/2 length).
Convert an input of shape (N, T, idim) to an output
with shape (N, T', odim), where
T' = (T-3)//2 - 2 == (T-7)//2
It is based on
https://github.com/espnet/espnet/blob/master/espnet/nets/pytorch_backend/transformer/subsampling.py # noqa
"""
def __init__(
self,
in_channels: int,
out_channels: int,
layer1_channels: int = 8,
layer2_channels: int = 32,
layer3_channels: int = 64,
dropout: FloatLike = 0.1,
) -> None:
"""
Args:
in_channels:
Number of channels in. The input shape is (N, T, in_channels).
Caution: It requires: T >=7, in_channels >=7
out_channels
Output dim. The output shape is (N, (T-3)//2, out_channels)
layer1_channels:
Number of channels in layer1
layer1_channels:
Number of channels in layer2
bottleneck:
bottleneck dimension for 1d squeeze-excite
"""
assert in_channels >= 7
super().__init__()
# The ScaleGrad module is there to prevent the gradients
# w.r.t. the weight or bias of the first Conv2d module in self.conv from
# exceeding the range of fp16 when using automatic mixed precision (amp)
# training. (The second one is necessary to stop its bias from getting
# a too-large gradient).
self.conv = nn.Sequential(
nn.Conv2d(
in_channels=1,
out_channels=layer1_channels,
kernel_size=3,
padding=(0, 1), # (time, freq)
),
ScaleGrad(0.2),
Balancer(layer1_channels,
channel_dim=1,
max_abs=1.0),
SwooshR(),
nn.Conv2d(
in_channels=layer1_channels,
out_channels=layer2_channels,
kernel_size=3,
stride=2,
padding=0,
),
Balancer(layer2_channels,
channel_dim=1,
max_abs=4.0),
SwooshR(),
nn.Conv2d(
in_channels=layer2_channels,
out_channels=layer3_channels,
kernel_size=3,
stride=(1, 2), # (time, freq)
),
Balancer(layer3_channels,
channel_dim=1,
max_abs=4.0),
SwooshR(),
)
cur_width = (in_channels - 1) // 2
# just one convnext layer
self.convnext = ConvNeXt(layer3_channels, kernel_size=(7, 7))
out_width = (((in_channels - 1) // 2) - 1) // 2
self.out = nn.Linear(out_width * layer3_channels, out_channels)
# use a larger than normal grad_scale on this whitening module; there is
# only one such module, so there is not a concern about adding together
# many copies of this extra gradient term.
self.out_whiten = Whiten(num_groups=1,
whitening_limit=_whitening_schedule(4.0),
prob=(0.025, 0.25),
grad_scale=0.02)
# max_log_eps=0.0 is to prevent both eps and the output of self.out from
# getting large, there is an unnecessary degree of freedom.
self.out_norm = BiasNorm(out_channels)
self.dropout = Dropout3(dropout, shared_dim=1)
def forward(self, x: torch.Tensor) -> torch.Tensor:
"""Subsample x.
Args:
x:
Its shape is (N, T, idim).
Returns:
Return a tensor of shape (N, ((T-1)//2 - 1)//2, odim)
"""
# On entry, x is (N, T, idim)
x = x.unsqueeze(1) # (N, T, idim) -> (N, 1, T, idim) i.e., (N, C, H, W)
# scaling x by 0.1 allows us to use a larger grad-scale in fp16 "amp" (automatic mixed precision)
# training, since the weights in the first convolution are otherwise the limiting factor for getting infinite
# gradients.
x = self.conv(x)
x = self.convnext(x)
# Now x is of shape (N, odim, ((T-3)//2 - 1)//2, ((idim-1)//2 - 1)//2)
b, c, t, f = x.size()
x = x.transpose(1, 2).reshape(b, t, c * f)
# now x: (N, ((T-1)//2 - 1))//2, out_width * layer3_channels))
x = self.out(x)
# Now x is of shape (N, ((T-1)//2 - 1))//2, odim)
x = self.out_whiten(x)
x = self.out_norm(x)
x = self.dropout(x)
return x
def _test_zipformer_main(causal: bool = False):
feature_dim = 50
batch_size = 5
seq_len = 20
feature_dim = 50
# Just make sure the forward pass runs.
c = Zipformer2(
num_features=feature_dim, encoder_dim=(64,96), encoder_unmasked_dim=(48,64), num_heads=(4,4),
causal=causal,
chunk_size=(4,) if causal else (-1,),
left_context_frames=(64,)
)
batch_size = 5
seq_len = 20
# Just make sure the forward pass runs.
f = c(
torch.randn(batch_size, seq_len, feature_dim),
torch.full((batch_size,), seq_len, dtype=torch.int64),
)
f[0].sum().backward()
c.eval()
f = c(
torch.randn(batch_size, seq_len, feature_dim),
torch.full((batch_size,), seq_len, dtype=torch.int64),
)
f # to remove flake8 warnings
if __name__ == "__main__":
logging.getLogger().setLevel(logging.INFO)
torch.set_num_threads(1)
torch.set_num_interop_threads(1)
_test_zipformer_main(False)
_test_zipformer_main(True)
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