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| # Copyright (c) 2019 Shigeki Karita | |
| # 2020 Mobvoi Inc (Binbin Zhang) | |
| # 2022 Xingchen Song (sxc19@mails.tsinghua.edu.cn) | |
| # 2022 58.com(Wuba) Inc AI Lab. | |
| # | |
| # 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. | |
| """Multi-Head Attention layer definition.""" | |
| import math | |
| from typing import Tuple, Optional | |
| import torch | |
| from torch import nn | |
| import torch.nn.functional as F | |
| from wenet.transformer.attention import MultiHeadedAttention | |
| class GroupedRelPositionMultiHeadedAttention(MultiHeadedAttention): | |
| """Multi-Head Attention layer with relative position encoding. | |
| Paper: | |
| https://arxiv.org/abs/1901.02860 | |
| https://arxiv.org/abs/2109.01163 | |
| Args: | |
| n_head (int): The number of heads. | |
| n_feat (int): The number of features. | |
| dropout_rate (float): Dropout rate. | |
| """ | |
| def __init__(self, n_head, n_feat, dropout_rate, group_size=3): | |
| """Construct an RelPositionMultiHeadedAttention object.""" | |
| super().__init__(n_head, n_feat, dropout_rate) | |
| # linear transformation for positional encoding | |
| self.linear_pos = nn.Linear(n_feat, n_feat, bias=False) | |
| self.group_size = group_size | |
| self.d_k = n_feat // n_head # for GroupedAttention | |
| self.n_feat = n_feat | |
| # these two learnable bias are used in matrix c and matrix d | |
| # as described in https://arxiv.org/abs/1901.02860 Section 3.3 | |
| self.pos_bias_u = nn.Parameter( | |
| torch.Tensor(self.h, self.d_k * self.group_size)) | |
| self.pos_bias_v = nn.Parameter( | |
| torch.Tensor(self.h, self.d_k * self.group_size)) | |
| torch.nn.init.xavier_uniform_(self.pos_bias_u) | |
| torch.nn.init.xavier_uniform_(self.pos_bias_v) | |
| def rel_shift(self, x, zero_triu: bool = False): | |
| """Compute relative positinal encoding. | |
| Args: | |
| x (torch.Tensor): Input tensor (batch, time, size). | |
| zero_triu (bool): If true, return the lower triangular part of | |
| the matrix. | |
| Returns: | |
| torch.Tensor: Output tensor. | |
| """ | |
| zero_pad = torch.zeros((x.size()[0], x.size()[1], x.size()[2], 1), | |
| device=x.device, | |
| dtype=x.dtype) | |
| x_padded = torch.cat([zero_pad, x], dim=-1) | |
| x_padded = x_padded.view(x.size()[0], | |
| x.size()[1], | |
| x.size(3) + 1, x.size(2)) | |
| x = x_padded[:, :, 1:].view_as(x) | |
| if zero_triu: | |
| ones = torch.ones((x.size(2), x.size(3))) | |
| x = x * torch.tril(ones, x.size(3) - x.size(2))[None, None, :, :] | |
| return x | |
| def pad4group(self, Q, K, V, P, mask, group_size: int = 3): | |
| """ | |
| q: (#batch, time1, size) -> (#batch, head, time1, size/head) | |
| k,v: (#batch, time2, size) -> (#batch, head, time2, size/head) | |
| p: (#batch, time2, size) | |
| """ | |
| # Compute Overflows | |
| overflow_Q = Q.size(2) % group_size | |
| overflow_KV = K.size(2) % group_size | |
| # if-else for ONNX export | |
| # 0 // 0.00000000000000001 = 0 | |
| # 1 // 1.00000000000000001 = 1 | |
| padding_Q = (group_size - overflow_Q) * int( | |
| overflow_Q // (overflow_Q + 0.00000000000000001)) | |
| padding_KV = (group_size - overflow_KV) * int( | |
| overflow_KV // (overflow_KV + 0.00000000000000001)) | |
| batch_size, _, seq_len_KV, _ = K.size() | |
| # Input Padding (B, T, D) -> (B, T + P, D) | |
| Q = F.pad(Q, (0, 0, 0, padding_Q), value=0.0) | |
| K = F.pad(K, (0, 0, 0, padding_KV), value=0.0) | |
| V = F.pad(V, (0, 0, 0, padding_KV), value=0.0) | |
| if mask is not None and mask.size(2) > 0: # time2 > 0: | |
| mask = mask[:, ::group_size, ::group_size] | |
| Q = Q.transpose(1, 2).contiguous().view( | |
| batch_size, -1, self.h, self.d_k * group_size).transpose(1, 2) | |
| K = K.transpose(1, 2).contiguous().view( | |
| batch_size, -1, self.h, self.d_k * group_size).transpose(1, 2) | |
| V = V.transpose(1, 2).contiguous().view( | |
| batch_size, -1, self.h, self.d_k * group_size).transpose(1, 2) | |
| # process pos_emb | |
| P_batch_size = P.size(0) | |
| overflow_P = P.size(1) % group_size | |
| padding_P = group_size - overflow_P if overflow_P else 0 | |
| P = F.pad(P, (0, 0, 0, padding_P), value=0.0) | |
| P = P.view(P_batch_size, -1, self.h, | |
| self.d_k * group_size).transpose(1, 2) | |
| return Q, K, V, P, mask, padding_Q | |
| def forward_attention(self, | |
| value: torch.Tensor, | |
| scores: torch.Tensor, | |
| mask: torch.Tensor = torch.ones((0, 0, 0), | |
| dtype=torch.bool), | |
| padding_q: Optional[int] = None) -> torch.Tensor: | |
| """Compute attention context vector. | |
| Args: | |
| value (torch.Tensor): Transformed value, size | |
| (#batch, n_head, time2, d_k). | |
| scores (torch.Tensor): Attention score, size | |
| (#batch, n_head, time1, time2). | |
| mask (torch.Tensor): Mask, size (#batch, 1, time2) or | |
| (#batch, time1, time2), (0, 0, 0) means fake mask. | |
| padding_q : for GroupedAttention in efficent conformer | |
| Returns: | |
| torch.Tensor: Transformed value (#batch, time1, d_model) | |
| weighted by the attention score (#batch, time1, time2). | |
| """ | |
| n_batch = value.size(0) | |
| # NOTE(xcsong): When will `if mask.size(2) > 0` be True? | |
| # 1. onnx(16/4) [WHY? Because we feed real cache & real mask for the | |
| # 1st chunk to ease the onnx export.] | |
| # 2. pytorch training | |
| if mask.size(2) > 0: # time2 > 0 | |
| mask = mask.unsqueeze(1).eq(0) # (batch, 1, *, time2) | |
| # For last chunk, time2 might be larger than scores.size(-1) | |
| mask = mask[:, :, :, :scores.size(-1)] # (batch, 1, *, time2) | |
| scores = scores.masked_fill(mask, -float('inf')) | |
| attn = torch.softmax(scores, dim=-1).masked_fill( | |
| mask, 0.0) # (batch, head, time1, time2) | |
| # NOTE(xcsong): When will `if mask.size(2) > 0` be False? | |
| # 1. onnx(16/-1, -1/-1, 16/0) | |
| # 2. jit (16/-1, -1/-1, 16/0, 16/4) | |
| else: | |
| attn = torch.softmax(scores, dim=-1) # (batch, head, time1, time2) | |
| p_attn = self.dropout(attn) | |
| x = torch.matmul(p_attn, value) # (batch, head, time1, d_k) | |
| # n_feat!=h*d_k may be happened in GroupAttention | |
| x = (x.transpose(1, 2).contiguous().view(n_batch, -1, self.n_feat) | |
| ) # (batch, time1, d_model) | |
| if padding_q is not None: | |
| # for GroupedAttention in efficent conformer | |
| x = x[:, :x.size(1) - padding_q] | |
| return self.linear_out(x) # (batch, time1, d_model) | |
| def forward( | |
| self, | |
| query: torch.Tensor, | |
| key: torch.Tensor, | |
| value: torch.Tensor, | |
| mask: torch.Tensor = torch.ones((0, 0, 0), dtype=torch.bool), | |
| pos_emb: torch.Tensor = torch.empty(0), | |
| cache: torch.Tensor = torch.zeros((0, 0, 0, 0)), | |
| ) -> Tuple[torch.Tensor, torch.Tensor]: | |
| """Compute 'Scaled Dot Product Attention' with rel. positional encoding. | |
| Args: | |
| query (torch.Tensor): Query tensor (#batch, time1, size). | |
| key (torch.Tensor): Key tensor (#batch, time2, size). | |
| value (torch.Tensor): Value tensor (#batch, time2, size). | |
| mask (torch.Tensor): Mask tensor (#batch, 1, time2) or | |
| (#batch, time1, time2). | |
| pos_emb (torch.Tensor): Positional embedding tensor | |
| (#batch, time2, size). | |
| cache (torch.Tensor): Cache tensor (1, head, cache_t, d_k * 2), | |
| where `cache_t == chunk_size * num_decoding_left_chunks` | |
| and `head * d_k == size` | |
| Returns: | |
| torch.Tensor: Output tensor (#batch, time1, d_model). | |
| torch.Tensor: Cache tensor (1, head, cache_t + time1, d_k * 2) | |
| where `cache_t == chunk_size * num_decoding_left_chunks` | |
| and `head * d_k == size` | |
| """ | |
| q = self.linear_q(query) | |
| k = self.linear_k(key) # (#batch, time2, size) | |
| v = self.linear_v(value) | |
| p = self.linear_pos(pos_emb) # (#batch, time2, size) | |
| batch_size, seq_len_KV, _ = k.size() # seq_len_KV = time2 | |
| # (#batch, time2, size) -> (#batch, head, time2, size/head) | |
| q = q.view(batch_size, -1, self.h, self.d_k).transpose(1, 2) | |
| k = k.view(batch_size, -1, self.h, self.d_k).transpose(1, 2) | |
| v = v.view(batch_size, -1, self.h, self.d_k).transpose(1, 2) | |
| if cache.size(0) > 0: | |
| # use attention cache | |
| key_cache, value_cache = torch.split(cache, | |
| cache.size(-1) // 2, | |
| dim=-1) | |
| k = torch.cat([key_cache, k], dim=2) | |
| v = torch.cat([value_cache, v], dim=2) | |
| new_cache = torch.cat((k, v), dim=-1) | |
| # May be k and p does not match. eg. time2=18+18/2=27 > mask=36/2=18 | |
| if mask is not None and mask.size(2) > 0: | |
| time2 = mask.size(2) | |
| k = k[:, :, -time2:, :] | |
| v = v[:, :, -time2:, :] | |
| # q k v p: (batch, head, time1, d_k) | |
| q, k, v, p, mask, padding_q = self.pad4group(q, k, v, p, mask, | |
| self.group_size) | |
| # q_with_bias_u & q_with_bias_v = (batch, head, time1, d_k) | |
| q = q.transpose(1, 2) # (batch, time1, head, d_k) | |
| q_with_bias_u = (q + self.pos_bias_u).transpose(1, 2) | |
| q_with_bias_v = (q + self.pos_bias_v).transpose(1, 2) | |
| # compute attention score | |
| # first compute matrix a and matrix c | |
| # as described in https://arxiv.org/abs/1901.02860 Section 3.3 | |
| # (batch, head, time1, time2) | |
| matrix_ac = torch.matmul(q_with_bias_u, k.transpose(-2, -1)) | |
| # compute matrix b and matrix d | |
| # (batch, head, time1, time2) | |
| matrix_bd = torch.matmul(q_with_bias_v, p.transpose(-2, -1)) | |
| # Remove rel_shift since it is useless in speech recognition, | |
| # and it requires special attention for streaming. | |
| # matrix_bd = self.rel_shift(matrix_bd) | |
| scores = (matrix_ac + matrix_bd) / math.sqrt( | |
| self.d_k * self.group_size) # (batch, head, time1, time2) | |
| return self.forward_attention(v, scores, mask, padding_q), new_cache | |