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modeling_switch_transformers.py
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modeling_switch_transformers.py
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# coding=utf-8
# Copyright 2022 SwitchTransformers Authors and HuggingFace Inc. 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.
""" PyTorch SwitchTransformers model."""
import copy
import math
import warnings
from typing import Optional, Tuple, Union
import torch
import torch.nn as nn
from torch.nn import CrossEntropyLoss
from torch.utils.checkpoint import checkpoint
from ...activations import ACT2FN
from ...modeling_outputs import (
MoEModelOutput,
MoEModelOutputWithPastAndCrossAttentions,
Seq2SeqMoEModelOutput,
Seq2SeqMoEOutput,
)
from ...modeling_utils import PreTrainedModel
from ...pytorch_utils import ALL_LAYERNORM_LAYERS, find_pruneable_heads_and_indices, prune_linear_layer
from ...utils import (
DUMMY_INPUTS,
DUMMY_MASK,
add_start_docstrings,
add_start_docstrings_to_model_forward,
is_torch_fx_proxy,
logging,
replace_return_docstrings,
)
from .configuration_switch_transformers import SwitchTransformersConfig
logger = logging.get_logger(__name__)
_CONFIG_FOR_DOC = "SwitchTransformersConfig"
_CHECKPOINT_FOR_DOC = "google/switch-base-8"
####################################################
# This dict contains ids and associated url
# for the pretrained weights provided with the models
####################################################
SWITCH_TRANSFORMERS_PRETRAINED_MODEL_ARCHIVE_LIST = [
"google/switch-base-8",
"google/switch-base-16",
"google/switch-base-32",
"google/switch-base-64",
"google/switch-base-128",
"google/switch-base-256",
"google/switch-large-128",
"google/switch-xxl-128",
"google/switch-c-2048",
# See all SwitchTransformers models at https://huggingface.co/models?filter=switch_transformers
]
def router_z_loss_func(router_logits: torch.Tensor) -> float:
r"""
Compute the router z-loss implemented in PyTorch.
The router z-loss was introduced in [Designing Effective Sparse Expert Models](https://arxiv.org/abs/2202.08906).
It encourages router logits to remain small in an effort to improve stability.
Args:
router_logits (`float`):
Input logits of shape [batch_size, sequence_length, num_experts]
Returns:
Scalar router z-loss.
"""
num_groups, tokens_per_group, _ = router_logits.shape
log_z = torch.logsumexp(router_logits, dim=-1)
z_loss = log_z**2
return torch.sum(z_loss) / (num_groups * tokens_per_group)
def load_balancing_loss_func(router_probs: torch.Tensor, expert_indices: torch.Tensor) -> float:
r"""
Computes auxiliary load balancing loss as in Switch Transformer - implemented in Pytorch.
See Switch Transformer (https://arxiv.org/abs/2101.03961) for more details. This function implements the loss
function presented in equations (4) - (6) of the paper. It aims at penalizing cases where the routing between
experts is too unbalanced.
Args:
router_probs (`torch.Tensor`):
Probability assigned to each expert per token. Shape: [batch_size, seqeunce_length, num_experts].
expert_indices (`torch.Tensor`):
Indices tensor of shape [batch_size, seqeunce_length] identifying the selected expert for a given token.
Returns:
The auxiliary loss.
"""
num_experts = router_probs.shape[-1]
# cast the expert indices to int64, otherwise one-hot encoding will fail
if expert_indices.dtype != torch.int64:
expert_indices = expert_indices.to(torch.int64)
if len(expert_indices.shape) == 2:
expert_indices = expert_indices.unsqueeze(2)
expert_mask = torch.nn.functional.one_hot(expert_indices, num_experts)
# For a given token, determine if it was routed to a given expert.
expert_mask = torch.max(expert_mask, axis=-2).values
# cast to float32 otherwise mean will fail
expert_mask = expert_mask.to(torch.float32)
tokens_per_group_and_expert = torch.mean(expert_mask, axis=-2)
router_prob_per_group_and_expert = torch.mean(router_probs, axis=-2)
return torch.mean(tokens_per_group_and_expert * router_prob_per_group_and_expert) * (num_experts**2)
class SwitchTransformersTop1Router(nn.Module):
"""
Router using tokens choose top-1 experts assignment.
This router uses the same mechanism as in Switch Transformer (https://arxiv.org/abs/2101.03961) and V-MoE
(https://arxiv.org/abs/2106.05974): tokens choose their top experts. Items are sorted by router_probs and then
routed to their choice of expert until the expert's expert_capacity is reached. **There is no guarantee that each
token is processed by an expert**, or that each expert receives at least one token.
"""
def __init__(self, config: SwitchTransformersConfig):
super().__init__()
self.num_experts = config.num_experts
self.expert_capacity = config.expert_capacity
self.classifier = nn.Linear(config.hidden_size, self.num_experts, bias=config.router_bias)
self.jitter_noise = config.router_jitter_noise
self.ignore_padding_tokens = config.router_ignore_padding_tokens
self.dtype = getattr(torch, config.router_dtype)
def _compute_router_probabilities(self, hidden_states: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
r"""
Computes router probabilities from input hidden states.
Args:
hidden_states (`torch.Tensor`):
(batch_size, sequence_length, hidden_dim) from which router probabilities are computed.
Returns:
router_probabilities (`torch.Tensor`):
Tensor of shape (batch_size, sequence_length, num_experts) corresponding to the probabilities for each
token and expert. Used for routing tokens to experts.
router_logits (`torch.Tensor`):
Logits tensor of shape (batch_size, sequence_length, num_experts) corresponding to raw router logits.
This is used later for computing router z-loss.
"""
# float32 is used to ensure stability. See the discussion of "selective precision" in
# https://arxiv.org/abs/2101.03961.
# We also store the previous dtype to cast back the output to the previous dtype
self.input_dtype = hidden_states.dtype
hidden_states = hidden_states.to(self.dtype)
if self.jitter_noise > 0:
# Get the lower and upper bound of the uniform distribution
# Adapted from: https://stackoverflow.com/questions/44328530/how-to-get-a-uniform-distribution-in-a-range-r1-r2-in-pytorch
distrib_lower_bound = 1.0 - self.jitter_noise
distrib_upper_bound = 1.0 + self.jitter_noise
uniform_distrib = torch.rand(hidden_states.shape, device=hidden_states.device, dtype=self.dtype)
uniform_distrib = uniform_distrib * (distrib_lower_bound - distrib_upper_bound)
uniform_distrib = uniform_distrib + distrib_upper_bound
# Multiply the token inputs by the uniform distribution - adding some noise
hidden_states *= uniform_distrib
# Shape: [num_groups, tokens_per_group, num_experts]
self._cast_classifier()
router_logits = self.classifier(hidden_states)
# Apply Softmax and cast back to the original `dtype`
router_probabilities = nn.functional.softmax(router_logits, dim=-1, dtype=self.dtype).to(self.input_dtype)
return router_probabilities, router_logits
def _cast_classifier(self):
r"""
`bitsandbytes` `Linear8bitLt` layers does not support manual casting Therefore we need to check if they are an
instance of the `Linear8bitLt` class by checking special attributes.
"""
if not (hasattr(self.classifier, "SCB") or hasattr(self.classifier, "CB")):
self.classifier = self.classifier.to(self.dtype)
def forward(self, hidden_states: torch.Tensor) -> Tuple:
r"""
Generic forward function for every Router class. Each Router expects to have the same input hidden states
(`hidden_states`) corresponding to the hidden states for each token, the `expert_capacity` corresponding to the
number of tokens the Router will send to each expert, some Routers can send up to few tokens to each expert.
Each Router works as the following: it expects the hidden states for each token, gets the `router_probs` and
`router_logits` from the `router_weights`. This will assign for each token, the raw probability to be assigned
to an expert. Then each Router class will have to define its own `_compute_routing_instructions`.
Args:
hidden_states (`torch.Tensor`) :
[num_groups, tokens_per_group, hidden_dim] inputs to send to experts.
Returns:
Tuple[`torch.Tensor`, `torch.Tensor`, `torch.Tensor`] Tuple containing the expert index, the router probs
and the router logits. The router probabilities and logits are required to compute the loss.
"""
router_probs, router_logits = self._compute_router_probabilities(hidden_states)
expert_index = torch.argmax(router_probs, dim=-1)
expert_index = torch.nn.functional.one_hot(expert_index, num_classes=self.num_experts)
# Mask tokens outside expert capacity. Sum over each sequence
token_priority = torch.cumsum(expert_index, dim=-2)
# mask if the token routed to to the expert will overflow
expert_capacity_mask = token_priority <= self.expert_capacity
expert_index = expert_index * expert_capacity_mask
router_probs = torch.max(router_probs, dim=-1).values.unsqueeze(-1)
return expert_index, router_probs, router_logits
# Copied from transformers.models.t5.modeling_t5.T5LayerNorm with T5->SwitchTransformers
class SwitchTransformersLayerNorm(nn.Module):
def __init__(self, hidden_size, eps=1e-6):
"""
Construct a layernorm module in the SwitchTransformers style. No bias and no subtraction of mean.
"""
super().__init__()
self.weight = nn.Parameter(torch.ones(hidden_size))
self.variance_epsilon = eps
def forward(self, hidden_states):
# SwitchTransformers uses a layer_norm which only scales and doesn't shift, which is also known as Root Mean
# Square Layer Normalization https://arxiv.org/abs/1910.07467 thus varience is calculated
# w/o mean and there is no bias. Additionally we want to make sure that the accumulation for
# half-precision inputs is done in fp32
variance = hidden_states.to(torch.float32).pow(2).mean(-1, keepdim=True)
hidden_states = hidden_states * torch.rsqrt(variance + self.variance_epsilon)
# convert into half-precision if necessary
if self.weight.dtype in [torch.float16, torch.bfloat16]:
hidden_states = hidden_states.to(self.weight.dtype)
return self.weight * hidden_states
ALL_LAYERNORM_LAYERS.append(SwitchTransformersLayerNorm)
# Copied from transformers.models.t5.modeling_t5.T5DenseActDense with T5->SwitchTransformers
class SwitchTransformersDenseActDense(nn.Module):
def __init__(self, config: SwitchTransformersConfig):
super().__init__()
self.wi = nn.Linear(config.d_model, config.d_ff, bias=False)
self.wo = nn.Linear(config.d_ff, config.d_model, bias=False)
self.dropout = nn.Dropout(config.dropout_rate)
self.act = ACT2FN[config.dense_act_fn]
def forward(self, hidden_states):
hidden_states = self.wi(hidden_states)
hidden_states = self.act(hidden_states)
hidden_states = self.dropout(hidden_states)
if (
isinstance(self.wo.weight, torch.Tensor)
and hidden_states.dtype != self.wo.weight.dtype
and self.wo.weight.dtype != torch.int8
):
hidden_states = hidden_states.to(self.wo.weight.dtype)
hidden_states = self.wo(hidden_states)
return hidden_states
class SwitchTransformersSparseMLP(nn.Module):
r"""
Implementation of the Switch Transformers Sparse MLP module.
"""
def __init__(self, config: SwitchTransformersConfig, expert_class: nn.Module = SwitchTransformersDenseActDense):
super().__init__()
# Step 1: Get the correct router according to its class
self.router = SwitchTransformersTop1Router(config)
# Step 2: Get the experts
self.experts = nn.ModuleDict()
for idx in range(config.num_experts):
self.experts[f"expert_{idx}"] = expert_class(config)
def forward(self, hidden_states):
r"""
Hold on, this will be slightly tricky to understand In the correct order, a MoE layer does the following:
1- Gets the `router_mask` from the router. The shape of the mask is `(batch_size, sequence_length, num_expert)`
and corresponds to the argmax of the `router_probs`. The probabilities are needed in the computation of the
hidden states : they are broadcasted to the hidden states values (can be interpreted as a scaling factor).
2- Dispatch the tokens to its associated experts. We do a classic for loop over the experts and assign for each
expert the corresponding hidden states.
"""
# Step 1: Get the router_mask from the router as wel as the probabilities
router_mask, router_probs, router_logits = self.router(hidden_states)
expert_index = torch.argmax(router_mask, dim=-1)
# The routers introduced might not always map all the tokens, to a router, which means that some hidden states
# can be unchanged from one layer to another. That is why the hidden states are cloned before updating only the seleced ones.
next_states = hidden_states.clone()
for idx, expert in enumerate(self.experts.values()):
token_indices = router_mask[:, :, idx].bool()
next_states[token_indices] = expert(hidden_states[token_indices])
hidden_states = router_probs * next_states
return hidden_states, (router_logits, expert_index)
class SwitchTransformersLayerFF(nn.Module):
r"""
Switch Transformers Feed Forward layer module. This is a wrapper around the Mixture of Experts module.
Parameters:
config : ([`SwitchTransformersConfig`]): Model configuration class with all the parameters of the model.
Initializing with a config file does not load the weights associated with the model, only the
configuration. Check out the [`~PreTrainedModel.from_pretrained`] method to load the model weights.
is_sparse (`bool`):
Whether the MLP layer is a `Sparse` layer (contains a Mixture of Experts) or not
"""
def __init__(self, config: SwitchTransformersConfig, is_sparse=False):
super().__init__()
self.is_sparse = is_sparse
# Check if it is a sparse layer, if not then it is a dense layer
if not self.is_sparse:
self.mlp = SwitchTransformersDenseActDense(config)
else:
self.mlp = SwitchTransformersSparseMLP(config)
self.layer_norm = SwitchTransformersLayerNorm(config.d_model, eps=config.layer_norm_epsilon)
self.dropout = nn.Dropout(config.dropout_rate)
def forward(self, hidden_states, output_router_logits):
forwarded_states = self.layer_norm(hidden_states)
forwarded_states = self.mlp(forwarded_states)
if isinstance(forwarded_states, tuple):
forwarded_states, router_tuple = forwarded_states
else:
router_tuple = None
output = hidden_states + self.dropout(forwarded_states)
if output_router_logits and router_tuple is not None:
output = (output, router_tuple)
return output
# Copied from transformers.models.t5.modeling_t5.T5Attention with T5->SwitchTransformers
class SwitchTransformersAttention(nn.Module):
def __init__(self, config: SwitchTransformersConfig, has_relative_attention_bias=False):
super().__init__()
self.is_decoder = config.is_decoder
self.has_relative_attention_bias = has_relative_attention_bias
self.relative_attention_num_buckets = config.relative_attention_num_buckets
self.relative_attention_max_distance = config.relative_attention_max_distance
self.d_model = config.d_model
self.key_value_proj_dim = config.d_kv
self.n_heads = config.num_heads
self.dropout = config.dropout_rate
self.inner_dim = self.n_heads * self.key_value_proj_dim
# Mesh TensorFlow initialization to avoid scaling before softmax
self.q = nn.Linear(self.d_model, self.inner_dim, bias=False)
self.k = nn.Linear(self.d_model, self.inner_dim, bias=False)
self.v = nn.Linear(self.d_model, self.inner_dim, bias=False)
self.o = nn.Linear(self.inner_dim, self.d_model, bias=False)
if self.has_relative_attention_bias:
self.relative_attention_bias = nn.Embedding(self.relative_attention_num_buckets, self.n_heads)
self.pruned_heads = set()
self.gradient_checkpointing = False
def prune_heads(self, heads):
if len(heads) == 0:
return
heads, index = find_pruneable_heads_and_indices(
heads, self.n_heads, self.key_value_proj_dim, self.pruned_heads
)
# Prune linear layers
self.q = prune_linear_layer(self.q, index)
self.k = prune_linear_layer(self.k, index)
self.v = prune_linear_layer(self.v, index)
self.o = prune_linear_layer(self.o, index, dim=1)
# Update hyper params
self.n_heads = self.n_heads - len(heads)
self.inner_dim = self.key_value_proj_dim * self.n_heads
self.pruned_heads = self.pruned_heads.union(heads)
@staticmethod
def _relative_position_bucket(relative_position, bidirectional=True, num_buckets=32, max_distance=128):
"""
Adapted from Mesh Tensorflow:
https://github.com/tensorflow/mesh/blob/0cb87fe07da627bf0b7e60475d59f95ed6b5be3d/mesh_tensorflow/transformer/transformer_layers.py#L593
Translate relative position to a bucket number for relative attention. The relative position is defined as
memory_position - query_position, i.e. the distance in tokens from the attending position to the attended-to
position. If bidirectional=False, then positive relative positions are invalid. We use smaller buckets for
small absolute relative_position and larger buckets for larger absolute relative_positions. All relative
positions >=max_distance map to the same bucket. All relative positions <=-max_distance map to the same bucket.
This should allow for more graceful generalization to longer sequences than the model has been trained on
Args:
relative_position: an int32 Tensor
bidirectional: a boolean - whether the attention is bidirectional
num_buckets: an integer
max_distance: an integer
Returns:
a Tensor with the same shape as relative_position, containing int32 values in the range [0, num_buckets)
"""
relative_buckets = 0
if bidirectional:
num_buckets //= 2
relative_buckets += (relative_position > 0).to(torch.long) * num_buckets
relative_position = torch.abs(relative_position)
else:
relative_position = -torch.min(relative_position, torch.zeros_like(relative_position))
# now relative_position is in the range [0, inf)
# half of the buckets are for exact increments in positions
max_exact = num_buckets // 2
is_small = relative_position < max_exact
# The other half of the buckets are for logarithmically bigger bins in positions up to max_distance
relative_position_if_large = max_exact + (
torch.log(relative_position.float() / max_exact)
/ math.log(max_distance / max_exact)
* (num_buckets - max_exact)
).to(torch.long)
relative_position_if_large = torch.min(
relative_position_if_large, torch.full_like(relative_position_if_large, num_buckets - 1)
)
relative_buckets += torch.where(is_small, relative_position, relative_position_if_large)
return relative_buckets
def compute_bias(self, query_length, key_length, device=None):
"""Compute binned relative position bias"""
if device is None:
device = self.relative_attention_bias.weight.device
context_position = torch.arange(query_length, dtype=torch.long, device=device)[:, None]
memory_position = torch.arange(key_length, dtype=torch.long, device=device)[None, :]
relative_position = memory_position - context_position # shape (query_length, key_length)
relative_position_bucket = self._relative_position_bucket(
relative_position, # shape (query_length, key_length)
bidirectional=(not self.is_decoder),
num_buckets=self.relative_attention_num_buckets,
max_distance=self.relative_attention_max_distance,
)
values = self.relative_attention_bias(relative_position_bucket) # shape (query_length, key_length, num_heads)
values = values.permute([2, 0, 1]).unsqueeze(0) # shape (1, num_heads, query_length, key_length)
return values
def forward(
self,
hidden_states,
mask=None,
key_value_states=None,
position_bias=None,
past_key_value=None,
layer_head_mask=None,
query_length=None,
use_cache=False,
output_attentions=False,
):
"""
Self-attention (if key_value_states is None) or attention over source sentence (provided by key_value_states).
"""
# Input is (batch_size, seq_length, dim)
# Mask is (batch_size, key_length) (non-causal) or (batch_size, key_length, key_length)
# past_key_value[0] is (batch_size, n_heads, q_len - 1, dim_per_head)
batch_size, seq_length = hidden_states.shape[:2]
real_seq_length = seq_length
if past_key_value is not None:
if len(past_key_value) != 2:
raise ValueError(
f"past_key_value should have 2 past states: keys and values. Got { len(past_key_value)} past states"
)
real_seq_length += past_key_value[0].shape[2] if query_length is None else query_length
key_length = real_seq_length if key_value_states is None else key_value_states.shape[1]
def shape(states):
"""projection"""
return states.view(batch_size, -1, self.n_heads, self.key_value_proj_dim).transpose(1, 2)
def unshape(states):
"""reshape"""
return states.transpose(1, 2).contiguous().view(batch_size, -1, self.inner_dim)
def project(hidden_states, proj_layer, key_value_states, past_key_value):
"""projects hidden states correctly to key/query states"""
if key_value_states is None:
# self-attn
# (batch_size, n_heads, seq_length, dim_per_head)
hidden_states = shape(proj_layer(hidden_states))
elif past_key_value is None:
# cross-attn
# (batch_size, n_heads, seq_length, dim_per_head)
hidden_states = shape(proj_layer(key_value_states))
if past_key_value is not None:
if key_value_states is None:
# self-attn
# (batch_size, n_heads, key_length, dim_per_head)
hidden_states = torch.cat([past_key_value, hidden_states], dim=2)
elif past_key_value.shape[2] != key_value_states.shape[1]:
# checking that the `sequence_length` of the `past_key_value` is the same as
# the provided `key_value_states` to support prefix tuning
# cross-attn
# (batch_size, n_heads, seq_length, dim_per_head)
hidden_states = shape(proj_layer(key_value_states))
else:
# cross-attn
hidden_states = past_key_value
return hidden_states
# get query states
query_states = shape(self.q(hidden_states)) # (batch_size, n_heads, seq_length, dim_per_head)
# get key/value states
key_states = project(
hidden_states, self.k, key_value_states, past_key_value[0] if past_key_value is not None else None
)
value_states = project(
hidden_states, self.v, key_value_states, past_key_value[1] if past_key_value is not None else None
)
# compute scores
scores = torch.matmul(
query_states, key_states.transpose(3, 2)
) # equivalent of torch.einsum("bnqd,bnkd->bnqk", query_states, key_states), compatible with onnx op>9
if position_bias is None:
if not self.has_relative_attention_bias:
position_bias = torch.zeros(
(1, self.n_heads, real_seq_length, key_length), device=scores.device, dtype=scores.dtype
)
if self.gradient_checkpointing and self.training:
position_bias.requires_grad = True
else:
position_bias = self.compute_bias(real_seq_length, key_length, device=scores.device)
# if key and values are already calculated
# we want only the last query position bias
if past_key_value is not None:
position_bias = position_bias[:, :, -hidden_states.size(1) :, :]
if mask is not None:
position_bias = position_bias + mask # (batch_size, n_heads, seq_length, key_length)
if self.pruned_heads:
mask = torch.ones(position_bias.shape[1])
mask[list(self.pruned_heads)] = 0
position_bias_masked = position_bias[:, mask.bool()]
else:
position_bias_masked = position_bias
scores += position_bias_masked
attn_weights = nn.functional.softmax(scores.float(), dim=-1).type_as(
scores
) # (batch_size, n_heads, seq_length, key_length)
attn_weights = nn.functional.dropout(
attn_weights, p=self.dropout, training=self.training
) # (batch_size, n_heads, seq_length, key_length)
# Mask heads if we want to
if layer_head_mask is not None:
attn_weights = attn_weights * layer_head_mask
attn_output = unshape(torch.matmul(attn_weights, value_states)) # (batch_size, seq_length, dim)
attn_output = self.o(attn_output)
present_key_value_state = (key_states, value_states) if (self.is_decoder and use_cache) else None
outputs = (attn_output,) + (present_key_value_state,) + (position_bias,)
if output_attentions:
outputs = outputs + (attn_weights,)
return outputs
# Copied from transformers.models.t5.modeling_t5.T5LayerSelfAttention with T5->SwitchTransformers
class SwitchTransformersLayerSelfAttention(nn.Module):
def __init__(self, config, has_relative_attention_bias=False):
super().__init__()
self.SelfAttention = SwitchTransformersAttention(
config, has_relative_attention_bias=has_relative_attention_bias
)
self.layer_norm = SwitchTransformersLayerNorm(config.d_model, eps=config.layer_norm_epsilon)
self.dropout = nn.Dropout(config.dropout_rate)
def forward(
self,
hidden_states,
attention_mask=None,
position_bias=None,
layer_head_mask=None,
past_key_value=None,
use_cache=False,
output_attentions=False,
):
normed_hidden_states = self.layer_norm(hidden_states)
attention_output = self.SelfAttention(
normed_hidden_states,
mask=attention_mask,
position_bias=position_bias,
layer_head_mask=layer_head_mask,
past_key_value=past_key_value,
use_cache=use_cache,
output_attentions=output_attentions,
)
hidden_states = hidden_states + self.dropout(attention_output[0])
outputs = (hidden_states,) + attention_output[1:] # add attentions if we output them
return outputs
# Copied from transformers.models.t5.modeling_t5.T5LayerCrossAttention with T5->SwitchTransformers
class SwitchTransformersLayerCrossAttention(nn.Module):
def __init__(self, config):
super().__init__()
self.EncDecAttention = SwitchTransformersAttention(config, has_relative_attention_bias=False)
self.layer_norm = SwitchTransformersLayerNorm(config.d_model, eps=config.layer_norm_epsilon)
self.dropout = nn.Dropout(config.dropout_rate)
def forward(
self,
hidden_states,
key_value_states,
attention_mask=None,
position_bias=None,
layer_head_mask=None,
past_key_value=None,
use_cache=False,
query_length=None,
output_attentions=False,
):
normed_hidden_states = self.layer_norm(hidden_states)
attention_output = self.EncDecAttention(
normed_hidden_states,
mask=attention_mask,
key_value_states=key_value_states,
position_bias=position_bias,
layer_head_mask=layer_head_mask,
past_key_value=past_key_value,
use_cache=use_cache,
query_length=query_length,
output_attentions=output_attentions,
)
layer_output = hidden_states + self.dropout(attention_output[0])
outputs = (layer_output,) + attention_output[1:] # add attentions if we output them
return outputs
class SwitchTransformersBlock(nn.Module):
def __init__(self, config, has_relative_attention_bias=False, is_sparse=False):
super().__init__()
self.is_decoder = config.is_decoder
self.is_sparse = is_sparse
self.layer = nn.ModuleList()
self.layer.append(
SwitchTransformersLayerSelfAttention(config, has_relative_attention_bias=has_relative_attention_bias)
)
if self.is_decoder:
self.layer.append(SwitchTransformersLayerCrossAttention(config))
self.layer.append(SwitchTransformersLayerFF(config, is_sparse=self.is_sparse))
def forward(
self,
hidden_states,
attention_mask=None,
position_bias=None,
encoder_hidden_states=None,
encoder_attention_mask=None,
encoder_decoder_position_bias=None,
layer_head_mask=None,
cross_attn_layer_head_mask=None,
past_key_value=None,
use_cache=False,
output_attentions=False,
output_router_logits=True,
return_dict=True,
):
if past_key_value is not None:
if not self.is_decoder:
logger.warning("`past_key_values` is passed to the encoder. Please make sure this is intended.")
expected_num_past_key_values = 2 if encoder_hidden_states is None else 4
if len(past_key_value) != expected_num_past_key_values:
raise ValueError(
f"There should be {expected_num_past_key_values} past states. "
f"{'2 (past / key) for cross attention. ' if expected_num_past_key_values == 4 else ''}"
f"Got {len(past_key_value)} past key / value states"
)
self_attn_past_key_value = past_key_value[:2]
cross_attn_past_key_value = past_key_value[2:]
else:
self_attn_past_key_value, cross_attn_past_key_value = None, None
self_attention_outputs = self.layer[0](
hidden_states,
attention_mask=attention_mask,
position_bias=position_bias,
layer_head_mask=layer_head_mask,
past_key_value=self_attn_past_key_value,
use_cache=use_cache,
output_attentions=output_attentions,
)
hidden_states, present_key_value_state = self_attention_outputs[:2]
attention_outputs = self_attention_outputs[2:] # Keep self-attention outputs and relative position weights
# clamp inf values to enable fp16 training
if hidden_states.dtype == torch.float16 and torch.isinf(hidden_states).any():
clamp_value = torch.finfo(hidden_states.dtype).max - 1000
hidden_states = torch.clamp(hidden_states, min=-clamp_value, max=clamp_value)
do_cross_attention = self.is_decoder and encoder_hidden_states is not None
if do_cross_attention:
# the actual query length is unknown for cross attention
# if using past key value states. Need to inject it here
if present_key_value_state is not None:
query_length = present_key_value_state[0].shape[2]
else:
query_length = None
cross_attention_outputs = self.layer[1](
hidden_states,
key_value_states=encoder_hidden_states,
attention_mask=encoder_attention_mask,
position_bias=encoder_decoder_position_bias,
layer_head_mask=cross_attn_layer_head_mask,
past_key_value=cross_attn_past_key_value,
query_length=query_length,
use_cache=use_cache,
output_attentions=output_attentions,
)
hidden_states = cross_attention_outputs[0]
# clamp inf values to enable fp16 training
if hidden_states.dtype == torch.float16 and torch.isinf(hidden_states).any():
clamp_value = torch.finfo(hidden_states.dtype).max - 1000
hidden_states = torch.clamp(hidden_states, min=-clamp_value, max=clamp_value)
# Combine self attn and cross attn key value states
if present_key_value_state is not None:
present_key_value_state = present_key_value_state + cross_attention_outputs[1]
# Keep cross-attention outputs and relative position weights
attention_outputs = attention_outputs + cross_attention_outputs[2:]
# Apply Feed Forward layer
hidden_states = self.layer[-1](hidden_states, output_router_logits)
if isinstance(hidden_states, tuple):
hidden_states, router_tuple = hidden_states
else:
router_tuple = (torch.zeros((1,), device=hidden_states.device, dtype=torch.int64),)
# clamp inf values to enable fp16 training
if hidden_states.dtype == torch.float16 and torch.isinf(hidden_states).any():
clamp_value = torch.finfo(hidden_states.dtype).max - 1000
hidden_states = torch.clamp(hidden_states, min=-clamp_value, max=clamp_value)
outputs = (hidden_states,)
if use_cache:
outputs = outputs + (present_key_value_state,) + attention_outputs + (router_tuple,)
else:
outputs = outputs + attention_outputs + (router_tuple,)
return outputs # hidden-states, present_key_value_states, (self-attention position bias), (self-attention weights), (cross-attention position bias), (cross-attention weights), (router_tuple)
class SwitchTransformersPreTrainedModel(PreTrainedModel):
"""
An abstract class to handle weights initialization and a simple interface for downloading and loading pretrained
models.
"""
config_class = SwitchTransformersConfig
base_model_prefix = "switch_transformers"
supports_gradient_checkpointing = True
_no_split_modules = ["SwitchTransformersBlock"]
@property
def dummy_inputs(self):
input_ids = torch.tensor(DUMMY_INPUTS)
input_mask = torch.tensor(DUMMY_MASK)
dummy_inputs = {
"decoder_input_ids": input_ids,
"input_ids": input_ids,
"decoder_attention_mask": input_mask,
}
return dummy_inputs
def _init_weights(self, module):
"""Initialize the weights"""
factor = self.config.initializer_factor # Used for testing weights initialization
if isinstance(module, SwitchTransformersLayerNorm):
module.weight.data.fill_(factor * 1.0)
elif isinstance(
module,
(SwitchTransformersModel, SwitchTransformersForConditionalGeneration, SwitchTransformersEncoderModel),
):
# Mesh TensorFlow embeddings initialization
# See https://github.com/tensorflow/mesh/blob/fa19d69eafc9a482aff0b59ddd96b025c0cb207d/mesh_tensorflow/layers.py#L1624
module.shared.weight.data.normal_(mean=0.0, std=factor * 1.0)
if hasattr(module, "lm_head") and not self.config.tie_word_embeddings:
module.lm_head.weight.data.normal_(mean=0.0, std=factor * 1.0)
elif isinstance(module, SwitchTransformersDenseActDense):
# Mesh TensorFlow FF initialization
# See https://github.com/tensorflow/mesh/blob/master/mesh_tensorflow/transformer/transformer_layers.py#L56
# and https://github.com/tensorflow/mesh/blob/fa19d69eafc9a482aff0b59ddd96b025c0cb207d/mesh_tensorflow/layers.py#L89
module.wi.weight.data.normal_(mean=0.0, std=factor * ((self.config.d_model) ** -0.5))
if hasattr(module.wi, "bias") and module.wi.bias is not None:
module.wi.bias.data.zero_()
module.wo.weight.data.normal_(mean=0.0, std=factor * ((self.config.d_ff) ** -0.5))
if hasattr(module.wo, "bias") and module.wo.bias is not None:
module.wo.bias.data.zero_()
elif isinstance(module, SwitchTransformersAttention):
# Mesh TensorFlow attention initialization to avoid scaling before softmax
# See https://github.com/tensorflow/mesh/blob/fa19d69eafc9a482aff0b59ddd96b025c0cb207d/mesh_tensorflow/transformer/attention.py#L136
d_model = self.config.d_model
key_value_proj_dim = self.config.d_kv
n_heads = self.config.num_heads
module.q.weight.data.normal_(mean=0.0, std=factor * ((d_model * key_value_proj_dim) ** -0.5))
module.k.weight.data.normal_(mean=0.0, std=factor * (d_model**-0.5))
module.v.weight.data.normal_(mean=0.0, std=factor * (d_model**-0.5))
module.o.weight.data.normal_(mean=0.0, std=factor * ((n_heads * key_value_proj_dim) ** -0.5))
if module.has_relative_attention_bias:
module.relative_attention_bias.weight.data.normal_(mean=0.0, std=factor * ((d_model) ** -0.5))
elif isinstance(module, SwitchTransformersSparseMLP):
# Mesh TensorFlow attention initialization to avoid scaling before softmax
# See https://github.com/tensorflow/mesh/blob/fa19d69eafc9a482aff0b59ddd96b025c0cb207d/mesh_tensorflow/transformer/attention.py#L136
d_model = self.config.d_model
key_value_proj_dim = self.config.d_kv
n_heads = self.config.num_heads
module.router.classifier.weight.data.normal_(mean=0.0, std=factor * 1)
for idx in range(self.config.num_experts):
module.experts[f"expert_{idx}"].wi.weight.data.normal_(mean=0.0, std=factor * (d_model**-0.5))
module.experts[f"expert_{idx}"].wo.weight.data.normal_(mean=0.0, std=factor * (d_model**-0.5))
def _set_gradient_checkpointing(self, module, value=False):
if isinstance(module, (SwitchTransformersAttention, SwitchTransformersStack)):
module.gradient_checkpointing = value
def _shift_right(self, input_ids):
decoder_start_token_id = self.config.decoder_start_token_id
pad_token_id = self.config.pad_token_id
if decoder_start_token_id is None:
raise ValueError(
"self.model.config.decoder_start_token_id has to be defined. In SwitchTransformers it is usually set"
" to the pad_token_id. See SwitchTransformers docs for more information"
)
# shift inputs to the right
if is_torch_fx_proxy(input_ids):
# Item assignment is not supported natively for proxies.
shifted_input_ids = torch.full(input_ids.shape[:-1] + (1,), decoder_start_token_id)
shifted_input_ids = torch.cat([shifted_input_ids, input_ids[..., :-1]], dim=-1)
else:
shifted_input_ids = input_ids.new_zeros(input_ids.shape)
shifted_input_ids[..., 1:] = input_ids[..., :-1].clone()
shifted_input_ids[..., 0] = decoder_start_token_id
if pad_token_id is None:
raise ValueError("self.model.config.pad_token_id has to be defined.")
# replace possible -100 values in labels by `pad_token_id`
shifted_input_ids.masked_fill_(shifted_input_ids == -100, pad_token_id)
return shifted_input_ids
class SwitchTransformersStack(SwitchTransformersPreTrainedModel):
def __init__(self, config, embed_tokens=None):
super().__init__(config)
self.embed_tokens = nn.Embedding(config.vocab_size, config.d_model)
if embed_tokens is not None:
self.embed_tokens.weight = embed_tokens.weight
self.is_decoder = config.is_decoder
sparse_step = config.decoder_sparse_step if self.is_decoder else config.encoder_sparse_step
config.num_layers = config.num_decoder_layers if self.is_decoder else config.num_layers
self.block = nn.ModuleList()
for i in range(config.num_layers):
is_sparse = (i % sparse_step == 1) if sparse_step > 0 else False
self.block.append(
SwitchTransformersBlock(config, has_relative_attention_bias=bool(i == 0), is_sparse=is_sparse)
)
self.final_layer_norm = SwitchTransformersLayerNorm(config.d_model, eps=config.layer_norm_epsilon)
self.dropout = nn.Dropout(config.dropout_rate)
# Initialize weights and apply final processing
self.post_init()
self.device_map = None
self.gradient_checkpointing = False
def get_input_embeddings(self):
return self.embed_tokens
def set_input_embeddings(self, new_embeddings):
self.embed_tokens = new_embeddings
def forward(
self,
input_ids=None,
attention_mask=None,
encoder_hidden_states=None,
encoder_attention_mask=None,
inputs_embeds=None,
head_mask=None,
cross_attn_head_mask=None,
past_key_values=None,
use_cache=None,
output_attentions=None,
output_hidden_states=None,
output_router_logits=True,
return_dict=None,
):
use_cache = use_cache if use_cache is not None else self.config.use_cache
output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
output_hidden_states = (
output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
)
return_dict = return_dict if return_dict is not None else self.config.use_return_dict
if input_ids is not None and inputs_embeds is not None:
err_msg_prefix = "decoder_" if self.is_decoder else ""
raise ValueError(
f"You cannot specify both {err_msg_prefix}input_ids and {err_msg_prefix}inputs_embeds at the same time"
)
elif input_ids is not None:
input_shape = input_ids.size()
input_ids = input_ids.view(-1, input_shape[-1])
elif inputs_embeds is not None:
input_shape = inputs_embeds.size()[:-1]
else:
err_msg_prefix = "decoder_" if self.is_decoder else ""
raise ValueError(f"You have to specify either {err_msg_prefix}input_ids or {err_msg_prefix}inputs_embeds")
if inputs_embeds is None:
if self.embed_tokens is None:
raise ValueError("You have to initialize the model with valid token embeddings")
inputs_embeds = self.embed_tokens(input_ids)
batch_size, seq_length = input_shape
# required mask seq length can be calculated via length of past
mask_seq_length = past_key_values[0][0].shape[2] + seq_length if past_key_values is not None else seq_length
if use_cache is True:
if not self.is_decoder:
raise ValueError(f"`use_cache` can only be set to `True` if {self} is used as a decoder")
if attention_mask is None:
attention_mask = torch.ones(batch_size, mask_seq_length, device=inputs_embeds.device)
if self.is_decoder and encoder_attention_mask is None and encoder_hidden_states is not None:
encoder_seq_length = encoder_hidden_states.shape[1]
encoder_attention_mask = torch.ones(
batch_size, encoder_seq_length, device=inputs_embeds.device, dtype=torch.long
)
# initialize past_key_values with `None` if past does not exist
if past_key_values is None:
past_key_values = [None] * len(self.block)
# We can provide a self-attention mask of dimensions [batch_size, from_seq_length, to_seq_length]
# ourselves in which case we just need to make it broadcastable to all heads.