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"""A simple, flexible implementation of a GPT model. |
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Inspired by https://github.com/karpathy/minGPT/blob/master/mingpt/model.py |
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""" |
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import math |
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import warnings |
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from typing import List, Optional, Tuple, Union |
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import torch |
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import torch.nn as nn |
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import torch.nn.functional as F |
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from transformers import PreTrainedModel, PreTrainedTokenizer, PreTrainedTokenizerFast |
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from transformers.modeling_outputs import BaseModelOutputWithPast, CausalLMOutputWithPast |
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from .attention import attn_bias_shape, build_attn_bias |
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from .blocks import MPTBlock |
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from .norm import NORM_CLASS_REGISTRY |
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from .configuration_mpt import MPTConfig |
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from .adapt_tokenizer import AutoTokenizerForMOD, adapt_tokenizer_for_denoising |
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from .hf_prefixlm_converter import add_bidirectional_mask_if_missing, convert_hf_causal_lm_to_prefix_lm |
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from .meta_init_context import init_empty_weights |
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from .param_init_fns import MODEL_INIT_REGISTRY, generic_param_init_fn_ |
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Tokenizer = Union[PreTrainedTokenizer, PreTrainedTokenizerFast] |
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class MPTPreTrainedModel(PreTrainedModel): |
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config_class = MPTConfig |
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base_model_prefix = 'model' |
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_no_split_modules=["MPTBlock"] |
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class MPTModel(MPTPreTrainedModel): |
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def __init__(self, config: MPTConfig): |
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config._validate_config() |
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super().__init__(config) |
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self.attn_impl = config.attn_config['attn_impl'] |
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self.prefix_lm = config.attn_config['prefix_lm'] |
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self.attn_uses_sequence_id = config.attn_config['attn_uses_sequence_id'] |
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self.alibi = config.attn_config['alibi'] |
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self.alibi_bias_max = config.attn_config['alibi_bias_max'] |
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if config.norm_type.lower() not in NORM_CLASS_REGISTRY.keys(): |
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norm_options = ' | '.join(NORM_CLASS_REGISTRY.keys()) |
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raise NotImplementedError(f'Requested norm type ({config.norm_type}) is not implemented within this repo (Options: {norm_options}).') |
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norm_class = NORM_CLASS_REGISTRY[config.norm_type.lower()] |
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self.embedding_fraction = config.embedding_fraction |
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self.wte = nn.Embedding(config.vocab_size, config.d_model, device=config.init_device) |
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if not self.alibi: |
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self.wpe = nn.Embedding(config.max_seq_len, config.d_model, device=config.init_device) |
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self.emb_drop = nn.Dropout(config.emb_pdrop) |
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self.blocks = nn.ModuleList([MPTBlock(device=config.init_device, **config.to_dict()) for _ in range(config.n_layers)]) |
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self.norm_f = norm_class(config.d_model, device=config.init_device) |
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if config.init_device != 'meta': |
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print(f'You are using config.init_device={config.init_device!r}, but you can also use config.init_device="meta" with Composer + FSDP for fast initialization.') |
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self.apply(self.param_init_fn) |
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self.is_causal = not self.prefix_lm |
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self._attn_bias_initialized = False |
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self.attn_bias = None |
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self.attn_bias_shape = attn_bias_shape(self.attn_impl, config.n_heads, config.max_seq_len, self.alibi, prefix_lm=self.prefix_lm, causal=self.is_causal, use_sequence_id=self.attn_uses_sequence_id) |
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if config.no_bias: |
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for module in self.modules(): |
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if hasattr(module, 'bias') and isinstance(module.bias, nn.Parameter): |
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if config.verbose: |
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warnings.warn(f'Removing bias ({module.bias}) from {module}.') |
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module.register_parameter('bias', None) |
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if config.verbose and config.verbose > 2: |
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print(self) |
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if 'verbose' not in self.config.init_config: |
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self.config.init_config['verbose'] = self.config.verbose |
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if self.config.init_config['verbose'] > 1: |
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init_fn_name = self.config.init_config['name'] |
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warnings.warn(f'Using {init_fn_name} initialization.') |
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def get_input_embeddings(self): |
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return self.wte |
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def set_input_embeddings(self, value): |
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self.wte = value |
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@torch.no_grad() |
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def _attn_bias(self, device, dtype, attention_mask: Optional[torch.ByteTensor]=None, prefix_mask: Optional[torch.ByteTensor]=None, sequence_id: Optional[torch.LongTensor]=None): |
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if not self._attn_bias_initialized: |
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if self.attn_bias_shape: |
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self.attn_bias = torch.zeros(self.attn_bias_shape, device=device, dtype=dtype) |
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self.attn_bias = build_attn_bias(self.attn_impl, self.attn_bias, self.config.n_heads, self.config.max_seq_len, causal=self.is_causal, alibi=self.alibi, alibi_bias_max=self.alibi_bias_max) |
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self._attn_bias_initialized = True |
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if self.attn_impl == 'flash': |
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return (self.attn_bias, attention_mask) |
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if self.attn_bias is not None: |
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self.attn_bias = self.attn_bias.to(dtype=dtype, device=device) |
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attn_bias = self.attn_bias |
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if self.prefix_lm: |
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assert isinstance(attn_bias, torch.Tensor) |
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assert isinstance(prefix_mask, torch.Tensor) |
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attn_bias = self._apply_prefix_mask(attn_bias, prefix_mask) |
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if self.attn_uses_sequence_id and sequence_id is not None: |
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assert isinstance(attn_bias, torch.Tensor) |
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attn_bias = self._apply_sequence_id(attn_bias, sequence_id) |
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if attention_mask is not None: |
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s_k = attention_mask.shape[-1] |
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if attn_bias is None: |
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attn_bias = torch.zeros((1, 1, 1, s_k), device=device, dtype=dtype) |
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else: |
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attn_bias = attn_bias[:, :, :, -s_k:] |
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if prefix_mask is not None and attention_mask.shape != prefix_mask.shape: |
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raise ValueError(f'attention_mask shape={attention_mask.shape} ' + f'and prefix_mask shape={prefix_mask.shape} are not equal.') |
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min_val = torch.finfo(attn_bias.dtype).min |
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attn_bias = attn_bias.masked_fill(~attention_mask.view(-1, 1, 1, s_k), min_val) |
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return (attn_bias, None) |
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def _apply_prefix_mask(self, attn_bias: torch.Tensor, prefix_mask: torch.Tensor): |
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(s_k, s_q) = attn_bias.shape[-2:] |
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if s_k != self.config.max_seq_len or s_q != self.config.max_seq_len: |
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raise ValueError('attn_bias does not match the expected shape. ' + f'The last two dimensions should both be {self.config.max_length} ' + f'but are {s_k} and {s_q}.') |
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seq_len = prefix_mask.shape[-1] |
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if seq_len > self.config.max_seq_len: |
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raise ValueError(f'prefix_mask sequence length cannot exceed max_seq_len={self.config.max_seq_len}') |
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attn_bias = attn_bias[..., :seq_len, :seq_len] |
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causal = torch.tril(torch.ones((seq_len, seq_len), dtype=torch.bool, device=prefix_mask.device)).view(1, 1, seq_len, seq_len) |
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prefix = prefix_mask.view(-1, 1, 1, seq_len) |
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cannot_attend = ~torch.logical_or(causal, prefix.bool()) |
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min_val = torch.finfo(attn_bias.dtype).min |
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attn_bias = attn_bias.masked_fill(cannot_attend, min_val) |
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return attn_bias |
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def _apply_sequence_id(self, attn_bias: torch.Tensor, sequence_id: torch.LongTensor): |
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seq_len = sequence_id.shape[-1] |
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if seq_len > self.config.max_seq_len: |
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raise ValueError(f'sequence_id sequence length cannot exceed max_seq_len={self.config.max_seq_len}') |
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attn_bias = attn_bias[..., :seq_len, :seq_len] |
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cannot_attend = torch.logical_not(torch.eq(sequence_id.view(-1, seq_len, 1), sequence_id.view(-1, 1, seq_len))).unsqueeze(1) |
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min_val = torch.finfo(attn_bias.dtype).min |
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attn_bias = attn_bias.masked_fill(cannot_attend, min_val) |
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return attn_bias |
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def forward(self, input_ids: torch.LongTensor, past_key_values: Optional[List[Tuple[torch.FloatTensor]]]=None, attention_mask: Optional[torch.ByteTensor]=None, prefix_mask: Optional[torch.ByteTensor]=None, sequence_id: Optional[torch.LongTensor]=None, return_dict: Optional[bool]=None, output_attentions: Optional[bool]=None, output_hidden_states: Optional[bool]=None, use_cache: Optional[bool]=None): |
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return_dict = return_dict if return_dict is not None else self.config.return_dict |
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use_cache = use_cache if use_cache is not None else self.config.use_cache |
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if attention_mask is not None: |
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attention_mask = attention_mask.bool() |
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if prefix_mask is not None: |
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prefix_mask = prefix_mask.bool() |
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if not return_dict: |
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raise NotImplementedError('return_dict False is not implemented yet for MPT') |
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if output_attentions: |
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raise NotImplementedError('output_attentions is not implemented yet for MPT') |
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if attention_mask is not None and attention_mask[:, 0].sum() != attention_mask.shape[0] and self.training: |
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raise NotImplementedError('MPT does not support training with left padding.') |
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if self.prefix_lm and prefix_mask is None: |
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raise ValueError('prefix_mask is a required argument when MPT is configured with prefix_lm=True.') |
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if self.training: |
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if self.attn_uses_sequence_id and sequence_id is None: |
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raise ValueError('sequence_id is a required argument when MPT is configured with attn_uses_sequence_id=True ' + 'and the model is in train mode.') |
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elif self.attn_uses_sequence_id is False and sequence_id is not None: |
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warnings.warn('MPT received non-None input for `sequence_id` but is configured with attn_uses_sequence_id=False. ' + 'This input will be ignored. If you want the model to use `sequence_id`, set attn_uses_sequence_id to True.') |
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S = input_ids.size(1) |
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assert S <= self.config.max_seq_len, f'Cannot forward input with seq_len={S}, this model only supports seq_len<={self.config.max_seq_len}' |
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tok_emb = self.wte(input_ids) |
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if self.alibi: |
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x = tok_emb |
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else: |
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past_position = 0 |
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if past_key_values is not None: |
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if len(past_key_values) != self.config.n_layers: |
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raise ValueError(f'past_key_values must provide a past_key_value for each attention ' + f'layer in the network (len(past_key_values)={len(past_key_values)!r}; self.config.n_layers={self.config.n_layers!r}).') |
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past_position = past_key_values[0][0].size(1) |
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if S + past_position > self.config.max_seq_len: |
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raise ValueError(f'Cannot forward input with past sequence length {past_position} and current sequence length {S + 1}, this model only supports total sequence length <= {self.config.max_seq_len}.') |
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pos = torch.arange(past_position, S + past_position, dtype=torch.long, device=input_ids.device).unsqueeze(0) |
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if attention_mask is not None: |
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pos = torch.clamp(pos - torch.cumsum((~attention_mask).to(torch.int32), dim=1)[:, past_position:], min=0) |
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pos_emb = self.wpe(pos) |
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x = tok_emb + pos_emb |
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if self.embedding_fraction == 1: |
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x = self.emb_drop(x) |
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else: |
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x_shrunk = x * self.embedding_fraction + x.detach() * (1 - self.embedding_fraction) |
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assert isinstance(self.emb_drop, nn.Module) |
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x = self.emb_drop(x_shrunk) |
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(attn_bias, attention_mask) = self._attn_bias(device=x.device, dtype=x.dtype, attention_mask=attention_mask, prefix_mask=prefix_mask, sequence_id=sequence_id) |
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if use_cache and past_key_values is None: |
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past_key_values = [() for _ in range(self.config.n_layers)] |
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all_hidden_states = () if output_hidden_states else None |
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for (b_idx, block) in enumerate(self.blocks): |
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if output_hidden_states: |
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assert all_hidden_states is not None |
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all_hidden_states = all_hidden_states + (x,) |
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past_key_value = past_key_values[b_idx] if past_key_values is not None else None |
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(x, past_key_value) = block(x, past_key_value=past_key_value, attn_bias=attn_bias, attention_mask=attention_mask, is_causal=self.is_causal) |
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if past_key_values is not None: |
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past_key_values[b_idx] = past_key_value |
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x = self.norm_f(x) |
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return BaseModelOutputWithPast(last_hidden_state=x, past_key_values=past_key_values, hidden_states=all_hidden_states) |
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def param_init_fn(self, module): |
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init_fn_name = self.config.init_config['name'] |
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MODEL_INIT_REGISTRY[init_fn_name](module=module, n_layers=self.config.n_layers, d_model=self.config.d_model, **self.config.init_config) |
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def fsdp_wrap_fn(self, module): |
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return isinstance(module, MPTBlock) |
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def activation_checkpointing_fn(self, module): |
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return isinstance(module, MPTBlock) |
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class MPTForCausalLM(MPTPreTrainedModel): |
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def __init__(self, config: MPTConfig): |
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super().__init__(config) |
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if not config.tie_word_embeddings: |
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raise ValueError('MPTForCausalLM only supports tied word embeddings') |
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self.transformer = MPTModel(config) |
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self.logit_scale = None |
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if config.logit_scale is not None: |
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logit_scale = config.logit_scale |
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if isinstance(logit_scale, str): |
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if logit_scale == 'inv_sqrt_d_model': |
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logit_scale = 1 / math.sqrt(config.d_model) |
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else: |
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raise ValueError(f"logit_scale={logit_scale!r} is not recognized as an option; use numeric value or 'inv_sqrt_d_model'.") |
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self.logit_scale = logit_scale |
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def get_input_embeddings(self): |
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return self.transformer.wte |
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def set_input_embeddings(self, value): |
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self.transformer.wte = value |
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def get_output_embeddings(self): |
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return self.transformer.wte |
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def set_output_embeddings(self, new_embeddings): |
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self.transformer.wte = new_embeddings |
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def set_decoder(self, decoder): |
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self.transformer = decoder |
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def get_decoder(self): |
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return self.transformer |
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def forward(self, input_ids: torch.LongTensor, past_key_values: Optional[List[Tuple[torch.FloatTensor]]]=None, attention_mask: Optional[torch.ByteTensor]=None, prefix_mask: Optional[torch.ByteTensor]=None, sequence_id: Optional[torch.LongTensor]=None, labels: Optional[torch.LongTensor]=None, return_dict: Optional[bool]=None, output_attentions: Optional[bool]=None, output_hidden_states: Optional[bool]=None, use_cache: Optional[bool]=None): |
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return_dict = return_dict if return_dict is not None else self.config.return_dict |
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use_cache = use_cache if use_cache is not None else self.config.use_cache |
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outputs = self.transformer(input_ids=input_ids, past_key_values=past_key_values, attention_mask=attention_mask, prefix_mask=prefix_mask, sequence_id=sequence_id, return_dict=return_dict, output_attentions=output_attentions, output_hidden_states=output_hidden_states, use_cache=use_cache) |
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logits = F.linear(outputs.last_hidden_state, self.transformer.wte.weight) |
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if self.logit_scale is not None: |
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if self.logit_scale == 0: |
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warnings.warn(f'Multiplying logits by self.logit_scale={self.logit_scale!r}. This will produce uniform (uninformative) outputs.') |
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logits *= self.logit_scale |
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loss = None |
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if labels is not None: |
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labels = torch.roll(labels, shifts=-1) |
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labels[:, -1] = -100 |
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loss = F.cross_entropy(logits.view(-1, logits.size(-1)), labels.to(logits.device).view(-1)) |
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return CausalLMOutputWithPast(loss=loss, logits=logits, past_key_values=outputs.past_key_values, hidden_states=outputs.hidden_states) |
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def param_init_fn(self, module): |
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init_fn_name = self.config.init_config['name'] |
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MODEL_INIT_REGISTRY[init_fn_name](module=module, n_layers=self.config.n_layers, d_model=self.config.d_model, **self.config.init_config) |
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def fsdp_wrap_fn(self, module): |
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return isinstance(module, MPTBlock) |
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def activation_checkpointing_fn(self, module): |
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return isinstance(module, MPTBlock) |
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def prepare_inputs_for_generation(self, input_ids, past_key_values=None, inputs_embeds=None, **kwargs): |
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if inputs_embeds is not None: |
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raise NotImplementedError('inputs_embeds is not implemented for MPT yet') |
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attention_mask = kwargs['attention_mask'].bool() |
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if attention_mask[:, -1].sum() != attention_mask.shape[0]: |
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raise NotImplementedError('MPT does not support generation with right padding.') |
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if self.transformer.attn_uses_sequence_id and self.training: |
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sequence_id = torch.zeros_like(input_ids[:1]) |
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else: |
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sequence_id = None |
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if past_key_values is not None: |
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input_ids = input_ids[:, -1].unsqueeze(-1) |
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if self.transformer.prefix_lm: |
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prefix_mask = torch.ones_like(attention_mask) |
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if kwargs.get('use_cache') == False: |
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raise NotImplementedError('MPT with prefix_lm=True does not support use_cache=False.') |
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else: |
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prefix_mask = None |
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return {'input_ids': input_ids, 'attention_mask': attention_mask, 'prefix_mask': prefix_mask, 'sequence_id': sequence_id, 'past_key_values': past_key_values, 'use_cache': kwargs.get('use_cache', True)} |
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@staticmethod |
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def _reorder_cache(past_key_values, beam_idx): |
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"""Used by HuggingFace generate when using beam search with kv-caching. |
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See https://github.com/huggingface/transformers/blob/3ec7a47664ebe40c40f4b722f6bb1cd30c3821ec/src/transformers/models/gpt2/modeling_gpt2.py#L1122-L1133 |
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for an example in transformers. |
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""" |
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reordered_past = [] |
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for layer_past in past_key_values: |
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reordered_past += [tuple((past_state.index_select(0, beam_idx) for past_state in layer_past))] |
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return reordered_past |
