model.py

# !/usr/bin/env python
# -*-coding:utf-8 -*-

"""
# Time       ：2024/10/16 19:28
# Author     ：Maxwell
# Description：
"""
import math
from typing import Any, Optional, Tuple
import torch
import torch.nn.functional as F
from torch import nn
from transformers import PreTrainedModel
from transformers.modeling_outputs import CausalLMOutputWithPast
from transformers import PretrainedConfig


class LMConfig(PretrainedConfig):
    model_type = "minimind"

    def __init__(
            self,
            dim: int = 512,  # 模型的隐藏维度，即每个层的输出向量的大小
            n_layers: int = 8,  # Transformer 模型中的层数
            n_heads: int = 16,  # 多头注意力机制中的注意力头数
            n_kv_heads: int = 8,  # 键和值所使用的注意力头数
            vocab_size: int = 6400,  # 词汇表的大小
            hidden_dim: int = None,  # 前馈神经网络层的隐藏层维度
            multiple_of: int = 64,  # 用于计算隐藏层维度的倍数
            norm_eps: float = 1e-5,  # 归一化层中的 epsilon 值
            max_seq_len: int = 512,  # 模型支持的最大序列长度
            dropout: float = 0.0,  # dropout 概率，用于防止过拟合
            flash_attn: bool = True,  # 是否使用闪存注意力

            # 下面是门控专家（MoE）特定的参数
            use_moe: bool = False,  # 是否启用门控专家机制（MoE）
            num_experts_per_tok=2,  # 每个标记选择的专家数量
            n_routed_experts=4,  # 总的专家数量
            n_shared_experts: bool = True,  # 是否使用共享专家
            scoring_func='softmax',  # 用于选择专家的评分函数
            aux_loss_alpha=0.01,  # 辅助损失的 alpha 参数
            seq_aux=True,  # 是否在序列级别上计算辅助损失
            norm_topk_prob=True,  # 是否标准化 top-k 概率
            **kwargs,
    ):
        self.dim = dim
        self.n_layers = n_layers
        self.n_heads = n_heads
        self.n_kv_heads = n_kv_heads
        self.vocab_size = vocab_size
        self.hidden_dim = hidden_dim
        self.multiple_of = multiple_of
        self.norm_eps = norm_eps
        self.max_seq_len = max_seq_len
        self.dropout = dropout
        self.flash_attn = flash_attn

        # 下面是门控专家（MoE）特定的配置
        self.use_moe = use_moe
        self.num_experts_per_tok = num_experts_per_tok
        self.n_routed_experts = n_routed_experts
        self.n_shared_experts = n_shared_experts
        self.scoring_func = scoring_func
        self.aux_loss_alpha = aux_loss_alpha
        self.seq_aux = seq_aux
        self.norm_topk_prob = norm_topk_prob
        super().__init__(**kwargs)


class RMSNorm(torch.nn.Module):

    """
    实现了 RMSNorm（Root Mean Square Normalization），用于对输入进行归一化。
    计算输入的均方根，并进行标准化处理。
    """

    def __init__(self, dim: int, eps: float):
        super().__init__()
        self.eps = eps
        self.weight = nn.Parameter(torch.ones(dim))

    def _norm(self, x):
        return x * torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + self.eps)

    def forward(self, x):
        output = self._norm(x.float()).type_as(x)
        return output * self.weight


def precompute_pos_cis(dim: int, end: int, theta: float = 10000.0, train_len: int = 512):
    """
    预计算位置编码，使用复数形式表示位置编码以支持旋转嵌入（rotary embeddings）。
    """
    freqs = 1.0 / (theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim))
    t = torch.arange(end, device=freqs.device)  # type: ignore
    freqs = torch.outer(t, freqs).float()  # type: ignore
    pos_cis = torch.polar(torch.ones_like(freqs), freqs)  # complex64
    # 计算缩放因子
    # scale = train_len / end
    # 缩放旋转嵌入，实现线性的长度外推（注释掉不用是因为小模型依赖pos_cis拟合严重，直接做线性外推效果并不好）
    # pos_cis = pos_cis * scale
    return pos_cis


def apply_rotary_emb(xq, xk, pos_cis):
    """
    应用旋转嵌入，通过复数运算实现位置编码的旋转。
    :param xq:
    :param xk:
    :param pos_cis:
    :return:
    """
    def unite_shape(pos_cis, x):
        ndim = x.ndim
        assert 0 <= 1 < ndim
        assert pos_cis.shape == (x.shape[1], x.shape[-1])
        shape = [d if i == 1 or i == ndim - 1 else 1 for i, d in enumerate(x.shape)]
        return pos_cis.view(*shape)

    xq_ = torch.view_as_complex(xq.float().reshape(*xq.shape[:-1], -1, 2))
    xk_ = torch.view_as_complex(xk.float().reshape(*xk.shape[:-1], -1, 2))
    pos_cis = unite_shape(pos_cis, xq_)
    xq_out = torch.view_as_real(xq_ * pos_cis).flatten(3)
    xk_out = torch.view_as_real(xk_ * pos_cis).flatten(3)
    return xq_out.type_as(xq), xk_out.type_as(xk)


def repeat_kv(x: torch.Tensor, n_rep: int) -> torch.Tensor:
    """torch.repeat_interleave(x, dim=2, repeats=n_rep)"""
    bs, slen, n_kv_heads, head_dim = x.shape
    if n_rep == 1:
        return x
    return (
        x[:, :, :, None, :]
        .expand(bs, slen, n_kv_heads, n_rep, head_dim)
        .reshape(bs, slen, n_kv_heads * n_rep, head_dim)
    )


class Attention(nn.Module):

    """
    实现多头注意力机制。
    包括查询（query）、键（key）、值（value）线性变换，掩码机制，注意力得分计算等。
    """

    def __init__(self, args: LMConfig):
        super().__init__()
        self.n_kv_heads = args.n_heads if args.n_kv_heads is None else args.n_kv_heads
        assert args.n_heads % self.n_kv_heads == 0
        self.n_local_heads = args.n_heads
        self.n_local_kv_heads = self.n_kv_heads
        self.n_rep = self.n_local_heads // self.n_local_kv_heads
        self.head_dim = args.dim // args.n_heads
        self.wq = nn.Linear(args.dim, args.n_heads * self.head_dim, bias=False)
        self.wk = nn.Linear(args.dim, self.n_kv_heads * self.head_dim, bias=False)
        self.wv = nn.Linear(args.dim, self.n_kv_heads * self.head_dim, bias=False)
        self.wo = nn.Linear(args.n_heads * self.head_dim, args.dim, bias=False)
        self.k_cache, self.v_cache = None, None
        self.attn_dropout = nn.Dropout(args.dropout)
        self.resid_dropout = nn.Dropout(args.dropout)
        self.dropout = args.dropout
        self.flash = hasattr(torch.nn.functional, 'scaled_dot_product_attention') and args.flash_attn

        # print("WARNING: using slow attention. Flash Attention requires PyTorch >= 2.0")
        mask = torch.full((1, 1, args.max_seq_len, args.max_seq_len), float("-inf"))
        mask = torch.triu(mask, diagonal=1)
        self.register_buffer("mask", mask, persistent=False)

    def forward(self, x: torch.Tensor, pos_cis: torch.Tensor, kv_cache=False):
        bsz, seqlen, _ = x.shape

        xq, xk, xv = self.wq(x), self.wk(x), self.wv(x)

        xq = xq.view(bsz, seqlen, self.n_local_heads, self.head_dim)
        xk = xk.view(bsz, seqlen, self.n_local_kv_heads, self.head_dim)
        xv = xv.view(bsz, seqlen, self.n_local_kv_heads, self.head_dim)

        xq, xk = apply_rotary_emb(xq, xk, pos_cis)

        # 更高效的kv_cache实现
        if kv_cache and self.eval():
            if seqlen == 1 and all(cache is not None for cache in (self.k_cache, self.v_cache)):
                xk = torch.cat((self.k_cache, xk), dim=1)
                xv = torch.cat((self.v_cache, xv), dim=1)
            self.k_cache, self.v_cache = xk, xv

        xk = repeat_kv(xk, self.n_rep)  # (bs, seqlen, n_local_heads, head_dim)
        xv = repeat_kv(xv, self.n_rep)  # (bs, seqlen, n_local_heads, head_dim)

        xq = xq.transpose(1, 2)
        xk = xk.transpose(1, 2)
        xv = xv.transpose(1, 2)

        if self.flash and seqlen != 1:
            output = torch.nn.functional.scaled_dot_product_attention(xq, xk, xv, attn_mask=None,
                                                                      dropout_p=self.dropout if self.training else 0.0,
                                                                      is_causal=True)
        else:
            scores = torch.matmul(xq, xk.transpose(2, 3)) / math.sqrt(self.head_dim)
            scores = scores + self.mask[:, :, :seqlen, :seqlen]  # (bs, n_local_heads, seqlen, cache_len + seqlen)
            scores = F.softmax(scores.float(), dim=-1).type_as(xq)
            scores = self.attn_dropout(scores)
            output = torch.matmul(scores, xv)  # (bs, n_local_heads, seqlen, head_dim)

        output = output.transpose(1, 2).contiguous().view(bsz, seqlen, -1)

        output = self.wo(output)
        output = self.resid_dropout(output)
        return output


class FeedForward(nn.Module):
    """
    实现前馈神经网络层，包含两个线性变换和一个激活函数（SiLU）。
    """
    def __init__(self, dim: int, hidden_dim: int, multiple_of: int, dropout: float):
        super().__init__()
        if hidden_dim is None:
            hidden_dim = 4 * dim
            hidden_dim = int(2 * hidden_dim / 3)
            hidden_dim = multiple_of * ((hidden_dim + multiple_of - 1) // multiple_of)
        self.w1 = nn.Linear(dim, hidden_dim, bias=False)
        self.w2 = nn.Linear(hidden_dim, dim, bias=False)
        self.w3 = nn.Linear(dim, hidden_dim, bias=False)
        self.dropout = nn.Dropout(dropout)

    def forward(self, x):
        return self.dropout(self.w2(F.silu(self.w1(x)) * self.w3(x)))


class MoEGate(nn.Module):

    """
    实现门控专家机制（Mixture of Experts），根据输入选择不同的专家网络进行计算。
    包含门控机制用于选择专家，和计算辅助损失（auxiliary loss）。
    """
    def __init__(self, config: LMConfig):
        super().__init__()
        self.config = config
        self.top_k = config.num_experts_per_tok
        self.n_routed_experts = config.n_routed_experts

        self.scoring_func = config.scoring_func
        self.alpha = config.aux_loss_alpha
        self.seq_aux = config.seq_aux

        self.norm_topk_prob = config.norm_topk_prob
        self.gating_dim = config.dim
        self.weight = nn.Parameter(torch.empty((self.n_routed_experts, self.gating_dim)))
        self.reset_parameters()

    def reset_parameters(self) -> None:
        import torch.nn.init as init
        init.kaiming_uniform_(self.weight, a=math.sqrt(5))

    def forward(self, hidden_states):
        bsz, seq_len, h = hidden_states.shape

        hidden_states = hidden_states.view(-1, h)
        logits = F.linear(hidden_states, self.weight, None)
        if self.scoring_func == 'softmax':
            scores = logits.softmax(dim=-1)
        else:
            raise NotImplementedError(f'insupportable scoring function for MoE gating: {self.scoring_func}')

        topk_weight, topk_idx = torch.topk(scores, k=self.top_k, dim=-1, sorted=False)

        if self.top_k > 1 and self.norm_topk_prob:
            denominator = topk_weight.sum(dim=-1, keepdim=True) + 1e-20
            topk_weight = topk_weight / denominator

        if self.training and self.alpha > 0.0:
            scores_for_aux = scores
            aux_topk = self.top_k
            topk_idx_for_aux_loss = topk_idx.view(bsz, -1)
            if self.seq_aux:
                scores_for_seq_aux = scores_for_aux.view(bsz, seq_len, -1)
                ce = torch.zeros(bsz, self.n_routed_experts, device=hidden_states.device)
                ce.scatter_add_(1, topk_idx_for_aux_loss,
                                torch.ones(bsz, seq_len * aux_topk, device=hidden_states.device)).div_(
                    seq_len * aux_topk / self.n_routed_experts)
                aux_loss = (ce * scores_for_seq_aux.mean(dim=1)).sum(dim=1).mean() * self.alpha
            else:
                mask_ce = F.one_hot(topk_idx_for_aux_loss.view(-1), num_classes=self.n_routed_experts)
                ce = mask_ce.float().mean(0)
                Pi = scores_for_aux.mean(0)
                fi = ce * self.n_routed_experts
                aux_loss = (Pi * fi).sum() * self.alpha
        else:
            aux_loss = None
        return topk_idx, topk_weight, aux_loss


class MOEFeedForward(nn.Module):

    def __init__(self, config: LMConfig):
        super().__init__()
        self.config = config
        self.experts = nn.ModuleList([
            FeedForward(
                dim=config.dim,
                hidden_dim=config.hidden_dim,
                multiple_of=config.multiple_of,
                dropout=config.dropout,
            )
            for _ in range(config.n_routed_experts)
        ])

        self.gate = MoEGate(config)
        if config.n_shared_experts is not None:
            self.shared_experts = FeedForward(
                dim=config.dim,
                hidden_dim=config.hidden_dim,
                multiple_of=config.multiple_of,
                dropout=config.dropout,
            )

    def forward(self, x):
        identity = x
        orig_shape = x.shape
        bsz, seq_len, _ = x.shape

        # 使用门控机制选择专家
        topk_idx, topk_weight, aux_loss = self.gate(x)

        x = x.view(-1, x.shape[-1])
        flat_topk_idx = topk_idx.view(-1)

        if self.training:
            # 训练模式下，重复输入数据
            x = x.repeat_interleave(self.config.num_experts_per_tok, dim=0)
            y = torch.empty_like(x, dtype=torch.float16)
            for i, expert in enumerate(self.experts):
                y[flat_topk_idx == i] = expert(x[flat_topk_idx == i])
            y = (y.view(*topk_weight.shape, -1) * topk_weight.unsqueeze(-1)).sum(dim=1)
            y = y.view(*orig_shape)
        else:
            # 推理模式下，只选择最优专家
            y = self.moe_infer(x, flat_topk_idx, topk_weight.view(-1, 1)).view(*orig_shape)

        if self.config.n_shared_experts is not None:
            y = y + self.shared_experts(identity)

        return y

    @torch.no_grad()
    def moe_infer(self, x, flat_expert_indices, flat_expert_weights):
        expert_cache = torch.zeros_like(x)
        idxs = flat_expert_indices.argsort()
        tokens_per_expert = flat_expert_indices.bincount().cpu().numpy().cumsum(0)
        token_idxs = idxs // self.config.num_experts_per_tok
        # 例如当tokens_per_expert=[6, 15, 20, 26, 33, 38, 46, 52]
        # 当token_idxs=[3, 7, 19, 21, 24, 25,  4,  5,  6, 10, 11, 12...]
        # 意味着当token_idxs[:6] -> [3,  7, 19, 21, 24, 25,  4]位置的token都由专家0处理，token_idxs[6:15]位置的token都由专家1处理......
        for i, end_idx in enumerate(tokens_per_expert):
            start_idx = 0 if i == 0 else tokens_per_expert[i - 1]
            if start_idx == end_idx:
                continue
            expert = self.experts[i]
            exp_token_idx = token_idxs[start_idx:end_idx]
            expert_tokens = x[exp_token_idx]
            expert_out = expert(expert_tokens)
            expert_out.mul_(flat_expert_weights[idxs[start_idx:end_idx]])
            # 使用 scatter_add_ 进行 sum 操作
            expert_cache.scatter_add_(0, exp_token_idx.view(-1, 1).repeat(1, x.shape[-1]), expert_out)

        return expert_cache


class TransformerBlock(nn.Module):

    """
    组合注意力层和前馈层，构成 Transformer 的基本构建块。
    使用 RMSNorm 进行层归一化。
    """
    def __init__(self, layer_id: int, args: LMConfig):
        super().__init__()
        self.n_heads = args.n_heads
        self.dim = args.dim
        self.head_dim = args.dim // args.n_heads
        self.attention = Attention(args)

        self.layer_id = layer_id
        self.attention_norm = RMSNorm(args.dim, eps=args.norm_eps)
        self.ffn_norm = RMSNorm(args.dim, eps=args.norm_eps)

        if args.use_moe:
            self.feed_forward = MOEFeedForward(args)
        else:
            self.feed_forward = FeedForward(
                dim=args.dim,
                hidden_dim=args.hidden_dim,
                multiple_of=args.multiple_of,
                dropout=args.dropout,
            )

    def forward(self, x, pos_cis, kv_cache=False):
        h = x + self.attention(self.attention_norm(x), pos_cis, kv_cache)
        out = h + self.feed_forward(self.ffn_norm(h))
        return out


class Transformer(PreTrainedModel):
    """
    主模型类，继承自 PreTrainedModel。
    包含嵌入层、多个 Transformer 块、输出层。
    支持生成文本、评估答案、处理输入输出。
    """

    config_class = LMConfig
    last_loss: Optional[torch.Tensor]

    def __init__(self, params: LMConfig = None):
        super().__init__(params)
        if not params:
            params = LMConfig()
        self.params = params
        self.vocab_size = params.vocab_size
        self.n_layers = params.n_layers

        self.tok_embeddings = nn.Embedding(params.vocab_size, params.dim)
        self.dropout = nn.Dropout(params.dropout)
        self.layers = torch.nn.ModuleList()
        for layer_id in range(self.n_layers):
            self.layers.append(TransformerBlock(layer_id, params))
        self.norm = RMSNorm(params.dim, eps=params.norm_eps)
        self.output = nn.Linear(params.dim, params.vocab_size, bias=False)
        self.tok_embeddings.weight = self.output.weight
        pos_cis = precompute_pos_cis(self.params.dim // self.params.n_heads, self.params.max_seq_len)
        self.register_buffer("pos_cis", pos_cis, persistent=False)

        self.apply(self._init_weights)

        for pn, p in self.named_parameters():
            if pn.endswith('w3.weight') or pn.endswith('wo.weight'):
                torch.nn.init.normal_(p, mean=0.0, std=0.02 / math.sqrt(2 * params.n_layers))

        self.last_loss = None
        self.OUT = CausalLMOutputWithPast()
        self._no_split_modules = [name for name, _ in self.named_modules()]

    def _init_weights(self, module):
        if isinstance(module, nn.Linear):
            torch.nn.init.normal_(module.weight, mean=0.0, std=0.02)
            if module.bias is not None:
                torch.nn.init.zeros_(module.bias)
        elif isinstance(module, nn.Embedding):
            torch.nn.init.normal_(module.weight, mean=0.0, std=0.02)

    def forward(self, tokens: Optional[torch.Tensor] = None, targets: Optional[torch.Tensor] = None,
                kv_cache=False, **keyargs):
        current_idx = 0
        if 'input_ids' in keyargs:
            tokens = keyargs['input_ids']
        if 'attention_mask' in keyargs:
            targets = keyargs['attention_mask']
        if 'current_idx' in keyargs:
            current_idx = int(keyargs['current_idx'])

        _bsz, seqlen = tokens.shape
        h = self.tok_embeddings(tokens)
        h = self.dropout(h)
        pos_cis = self.pos_cis[current_idx:current_idx + seqlen]
        for idx, layer in enumerate(self.layers):
            h = layer(h, pos_cis, kv_cache)

        h = self.norm(h)

        if targets is not None:
            logits = self.output(h)
            self.last_loss = F.cross_entropy(logits.view(-1, logits.size(-1)), targets.view(-1),
                                             ignore_index=0, reduction='none')
        else:
            logits = self.output(h[:, [-1], :])
            self.last_loss = None

        self.OUT.__setitem__('logits', logits)
        self.OUT.__setitem__('last_loss', self.last_loss)
        return self.OUT

    @torch.inference_mode()
    def generate(self, idx, eos, max_new_tokens, temperature=0.7, top_k=8, stream=True, rp=1., kv_cache=True):
        # rp: repetition_penalty
        index = idx.shape[1]
        init_inference = True
        while idx.shape[1] < max_new_tokens - 1:
            if init_inference or not kv_cache:
                inference_res, init_inference = self(idx, kv_cache=kv_cache), False
            else:
                inference_res = self(idx[:, -1:], kv_cache=kv_cache, current_idx=idx.shape[1] - 1)

            logits = inference_res.logits
            logits = logits[:, -1, :]

            for token in set(idx.tolist()[0]):
                logits[:, token] /= rp

            if temperature == 0.0:
                _, idx_next = torch.topk(logits, k=1, dim=-1)
            else:
                logits = logits / temperature
                if top_k is not None:
                    v, _ = torch.topk(logits, min(top_k, logits.size(-1)))
                    logits[logits < v[:, [-1]]] = -float('Inf')

                probs = F.softmax(logits, dim=-1)
                idx_next = torch.multinomial(probs, num_samples=1, generator=None)

            if idx_next == eos:
                break

            idx = torch.cat((idx, idx_next), dim=1)
            if stream:
                yield idx[:, index:]

        if not stream:
            yield idx[:, index:]

    @torch.inference_mode()
    def eval_answer(self, idx):
        idx_cond = idx if idx.size(1) <= self.params.max_seq_len else idx[:, -self.params.max_seq_len:]
        inference_res = self(idx_cond)
        logits = inference_res.logits
        logits = logits[:, -1, :]
        return logits