mlx-examples/llms/mlx_lm/models/minicpm.py

from dataclasses import dataclass
from typing import Dict, Optional, Tuple, Union

import mlx.core as mx
import mlx.nn as nn
import numpy as np

from .base import BaseModelArgs


@dataclass
class ModelArgs(BaseModelArgs):
    model_type: str
    hidden_size: int
    dim_model_base: int
    num_hidden_layers: int
    intermediate_size: int
    num_attention_heads: int
    rms_norm_eps: float
    vocab_size: int
    num_key_value_heads: int
    max_position_embeddings: int
    scale_depth: float
    scale_emb: float
    rope_theta: float = 1000000.0
    rope_traditional: bool = False
    rope_scaling: Optional[Dict[str, Union[str, float]]] = None
    tie_word_embeddings: bool = False


class MLP(nn.Module):
    def __init__(self, args):
        super().__init__()
        self.gate_proj = nn.Linear(args.hidden_size, args.intermediate_size, bias=False)
        self.up_proj = nn.Linear(args.hidden_size, args.intermediate_size, bias=False)
        self.down_proj = nn.Linear(args.intermediate_size, args.hidden_size, bias=False)

    def __call__(self, x):
        return self.down_proj(nn.silu(self.gate_proj(x)) * self.up_proj(x))


class Attention(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.args = args

        self.hidden_size = args.hidden_size
        self.num_heads = n_heads = args.num_attention_heads
        self.rope_theta = args.rope_theta
        self.max_position_embeddings = args.max_position_embeddings

        self.head_dim = head_dim = args.hidden_size // n_heads
        self.scale = head_dim**-0.5

        self.num_key_value_heads = args.num_key_value_heads
        self.num_key_value_groups = self.num_heads // self.num_key_value_heads

        self.q_proj = nn.Linear(
            self.hidden_size, self.num_heads * self.head_dim, bias=False
        )
        self.k_proj = nn.Linear(
            self.hidden_size, self.num_key_value_heads * self.head_dim, bias=False
        )
        self.v_proj = nn.Linear(
            self.hidden_size, self.num_key_value_heads * self.head_dim, bias=False
        )
        self.o_proj = nn.Linear(
            self.num_heads * self.head_dim, self.hidden_size, bias=False
        )

        rope_scale = (
            1 / args.rope_scaling["factor"]
            if args.rope_scaling is not None and args.rope_scaling["type"] == "linear"
            else 1
        )

        self.rope = nn.RoPE(
            dims=self.head_dim,
            traditional=args.rope_traditional,
            base=self.rope_theta,
            scale=rope_scale,
        )

    def __call__(
        self,
        x: mx.array,
        mask: Optional[mx.array] = None,
        cache: Optional[Tuple[mx.array, mx.array]] = None,
    ):
        B, L, _ = x.shape

        queries, keys, values = self.q_proj(x), self.k_proj(x), self.v_proj(x)

        queries = queries.reshape(B, L, self.num_heads, -1).transpose(0, 2, 1, 3)
        keys = keys.reshape(B, L, self.num_key_value_heads, -1).transpose(0, 2, 1, 3)
        values = values.reshape(B, L, self.num_key_value_heads, -1).transpose(
            0, 2, 1, 3
        )

        if cache is not None:
            key_cache, value_cache = cache
            queries = self.rope(queries, offset=key_cache.shape[2])
            keys = self.rope(keys, offset=key_cache.shape[2])
            keys = mx.concatenate([key_cache, keys], axis=2)
            values = mx.concatenate([value_cache, values], axis=2)
        else:
            queries = self.rope(queries)
            keys = self.rope(keys)

        attn_output = mx.fast.scaled_dot_product_attention(
            queries, keys, values, scale=self.scale, mask=mask
        )

        attn_output = attn_output.transpose(0, 2, 1, 3).reshape(B, L, -1)

        return self.o_proj(attn_output), (keys, values)


class DecoderLayer(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.args = args
        self.hidden_size = args.hidden_size
        self.num_hidden_layers = args.num_hidden_layers

        self.self_attn = Attention(args)
        self.mlp = MLP(args)
        self.input_layernorm = nn.RMSNorm(args.hidden_size, eps=args.rms_norm_eps)
        self.post_attention_layernorm = nn.RMSNorm(
            args.hidden_size, eps=args.rms_norm_eps
        )

        self.scale_depth = args.scale_depth
        self.num_hidden_layers = args.num_hidden_layers

    def __call__(
        self,
        x: mx.array,
        mask: Optional[mx.array] = None,
        cache: Optional[Tuple[mx.array, mx.array]] = None,
    ) -> mx.array:
        r, cache = self.self_attn(self.input_layernorm(x), mask, cache)
        h = x + r * (self.scale_depth / np.sqrt(self.num_hidden_layers))
        r = self.mlp(self.post_attention_layernorm(h))
        out = h + r * (self.scale_depth / np.sqrt(self.num_hidden_layers))
        return out, cache


class MiniCPMModel(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.args = args
        self.vocab_size = args.vocab_size
        assert self.vocab_size > 0

        self.embed_tokens = nn.Embedding(args.vocab_size, args.hidden_size)
        self.layers = [DecoderLayer(args) for _ in range(args.num_hidden_layers)]
        self.norm = nn.RMSNorm(args.hidden_size, eps=args.rms_norm_eps)

    def __call__(
        self,
        inputs: mx.array,
        cache=None,
    ):
        h = self.embed_tokens(inputs) * self.args.scale_emb

        mask = None
        if h.shape[1] > 1:
            mask = nn.MultiHeadAttention.create_additive_causal_mask(h.shape[1])
            mask = mask.astype(h.dtype)

        if cache is None:
            cache = [None] * len(self.layers)

        for e, layer in enumerate(self.layers):
            h, cache[e] = layer(h, mask, cache[e])

        return self.norm(h), cache


class Model(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.args = args
        self.model_type = args.model_type
        self.model = MiniCPMModel(args)

        if not self.args.tie_word_embeddings:
            self.lm_head = nn.Linear(args.hidden_size, args.vocab_size, bias=False)

    def __call__(
        self,
        inputs: mx.array,
        cache=None,
    ):
        out, cache = self.model(inputs, cache)

        if not self.args.tie_word_embeddings:
            out = self.lm_head(out / (self.args.hidden_size / self.args.dim_model_base))
        else:
            out = out @ self.model.embed_tokens.weight.T

        return out, cache

    def sanitize(self, weights):
        if "lm_head.weight" not in weights:
            weights["lm_head.weight"] = weights["model.embed_tokens.weight"]
        return weights

    @property
    def layers(self):
        return self.model.layers