mlx-lm/mlx_lm/models/phi3.py

# Copyright © 2023-2024 Apple Inc.

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

import mlx.core as mx
import mlx.nn as nn

from .activations import swiglu
from .base import BaseModelArgs, create_attention_mask, scaled_dot_product_attention
from .rope_utils import SuScaledRoPE


@dataclass
class ModelArgs(BaseModelArgs):
    model_type: str
    hidden_size: int
    num_hidden_layers: int
    intermediate_size: int
    num_attention_heads: int
    rms_norm_eps: float
    vocab_size: int
    num_key_value_heads: Optional[int] = None
    rope_theta: float = 10000
    rope_traditional: bool = False
    rope_scaling: Optional[Dict[str, Union[float, List[float]]]] = None
    partial_rotary_factor: float = 1.0
    max_position_embeddings: int = 131072
    original_max_position_embeddings: int = 4096
    tie_word_embeddings: bool = False

    def __post_init__(self):
        if self.num_key_value_heads is None:
            self.num_key_value_heads = self.num_attention_heads

        if self.rope_scaling:
            required_keys = {"long_factor", "type"}
            if not all(key in self.rope_scaling for key in required_keys):
                raise ValueError(f"rope_scaling must contain keys {required_keys}")

            if self.rope_scaling["type"] not in ["longrope", "su", "linear"]:
                print(
                    "[WARNING] rope_scaling 'type' currently only supports 'linear', 'su', and 'longrope'; setting rope scaling to false."
                )
                self.rope_scaling = None


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

        dim = args.hidden_size
        self.n_heads = n_heads = args.num_attention_heads
        assert args.num_key_value_heads is not None
        self.n_kv_heads = n_kv_heads = args.num_key_value_heads
        self.num_hidden_layers = args.num_hidden_layers

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

        op_size = n_heads * head_dim + 2 * (n_kv_heads * head_dim)
        self.qkv_proj = nn.Linear(dim, op_size, bias=False)
        self.o_proj = nn.Linear(n_heads * head_dim, dim, bias=False)

        rope_dim = int(head_dim * args.partial_rotary_factor)
        if args.rope_scaling and args.rope_scaling["type"] in ["longrope", "su"]:
            self.rope = SuScaledRoPE(
                rope_dim,
                base=args.rope_theta,
                max_position_embeddings=args.max_position_embeddings,
                original_max_position_embeddings=args.original_max_position_embeddings,
                short_factor=args.rope_scaling["short_factor"],
                long_factor=args.rope_scaling["long_factor"],
            )
        else:
            rope_scale = 1.0
            if args.rope_scaling and args.rope_scaling["type"] == "linear":
                assert isinstance(args.rope_scaling["factor"], float)
                rope_scale = 1 / args.rope_scaling["factor"]
            self.rope = nn.RoPE(
                rope_dim,
                traditional=args.rope_traditional,
                base=args.rope_theta,
                scale=rope_scale,
            )

    def __call__(
        self,
        x: mx.array,
        mask: Optional[mx.array] = None,
        cache: Optional[Any] = None,
    ) -> mx.array:
        B, L, D = x.shape

        qkv = self.qkv_proj(x)
        query_pos = self.n_heads * self.head_dim
        queries, keys, values = mx.split(
            qkv, [query_pos, query_pos + self.n_kv_heads * self.head_dim], axis=-1
        )

        # Prepare the queries, keys and values for the attention computation
        queries = queries.reshape(B, L, self.n_heads, -1).transpose(0, 2, 1, 3)
        keys = keys.reshape(B, L, self.n_kv_heads, -1).transpose(0, 2, 1, 3)
        values = values.reshape(B, L, self.n_kv_heads, -1).transpose(0, 2, 1, 3)

        if cache is not None:
            queries = self.rope(queries, offset=cache.offset)
            keys = self.rope(keys, offset=cache.offset)
            keys, values = cache.update_and_fetch(keys, values)
        else:
            queries = self.rope(queries)
            keys = self.rope(keys)

        output = scaled_dot_product_attention(
            queries, keys, values, cache=cache, scale=self.scale, mask=mask
        )
        output = output.transpose(0, 2, 1, 3).reshape(B, L, -1)
        return self.o_proj(output)


class MLP(nn.Module):
    def __init__(self, dim, hidden_dim):
        super().__init__()
        self.gate_up_proj = nn.Linear(dim, 2 * hidden_dim, bias=False)
        self.down_proj = nn.Linear(hidden_dim, dim, bias=False)

    def __call__(self, x) -> mx.array:
        x = self.gate_up_proj(x)
        gate, x = mx.split(x, 2, axis=-1)
        return self.down_proj(swiglu(gate, x))


class TransformerBlock(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.num_attention_heads = args.num_attention_heads
        self.hidden_size = args.hidden_size
        self.self_attn = Attention(args)
        self.mlp = MLP(args.hidden_size, args.intermediate_size)
        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.args = args

    def __call__(
        self,
        x: mx.array,
        mask: Optional[mx.array] = None,
        cache: Optional[Any] = None,
    ) -> mx.array:
        r = self.self_attn(self.input_layernorm(x), mask, cache)
        h = x + r
        r = self.mlp(self.post_attention_layernorm(h))
        out = h + r
        return out


class Phi3Model(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.args = args
        self.vocab_size = args.vocab_size
        self.num_hidden_layers = args.num_hidden_layers
        assert self.vocab_size > 0
        self.embed_tokens = nn.Embedding(args.vocab_size, args.hidden_size)
        self.layers = [
            TransformerBlock(args=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)

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

        mask = create_attention_mask(h, cache[0])

        for layer, c in zip(self.layers, cache):
            h = layer(h, mask, c)

        return self.norm(h)


class Model(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.model_type = args.model_type
        self.model = Phi3Model(args)
        if not args.tie_word_embeddings:
            self.lm_head = nn.Linear(args.hidden_size, args.vocab_size, bias=False)
        self.args = args

    def __call__(
        self,
        inputs: mx.array,
        cache=None,
    ):
        out = self.model(inputs, cache)
        if self.args.tie_word_embeddings:
            out = self.model.embed_tokens.as_linear(out)
        else:
            out = self.lm_head(out)
        return out

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