rotary_embedding.py

# coding=utf-8
# Adapted from
# https://github.com/huggingface/transformers/blob/v4.33.2/src/transformers/models/llama/modeling_llama.py
# Copyright 2023 The vLLM team.
# Copyright 2022 EleutherAI and the HuggingFace Inc. team. All rights reserved.
#
# This code is based on EleutherAI's GPT-NeoX library and the GPT-NeoX
# and OPT implementations in this library. It has been modified from its
# original forms to accommodate minor architectural differences compared
# to GPT-NeoX and OPT used by the Meta AI team that trained the model.
#
# 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.
"""Rotary Positional Embeddings."""
import math
from typing import Any, Dict, List, Optional, Tuple, Union

import torch
import torch.nn as nn

from vllm import _custom_ops as ops


def _rotate_neox(x: torch.Tensor) -> torch.Tensor:
    x1 = x[..., :x.shape[-1] // 2]
    x2 = x[..., x.shape[-1] // 2:]
    return torch.cat((-x2, x1), dim=-1)


def _rotate_gptj(x: torch.Tensor) -> torch.Tensor:
    x1 = x[..., ::2]
    x2 = x[..., 1::2]
    x = torch.stack((-x2, x1), dim=-1)
    return x.flatten(-2)


class RotaryEmbedding(nn.Module):
    """Original rotary positional embedding."""

    def __init__(
        self,
        head_size: int,
        rotary_dim: int,
        max_position_embeddings: int,
        base: int,
        is_neox_style: bool,
    ) -> None:
        super().__init__()
        self.head_size = head_size
        self.rotary_dim = rotary_dim
        self.max_position_embeddings = max_position_embeddings
        self.base = base
        self.is_neox_style = is_neox_style

        cache = self._compute_cos_sin_cache()
        cache = cache.to(torch.get_default_dtype())
        self.register_buffer("cos_sin_cache", cache, persistent=False)

    def _compute_inv_freq(self, base: Union[int, float]) -> torch.Tensor:
        """Compute the inverse frequency."""
        # NOTE(woosuk): The HF implementation uses `torch.arange(...).float()`.
        # However, we use `torch.arange(..., dtype=torch.float)` instead to
        # avoid numerical issues with large base values (e.g., 10000000).
        # This may cause a slight numerical difference between the HF
        # implementation and ours.
        # NOTE(woosuk): To exactly match the HF implementation, we need to
        # use CPU to compute the cache and then move it to GPU. However, we
        # create the cache on GPU for faster initialization. This may cause
        # a slight numerical difference between the HF implementation and ours.
        inv_freq = 1.0 / (base**(torch.arange(
            0, self.rotary_dim, 2, dtype=torch.float) / self.rotary_dim))
        return inv_freq

    def _compute_cos_sin_cache(self) -> torch.Tensor:
        """Compute the cos and sin cache."""
        inv_freq = self._compute_inv_freq(self.base)
        t = torch.arange(self.max_position_embeddings, dtype=torch.float)

        freqs = torch.einsum("i,j -> ij", t, inv_freq)
        cos = freqs.cos()
        sin = freqs.sin()
        cache = torch.cat((cos, sin), dim=-1)
        return cache

    def _forward(
        self,
        positions: torch.Tensor,
        query: torch.Tensor,
        key: torch.Tensor,
        offsets: Optional[torch.Tensor] = None,
    ) -> Tuple[torch.Tensor, torch.Tensor]:
        """PyTorch-native implementation equivalent to forward()."""
        query = query.view(*query.shape[:-1], -1, self.head_size)
        key = key.view(*key.shape[:-1], -1, self.head_size)

        query_rot = query[..., :self.rotary_dim]
        key_rot = key[..., :self.rotary_dim]
        if self.rotary_dim < self.head_size:
            query_pass = query[..., self.rotary_dim:]
            key_pass = key[..., self.rotary_dim:]

        self.cos_sin_cache: torch.Tensor = self.cos_sin_cache.to(
            positions.device)
        cos_sin = self.cos_sin_cache[torch.add(positions, offsets)
                                     if offsets is not None else positions]
        cos, sin = cos_sin.chunk(2, dim=-1)
        if self.is_neox_style:
            # NOTE(woosuk): Here we assume that the positions tensor has the
            # shape [batch_size, seq_len].
            cos = cos.repeat(1, 1, 2).unsqueeze(-2)
            sin = sin.repeat(1, 1, 2).unsqueeze(-2)
        else:
            cos = cos.repeat_interleave(2, dim=-1).unsqueeze(-2)
            sin = sin.repeat_interleave(2, dim=-1).unsqueeze(-2)

        rotate_fn = _rotate_neox if self.is_neox_style else _rotate_gptj
        query_rot = query_rot * cos + rotate_fn(query_rot) * sin
        key_rot = key_rot * cos + rotate_fn(key_rot) * sin

        if self.rotary_dim < self.head_size:
            query = torch.cat((query_rot, query_pass), dim=-1)
            key = torch.cat((key_rot, key_pass), dim=-1)
        else:
            query = query_rot
            key = key_rot
        query = query.flatten(-2)
        key = key.flatten(-2)
        return query, key

    def forward(
        self,
        positions: torch.Tensor,
        query: torch.Tensor,
        key: torch.Tensor,
        offsets: Optional[torch.Tensor] = None,
    ) -> Tuple[torch.Tensor, torch.Tensor]:
        self.cos_sin_cache = self.cos_sin_cache.to(positions.device)
        # ops.rotary_embedding()/batched_rotary_embedding()
        # are in-place operations that update the query and key tensors.
        if offsets is not None:
            ops.batched_rotary_embedding(positions, query, key, self.head_size,
                                         self.cos_sin_cache,
                                         self.is_neox_style, self.rotary_dim,
                                         offsets)
        else:
            ops.rotary_embedding(positions, query, key, self.head_size,
                                 self.cos_sin_cache, self.is_neox_style)
        return query, key


class LinearScalingRotaryEmbedding(RotaryEmbedding):
    """RotaryEmbedding extended with linear scaling.

    Credits to the Reddit user /u/kaiokendev
    """

    def __init__(
        self,
        head_size: int,
        rotary_dim: int,
        max_position_embeddings: int,
        base: int,
        is_neox_style: bool,
        scaling_factors: Union[List[float], float],
    ) -> None:
        if isinstance(scaling_factors, float):
            scaling_factors = [scaling_factors]
        self.scaling_factors = scaling_factors
        super().__init__(head_size, rotary_dim, max_position_embeddings, base,
                         is_neox_style)

    def _compute_cos_sin_cache(self) -> torch.Tensor:
        inv_freq = self._compute_inv_freq(self.base)
        cache_list = []
        for scaling_factor in self.scaling_factors:
            # NOTE(woosuk): self.max_position_embeddings is the original
            # maximum length before applying the rope scaling.
            # Thus, the maximum length after applying the rope scaling is
            # self.max_position_embeddings * self.scaling_factor.
            max_len = self.max_position_embeddings * scaling_factor
            t = torch.arange(max_len, dtype=torch.float)
            t = t / scaling_factor

            freqs = torch.einsum("i,j -> ij", t, inv_freq)
            cos = freqs.cos()
            sin = freqs.sin()
            cache = torch.cat((cos, sin), dim=-1)
            cache_list.append(cache)
        return torch.cat(cache_list, dim=0)


class DynamicNTKScalingRotaryEmbedding(RotaryEmbedding):
    """RotaryEmbedding extended with Dynamic NTK scaling.

    Credits to the Reddit users /u/bloc97 and /u/emozilla
    """

    def __init__(
        self,
        head_size: int,
        rotary_dim: int,
        max_position_embeddings: int,
        base: int,
        is_neox_style: bool,
        scaling_factor: float,
    ) -> None:
        self.scaling_factor = scaling_factor
        super().__init__(head_size, rotary_dim, max_position_embeddings, base,
                         is_neox_style)

    def _compute_cos_sin_cache(self) -> torch.Tensor:
        # NOTE(woosuk): self.max_position_embeddings is the original
        # maximum length before applying the rope scaling.
        # Thus, the maximum length after applying the rope scaling is
        # self.max_position_embeddings * self.scaling_factor.
        max_len = self.max_position_embeddings * self.scaling_factor
        base = self.base * (
            (self.scaling_factor * max_len / self.max_position_embeddings) -
            (self.scaling_factor - 1))**(self.rotary_dim /
                                         (self.rotary_dim - 2))
        inv_freq = self._compute_inv_freq(base)
        t = torch.arange(max_len, dtype=torch.float)

        freqs = torch.einsum("i,j -> ij", t, inv_freq)
        cos = freqs.cos()
        sin = freqs.sin()
        cache = torch.cat((cos, sin), dim=-1)
        return cache


# Inverse dim formula to find dim based on number of rotations
def _yarn_find_correction_dim(num_rotations: int,
                              dim: int,
                              base: float = 10000,
                              max_position_embeddings: int = 2048) -> float:
    return (dim * math.log(max_position_embeddings /
                           (num_rotations * 2 * math.pi))) / (2 *
                                                              math.log(base))


# Find dim range bounds based on rotations
def _yarn_find_correction_range(
        low_rot: int,
        high_rot: int,
        dim: int,
        base: float = 10000,
        max_position_embeddings: int = 2048) -> Tuple[int, int]:
    low = math.floor(
        _yarn_find_correction_dim(low_rot, dim, base, max_position_embeddings))
    high = math.ceil(
        _yarn_find_correction_dim(high_rot, dim, base,
                                  max_position_embeddings))
    return max(low, 0), min(high, dim - 1)  # Clamp values just in case


def _yarn_linear_ramp_mask(low: float, high: float, dim: int,
                           dtype: torch.dtype) -> torch.Tensor:
    if low == high:
        high += 0.001  # Prevent singularity

    linear_func = (torch.arange(dim, dtype=dtype) - low) / (high - low)
    ramp_func = torch.clamp(linear_func, 0, 1)
    return ramp_func


def _yarn_get_mscale(scale: float = 1) -> float:
    if scale <= 1:
        return 1.0
    return 0.1 * math.log(scale) + 1.0


class YaRNScalingRotaryEmbedding(RotaryEmbedding):
    """RotaryEmbedding extended with YaRN method.

    Credits to Peng et al. github.com/jquesnelle/yarn
    """

    def __init__(
        self,
        head_size: int,
        rotary_dim: int,
        max_position_embeddings: int,
        base: int,
        is_neox_style: bool,
        scaling_factor: float,
        *,
        extrapolation_factor: float = 1,
        attn_factor: float = 1,
        beta_fast: int = 32,
        beta_slow: int = 1,
    ) -> None:
        self.scaling_factor = scaling_factor
        self.extrapolation_factor = extrapolation_factor
        self.attn_factor = attn_factor
        self.beta_fast = beta_fast
        self.beta_slow = beta_slow
        # Get n-d magnitude scaling corrected for interpolation
        self.mscale = float(
            _yarn_get_mscale(self.scaling_factor) * attn_factor)
        super().__init__(head_size, rotary_dim, max_position_embeddings, base,
                         is_neox_style)

    def _compute_inv_freq(self, scaling_factor: float) -> torch.Tensor:
        pos_freqs = self.base**(
            torch.arange(0, self.rotary_dim, 2, dtype=torch.float) /
            self.rotary_dim)
        inv_freq_extrapolation = 1.0 / pos_freqs
        inv_freq_interpolation = 1.0 / (scaling_factor * pos_freqs)

        low, high = _yarn_find_correction_range(self.beta_fast, self.beta_slow,
                                                self.rotary_dim, self.base,
                                                self.max_position_embeddings)
        # Get n-d rotational scaling corrected for extrapolation
        inv_freq_mask = (1 - _yarn_linear_ramp_mask(
            low, high, self.rotary_dim // 2,
            dtype=torch.float)) * self.extrapolation_factor
        inv_freq = inv_freq_interpolation * (
            1 - inv_freq_mask) + inv_freq_extrapolation * inv_freq_mask
        return inv_freq

    def _compute_cos_sin_cache(self) -> torch.Tensor:
        inv_freq = self._compute_inv_freq(self.scaling_factor)
        t = torch.arange(self.max_position_embeddings * self.scaling_factor,
                         dtype=torch.float32)
        freqs = torch.einsum("i,j -> ij", t, inv_freq)
        cos = (freqs.cos() * self.mscale)
        sin = (freqs.sin() * self.mscale)
        cache = torch.cat((cos, sin), dim=-1)
        return cache


class Phi3SuScaledRotaryEmbedding(nn.Module):
    """Phi3 family of models scaled rotary embedding.

    Based on the original RotaryEmbedding implementation.
    """

    def __init__(
        self,
        head_size: int,
        rotary_dim: int,
        max_position_embeddings: int,
        original_max_position_embeddings: int,
        base: int,
        is_neox_style: bool,
        short_factor: List[float],
        long_factor: List[float],
        short_mscale: float = 1.1,
        long_mscale: float = 1.225,
    ):
        super().__init__()

        if rotary_dim != head_size:
            raise ValueError(
                f"`Phi3SuScaledRotaryEmbedding` does not support rotary_dim != \
                    head_size ({rotary_dim}!={head_size}).")
        if is_neox_style is False:
            raise ValueError(
                "`Phi3SuScaledRotaryEmbedding` only supports neox_style.")

        self.head_size = head_size
        self.max_position_embeddings = max_position_embeddings
        self.original_max_position_embeddings = original_max_position_embeddings
        self.base = base
        self.short_factor = short_factor
        self.long_factor = long_factor
        self.short_mscale = short_mscale
        self.long_mscale = long_mscale

        short_cache = self._compute_cos_sin_cache(
            original_max_position_embeddings, short_factor, short_mscale)
        short_cache = short_cache.to(torch.get_default_dtype())
        self.register_buffer("short_cos_sin_cache",
                             short_cache,
                             persistent=False)

        long_cache = self._compute_cos_sin_cache(max_position_embeddings,
                                                 long_factor, long_mscale)
        long_cache = long_cache.to(torch.get_default_dtype())
        self.register_buffer("long_cos_sin_cache",
                             long_cache,
                             persistent=False)

        long_short_cache = torch.cat(
            [self.short_cos_sin_cache, self.long_cos_sin_cache], dim=0)
        self.register_buffer("long_short_cos_sin_cache",
                             long_short_cache,
                             persistent=False)

    def _compute_inv_freq(self, rescale_factors: List[float]) -> torch.Tensor:
        rescale_factors = torch.tensor(rescale_factors, dtype=torch.float32)
        inv_freq = 1.0 / (rescale_factors * (self.base**(torch.arange(
            0, self.head_size, 2, dtype=torch.float) / self.head_size)))
        return inv_freq

    def _compute_cos_sin_cache(
        self,
        max_position_embeddings: int,
        rescale_factors: List[float],
        mscale: float,
    ) -> torch.Tensor:
        inv_freq = self._compute_inv_freq(rescale_factors)
        t = torch.arange(max_position_embeddings, dtype=torch.float)
        freqs = torch.einsum("i,j -> ij", t, inv_freq)
        cos = freqs.cos() * mscale
        sin = freqs.sin() * mscale
        cache = torch.cat((cos, sin), dim=-1)
        return cache

    def forward(
        self,
        positions: torch.Tensor,
        query: torch.Tensor,
        key: torch.Tensor,
        offsets: Optional[torch.Tensor] = None,
    ) -> Tuple[torch.Tensor, torch.Tensor]:
        query = query.view(*query.shape[:-1], -1, self.head_size)
        key = key.view(*key.shape[:-1], -1, self.head_size)

        k = self.original_max_position_embeddings
        long_prompt_offset = (torch.any(positions > k).float() *
                              torch.full_like(positions, k)).long()
        idx = (torch.add(positions, long_prompt_offset)
               if long_prompt_offset is not None else positions)
        self.long_short_cos_sin_cache: torch.Tensor = (
            self.long_short_cos_sin_cache.to(idx.device))
        idx = torch.add(idx, offsets) if offsets is not None else idx
        cos_sin = torch.index_select(self.long_short_cos_sin_cache, 0, idx)

        cos, sin = cos_sin.chunk(2, dim=-1)
        cos = cos.repeat(1, 2).unsqueeze(-2)
        sin = sin.repeat(1, 2).unsqueeze(-2)

        query = query * cos + _rotate_neox(query) * sin
        key = key * cos + _rotate_neox(key) * sin

        return query.flatten(-2), key.flatten(-2)


_ROPE_DICT: Dict[Tuple, RotaryEmbedding] = {}


def get_rope(
    head_size: int,
    rotary_dim: int,
    max_position: int,
    base: int,
    is_neox_style: bool = True,
    rope_scaling: Optional[Dict[str, Any]] = None,
) -> RotaryEmbedding:
    if rope_scaling is not None:
        # Transforms every value that is a list into a tuple for caching calls
        rope_scaling_tuple = {
            k: tuple(v) if isinstance(v, list) else v
            for k, v in rope_scaling.items()
        }
        rope_scaling_args = tuple(rope_scaling_tuple.items())
    else:
        rope_scaling_args = None
    key = (head_size, rotary_dim, max_position, base, is_neox_style,
           rope_scaling_args)
    if key in _ROPE_DICT:
        return _ROPE_DICT[key]
    if rope_scaling is None:
        rotary_emb = RotaryEmbedding(head_size, rotary_dim, max_position, base,
                                     is_neox_style)
    else:
        scaling_type = rope_scaling["type"]
        if scaling_type != "su":
            scaling_factor = rope_scaling["factor"]
        if scaling_type == "linear":
            rotary_emb = LinearScalingRotaryEmbedding(head_size, rotary_dim,
                                                      max_position, base,
                                                      is_neox_style,
                                                      scaling_factor)
        elif scaling_type == "dynamic":
            rotary_emb = DynamicNTKScalingRotaryEmbedding(
                head_size, rotary_dim, max_position, base, is_neox_style,
                scaling_factor)
        elif scaling_type == "yarn":
            original_max_position = rope_scaling[
                "original_max_position_embeddings"]
            extra_kwargs = {
                k: v
                for k, v in rope_scaling.items()
                if k in ("extrapolation_factor", "attn_factor", "beta_fast",
                         "beta_slow")
            }
            rotary_emb = YaRNScalingRotaryEmbedding(head_size, rotary_dim,
                                                    original_max_position,
                                                    base, is_neox_style,
                                                    scaling_factor,
                                                    **extra_kwargs)
        elif scaling_type == "su":
            short_factor = rope_scaling["short_factor"]
            long_factor = rope_scaling["long_factor"]
            original_max_position = rope_scaling[
                "original_max_position_embeddings"]
            extra_kwargs = {
                k: v
                for k, v in rope_scaling.items()
                if k in ("short_mscale", "long_mscale")
            }
            rotary_emb = Phi3SuScaledRotaryEmbedding(
                head_size, rotary_dim, max_position, original_max_position,
                base, is_neox_style, short_factor, long_factor, **extra_kwargs)
        else:
            raise ValueError(f"Unknown RoPE scaling type {scaling_type}")
    _ROPE_DICT[key] = rotary_emb
    return rotary_emb