bitsandbytes.py

from typing import Any, Dict, List, Optional

import torch
from torch.nn.parameter import Parameter

from vllm.model_executor.layers.linear import (LinearBase, LinearMethodBase,
                                               set_weight_attrs)
from vllm.model_executor.layers.quantization.base_config import (
    QuantizationConfig)


class BitsAndBytesConfig(QuantizationConfig):
    """Config class for BitsAndBytes Quantization.

    Reference: https://arxiv.org/abs/2305.14314
    """

    def __init__(
        self,
        adapter_name_or_path: str,
        target_modules: List[str],
    ) -> None:

        self.adapter_name_or_path = adapter_name_or_path
        self.target_modules = target_modules

    def __repr__(self) -> str:
        return (
            f"BitsAndBytesConfig(adapter_name_or_path={self.adapter_name_or_path}"
        )

    @classmethod
    def get_name(self) -> str:
        return "bitsandbytes"

    @classmethod
    def get_supported_act_dtypes(self) -> List[torch.dtype]:
        return [torch.float32, torch.float16, torch.bfloat16]

    @classmethod
    def get_min_capability(cls) -> int:
        return 70

    @staticmethod
    def get_config_filenames() -> List[str]:
        return [
            "adapter_config.json",
        ]

    @classmethod
    def from_config(cls, config: Dict[str, Any]) -> "BitsAndBytesConfig":
        adapter_name = cls.get_from_keys(config, ["adapter_name_or_path"])
        default_target_modules = [
            "gate_proj", "down_proj", "up_proj", "q_proj", "k_proj", "v_proj",
            "o_proj"
        ]
        if adapter_name == "":
            target_modules = default_target_modules
        else:
            target_modules = cls.get_from_keys(config, ["target_modules"])
        return cls(adapter_name, target_modules)

    def get_quant_method(
            self,
            layer: torch.nn.Module) -> Optional["BitsAndBytesLinearMethod"]:
        if isinstance(layer, LinearBase):
            return BitsAndBytesLinearMethod(self)
        return None

    def get_scaled_act_names(self) -> List[str]:
        return ["gelu", "gelu_fast", "gelu_new", "gelu_pytorch_tanh"]


class BitsAndBytesLinearMethod(LinearMethodBase):
    """Linear method for BitsAndBytes.

    Args:
       quant_config: The BitsAndBytes quantization config.
    """

    def __init__(self, quant_config: BitsAndBytesConfig):
        try:
            import bitsandbytes
            if bitsandbytes.__version__ < "0.42.0":
                raise ImportError("bitsandbytes version is wrong. Please "
                                  "install bitsandbytes>=0.42.0.")
        except ImportError as err:
            raise ImportError("Please install bitsandbytes>=0.42.0 via "
                              "`pip install bitsandbytes>=0.42.0` to use "
                              "bitsandbytes quantizer.") from err

        self.quant_config = quant_config

    def create_weights(self, layer: torch.nn.Module,
                       input_size_per_partition: int,
                       output_partition_sizes: List[int], input_size: int,
                       output_size: int, params_dtype: torch.dtype,
                       **extra_weight_attrs):
        quant_ratio = 0
        if params_dtype.is_floating_point:
            quant_ratio = torch.finfo(params_dtype).bits // torch.iinfo(
                torch.uint8).bits
        else:
            quant_ratio = torch.iinfo(params_dtype).bits // torch.iinfo(
                torch.uint8).bits

        if input_size_per_partition * sum(
                output_partition_sizes) % quant_ratio != 0:
            raise ValueError(
                "The input size is not aligned with the quantized "
                "weight shape. ")
        qweight = Parameter(
            torch.empty(
                input_size_per_partition * sum(output_partition_sizes) //
                quant_ratio,
                1,
                dtype=torch.uint8,
            ),
            requires_grad=False,
        )

        set_weight_attrs(
            qweight,
            {
                "input_dim": 0,
                # In bitsandbytes, a tensor of shape [n,m] is quantized to
                #[n*m/pack_ratio, 1],so the output_dim is 0
                "output_dim": 0,
                "pack_factor": quant_ratio,
                "use_bitsandbytes": True,
            })
        layer.register_parameter("qweight", qweight)
        set_weight_attrs(qweight, extra_weight_attrs)

    def apply(self,
              layer: torch.nn.Module,
              x: torch.Tensor,
              bias: Optional[torch.Tensor] = None) -> torch.Tensor:

        # only load the bitsandbytes module when needed
        from bitsandbytes import matmul_4bit

        original_type = x.dtype
        bf_x = x.to(torch.bfloat16)

        qweight = layer.qweight
        quant_states = qweight.bnb_quant_state
        offsets = qweight.bnb_shard_offsets

        out_dim_0 = x.shape[0]
        out_dim_1 = sum(
            [quant_state[1].shape[0] for quant_state in quant_states.items()])
        out = torch.empty(out_dim_0,
                          out_dim_1,
                          dtype=torch.bfloat16,
                          device=x.device)

        current_index = 0
        for i in range(len(quant_states)):
            output_size = quant_states[i].shape[0]
            # It is more efficient to use out kwarg like
            # matmul_4bit(..., out = ...).  Infeasible now due to the bug
            # https://github.com/TimDettmers/bitsandbytes/issues/1235.
            # Need to change  after the bug is fixed.
            out[:, current_index:current_index + output_size] = matmul_4bit(
                bf_x, qweight[offsets[i]:offsets[i + 1]].t(), quant_states[i])

            current_index += output_size

        out = out.to(original_type)

        if bias is not None:
            out += bias

        return out