marlin.py

from typing import Any, Dict, List, Optional

import torch
from torch.nn.parameter import Parameter

from vllm import _custom_ops as ops
from vllm.model_executor.layers.linear import (LinearMethodBase,
                                               set_weight_attrs)
from vllm.model_executor.layers.quantization.base_config import (
    QuantizationConfig)


class MarlinConfig(QuantizationConfig):
    """Config class for Marlin.

    Reference: https://github.com/IST-DASLab/marlin/tree/master
    """

    def __init__(
        self,
        group_size: int,
    ) -> None:
        # Group size for the quantization.
        self.group_size = group_size
        if self.group_size != 128 and self.group_size != -1:
            raise ValueError(
                "Currently, only group size 128 and -1 (channelwise) "
                "is supported for Marlin, but got group_size of "
                f"{self.group_size}")

        # 4 Bits packed into 32 bit datatype.
        self.pack_factor = 32 // 4

        # Tile size used by marlin kernels.
        self.tile_size = 16

        # Min out_features dim
        self.min_n_threads = 64

        # Min in_features dim
        self.min_k_threads = 128

        # Max parallel problems to solve at once (improves large
        # batch performance)
        self.max_parallel = 16

        # Permutation length used by the marlin kernels.
        self.perm_len = 1024

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

    @classmethod
    def get_name(cls) -> str:
        return "marlin"

    @classmethod
    def get_supported_act_dtypes(cls) -> List[torch.dtype]:
        return [torch.half]

    @classmethod
    # Need to figure it out
    def get_min_capability(cls) -> int:
        return 80

    @classmethod
    def get_config_filenames(cls) -> List[str]:
        return ["quantize_config.json"]

    @classmethod
    def from_config(cls, config: Dict[str, Any]) -> "MarlinConfig":
        group_size = cls.get_from_keys(config, ["group_size"])
        return cls(group_size)

    def get_linear_method(self) -> "MarlinLinearMethod":
        return MarlinLinearMethod(self)

    def get_scaled_act_names(self) -> List[str]:
        return []


class MarlinLinearMethod(LinearMethodBase):
    """Linear method for Marlin.

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

    def __init__(self, quant_config: MarlinConfig):
        self.quant_config = quant_config

    def create_weights(
        self,
        layer: torch.nn.Module,
        input_size_per_partition: int,
        output_size_per_partition: int,
        input_size: int,
        output_size: int,
        params_dtype: torch.dtype,
        **extra_weight_attrs,
    ):
        del output_size  # Unused.

        if params_dtype != torch.float16:
            raise ValueError(
                f"The params dtype must be float16, but got {params_dtype}")

        # Validate output_size_per_partition
        if output_size_per_partition % self.quant_config.min_n_threads != 0:
            raise ValueError(
                f"Weight output_size_per_partition = "
                f"{output_size_per_partition} is not divisible by "
                f"min_n_threads = {self.quant_config.min_n_threads}.")
        if output_size_per_partition % self.quant_config.pack_factor != 0:
            raise ValueError(
                f"Weight output_size_per_partition = "
                f"{output_size_per_partition} is not divisible by "
                f"pack_factor = {self.quant_config.pack_factor}.")

        # Validate input_size_per_partition
        if input_size_per_partition % self.quant_config.min_k_threads != 0:
            raise ValueError(
                f"Weight input_size_per_partition = "
                f"{input_size_per_partition} is not divisible by "
                f"min_k_threads = {self.quant_config.min_k_threads}.")
        if (self.quant_config.group_size != -1 and
                input_size_per_partition % self.quant_config.group_size != 0):
            raise ValueError(f"Weight input_size_per_partition = "
                             f"{input_size_per_partition} is not divisible by "
                             f"group_size = {self.quant_config.group_size}.")

        # Check that we have at least 4 tiles horizontally in the shard
        num_tiles_per_perm = self.quant_config.perm_len // (
            self.quant_config.tile_size**2)
        if output_size_per_partition % num_tiles_per_perm != 0:
            raise ValueError(
                "Each permutation group must reside on the same gpu")

        # Quantized 4Bit weights packed into Int32.
        qweight = Parameter(
            torch.empty(
                input_size_per_partition // self.quant_config.tile_size,
                output_size_per_partition * self.quant_config.tile_size //
                self.quant_config.pack_factor,
                device="cuda",
                dtype=torch.int32,
            ),
            requires_grad=False,
        )
        set_weight_attrs(
            qweight,
            {
                "input_dim": 0,
                "output_dim": 1,
                "packed_dim": 1,
                "pack_factor": self.quant_config.pack_factor,
                "marlin_tile_size": self.quant_config.tile_size,
            },
        )

        # Determine if channelwise or not
        input_groups = (1 if self.quant_config.group_size == -1 else
                        input_size_per_partition //
                        self.quant_config.group_size)

        scales = Parameter(
            torch.empty(
                input_groups,
                output_size_per_partition,
                device="cuda",
                dtype=params_dtype,
            ),
            requires_grad=False,
        )
        set_weight_attrs(
            scales,
            {
                "input_dim": None if input_groups == 1 else 0,
                "output_dim": 1,
            },
        )

        # Allocate workspace (Used for internal locking mechanism)
        max_workspace_size = (
            output_size_per_partition //
            self.quant_config.min_n_threads) * self.quant_config.max_parallel
        workspace = Parameter(torch.zeros(max_workspace_size,
                                          device="cuda",
                                          dtype=torch.int),
                              requires_grad=False)

        layer.register_parameter("B", qweight)
        set_weight_attrs(qweight, extra_weight_attrs)
        layer.register_parameter("s", scales)
        set_weight_attrs(scales, extra_weight_attrs)
        layer.register_parameter("workspace", workspace)
        set_weight_attrs(workspace, extra_weight_attrs)

    def apply_weights(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        bias: Optional[torch.Tensor] = None,
    ) -> torch.Tensor:
        qweight = layer.B
        scales = layer.s
        workspace = layer.workspace

        x_2d = x.view(-1, x.shape[-1])

        size_m = x_2d.shape[0]
        size_k = x_2d.shape[1]
        size_n = scales.shape[1]

        output_2d = ops.marlin_gemm(x_2d, qweight, scales, workspace, size_m,
                                    size_n, size_k)

        output = output_2d.view(x.shape[:-1] + (output_2d.shape[1], ))

        if bias is not None:
            output.add_(bias)  # In-place add

        return output