petit.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
# Adapted from https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/layers/quantization/modelopt.py

from typing import Any, Optional

import regex as re
import torch
from torch.nn.parameter import Parameter

from vllm.attention.layer import Attention
from vllm.logger import init_logger
from vllm.model_executor.layers.linear import (
    LinearBase,
    LinearMethodBase,
    UnquantizedLinearMethod,
)
from vllm.model_executor.layers.quantization import QuantizationMethods
from vllm.model_executor.layers.quantization.base_config import (
    QuantizationConfig,
    QuantizeMethodBase,
)
from vllm.model_executor.layers.quantization.kv_cache import BaseKVCacheMethod
from vllm.model_executor.layers.quantization.utils.petit_utils import (
    apply_petit_nvfp4_linear,
    prepare_nvfp4_layer_for_petit,
    verify_petit_nvfp4_supported,
)
from vllm.model_executor.layers.quantization.utils.quant_utils import is_layer_skipped
from vllm.model_executor.parameter import ModelWeightParameter, PerTensorScaleParameter
from vllm.platforms import current_platform

# Initialize logger for the module
logger = init_logger(__name__)


# Configuration class to support the NVFP4 quantized model
# generated by the ModelOpt quantization tool
class PetitNvFp4Config(QuantizationConfig):
    """Config class for Petit FP4."""

    def __init__(
        self,
        is_checkpoint_nvfp4_serialized: bool = False,
        kv_cache_quant_algo: str | None = None,
        group_size: int | None = None,
        exclude_modules: list[str] | None = None,
    ) -> None:
        self._check_hardware_support()
        self.is_checkpoint_nvfp4_serialized = is_checkpoint_nvfp4_serialized
        if is_checkpoint_nvfp4_serialized:
            logger.warning(
                "Detected nvfp4 checkpoint. Please note that the "
                "format is experimental and subject to change."
            )
        self.group_size = group_size
        self.kv_cache_quant_algo = kv_cache_quant_algo
        self.exclude_modules = exclude_modules

    def _check_hardware_support(self) -> None:
        """
        Verifies that the current hardware is supported by the Petit backend.
        This backend is specifically designed for AMD GPUs and is not
        supported on the CUDA platform.
        """
        # This check ensures the code is NOT running on an NVIDIA GPU.
        if current_platform.is_cuda():
            raise ValueError(
                "The 'petit' quantization backend is designed for AMD GPUs "
                "and is not supported on the CUDA platform. For NVIDIA GPUs, "
                "please use a different quantization method such as FP8, AWQ, "
                "or GPTQ."
            )

    @classmethod
    def get_name(cls) -> QuantizationMethods:
        return "petit_nvfp4"

    @classmethod
    def get_supported_act_dtypes(cls) -> list[torch.dtype]:
        return [torch.bfloat16, torch.half]

    @classmethod
    def get_min_capability(cls) -> int:
        # Petit supports the gfx90a and gfx942 GPUs
        return 90

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

    @classmethod
    def from_config(cls, config: dict[str, Any]) -> "PetitNvFp4Config":
        qc = cls.get_from_keys(config, ["quantization"])

        quant_method_raw = qc.get("quant_algo")
        if not isinstance(quant_method_raw, str) or not quant_method_raw:
            raise ValueError("Missing or invalid 'quant_algo' in quantization config.")
        quant_method = quant_method_raw.upper()

        group_size_raw = qc.get("group_size")
        if not isinstance(group_size_raw, int):
            raise ValueError(
                "Missing or invalid 'group_size' (int) in hf_quant_config.json."
            )
        group_size = group_size_raw

        verify_petit_nvfp4_supported(quant_method, group_size)

        kv_cache_quant_algo_raw = qc.get("kv_cache_quant_algo") or "auto"
        if not isinstance(kv_cache_quant_algo_raw, str):
            raise ValueError("'kv_cache_quant_algo' must be a string if provided.")
        kv_cache_quant_algo = kv_cache_quant_algo_raw

        exclude_raw = qc.get("exclude_modules", [])
        if exclude_raw is None:
            exclude_modules: list[str] = []
        elif isinstance(exclude_raw, list) and all(
            isinstance(x, str) for x in exclude_raw
        ):
            exclude_modules = exclude_raw
        else:
            raise ValueError("'exclude_modules' must be a list[str] (or omitted).")

        is_checkpoint_nvfp4_serialized = "NVFP4" in quant_method

        return cls(
            is_checkpoint_nvfp4_serialized=is_checkpoint_nvfp4_serialized,
            kv_cache_quant_algo=kv_cache_quant_algo,
            group_size=group_size,
            exclude_modules=exclude_modules,
        )

    @classmethod
    def override_quantization_method(
        cls, hf_quant_cfg, user_quant
    ) -> QuantizationMethods | None:
        if not current_platform.is_rocm():
            return None

        qc = hf_quant_cfg.get("quantization", hf_quant_cfg)
        algo = (qc.get("quant_algo") or qc.get("quant_method") or "").upper()
        if algo in ("NVFP4", "MODELOPT_FP4", "MODELOPT"):
            return cls.get_name()  # "petit_nvfp4"
        return None

    @classmethod
    def is_petit_nvfp4_compatible(cls, quant_config: dict[str, Any]) -> bool:
        qc = quant_config.get("quantization", quant_config)
        algo = (qc.get("quant_algo") or qc.get("quant_method") or "").upper()
        return algo == "NVFP4"

    def is_layer_excluded(self, prefix: str, exclude_modules: list[str]) -> bool:
        for pattern in exclude_modules:
            regex_str = pattern.replace(".", r"\.").replace("*", r".*")
            if re.fullmatch(regex_str, prefix):
                return True
        return False

    def get_quant_method(
        self, layer: torch.nn.Module, prefix: str
    ) -> Optional["QuantizeMethodBase"]:
        exclude = self.require_exclude_modules()

        if isinstance(layer, LinearBase):
            if is_layer_skipped(prefix, exclude) or self.is_layer_excluded(
                prefix, exclude
            ):
                return UnquantizedLinearMethod()
            return PetitNvFp4LinearMethod(self)
        elif isinstance(layer, Attention):
            return PetitFp8KVCacheMethod(self)
        return None

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

    def require_group_size(self) -> int:
        if self.group_size is None:
            logger.warning("group_size not set; defaulting to 16 for NVFP4.")
            return 16
        return self.group_size

    def require_kv_cache_quant_algo(self) -> str:
        return self.kv_cache_quant_algo or "auto"

    def require_exclude_modules(self) -> list[str]:
        return list(self.exclude_modules or [])


class PetitFp8KVCacheMethod(BaseKVCacheMethod):
    """
    Supports loading kv-cache scaling factors from FP8 checkpoints.
    """

    def __init__(self, quant_config: PetitNvFp4Config):
        super().__init__(quant_config)


class PetitNvFp4LinearMethod(LinearMethodBase):
    """Linear method for NVFP4.
    Supports loading NVFP4 checkpoints with the following structure:

    |Tensor Name           | datatype      |  shape      |
    |----------------------------------------------------|
    |input_scale           | torch.float32 | scalar      |
    |weight                | NVFP4(SE2M1)  | [1, X, y/2] |
    |weight_scale          | FP8-E4M3      | [X, Y]      |
    |weight_scale_2        | torch.float32 | scalar      |

    The weights are quantized per block of 16 elements.
    Args: quant_config: The ModelOpt quantization config.
    """

    def __init__(self, quant_config: PetitNvFp4Config):
        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,
    ):
        del input_size, output_size
        if not self.quant_config.is_checkpoint_nvfp4_serialized:
            raise ValueError(
                "NVFP4 quantization was selected, "
                " dynamic quantization is not supported."
            )

        output_size_per_partition = sum(output_partition_sizes)
        weight_loader = extra_weight_attrs.get("weight_loader")

        layer.logical_widths = output_partition_sizes

        layer.input_size_per_partition = input_size_per_partition
        layer.output_size_per_partition = output_size_per_partition
        if input_size_per_partition % 16 != 0:
            raise ValueError(
                "Unsupported model when in features size is not multiple of 16"
            )

        weight_dtype = (
            torch.float8_e4m3fn
            if self.quant_config.is_checkpoint_nvfp4_serialized
            else params_dtype
        )

        weight = ModelWeightParameter(
            data=torch.empty(
                # 2 fp4 data is packed in one uint8 in the input dimension
                output_size_per_partition,
                input_size_per_partition // 2,
                dtype=torch.uint8,
            ),
            input_dim=1,
            output_dim=0,
            weight_loader=weight_loader,
        )
        layer.register_parameter("weight", weight)

        input_scale = PerTensorScaleParameter(
            data=torch.empty(len(output_partition_sizes), dtype=torch.float32),
            weight_loader=weight_loader,
        )

        layer.register_parameter("input_scale", input_scale)

        weight_scale_2 = PerTensorScaleParameter(
            data=torch.empty(len(output_partition_sizes), dtype=torch.float32),
            weight_loader=weight_loader,
        )
        layer.register_parameter("weight_scale_2", weight_scale_2)

        group_size = self.quant_config.require_group_size()
        weight_scale = ModelWeightParameter(
            data=torch.empty(
                output_size_per_partition,
                input_size_per_partition // group_size,
                dtype=weight_dtype,
            ),
            input_dim=1,
            output_dim=0,
            weight_loader=weight_loader,
        )

        layer.register_parameter("weight_scale", weight_scale)

    def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
        input_scale_2 = layer.input_scale.max().to(torch.float32)
        weight_scale_2 = layer.weight_scale_2.max().to(torch.float32)
        layer.input_scale = Parameter(input_scale_2, requires_grad=False)
        layer.weight_scale_2 = Parameter(weight_scale_2, requires_grad=False)
        layer.alpha = Parameter(
            layer.input_scale * layer.weight_scale_2, requires_grad=False
        )

        prepare_nvfp4_layer_for_petit(layer)
        del layer.input_scale

    def apply(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        bias: torch.Tensor | None = None,
    ) -> torch.Tensor:
        return apply_petit_nvfp4_linear(
            input=x,
            weight=layer.weight,
            weight_scale=layer.weight_scale,
            weight_scale_2=layer.weight_scale_2,
            size_n=layer.output_size_per_partition,
            size_k=layer.input_size_per_partition,
            bias=bias,
        )