w4afp8.py

from __future__ import annotations

import logging
from typing import TYPE_CHECKING, Any, Dict, List, Optional

import torch
from torch.nn import Module
from torch.nn.parameter import Parameter

from sglang.srt.layers.quantization.base_config import (
    FusedMoEMethodBase,
    QuantizationConfig,
    QuantizeMethodBase,
)
from sglang.srt.layers.quantization.fp8 import Fp8LinearMethod
from sglang.srt.layers.quantization.unquant import UnquantizedLinearMethod
from sglang.srt.layers.quantization.utils import is_layer_skipped
from sglang.srt.utils import set_weight_attrs

if TYPE_CHECKING:
    from sglang.srt.layers.moe.ep_moe.layer import EPMoE, TopKOutput

ACTIVATION_SCHEMES = ["static", "dynamic"]

logger = logging.getLogger(__name__)


class W4AFp8Config(QuantizationConfig):
    """Config class for MIXED_PRECISION W4AFp8."""

    def __init__(
        self,
        is_checkpoint_fp8_serialized: bool = True,
        is_checkpoint_w4afp8_serialized: bool = True,
        linear_activation_scheme: str = "dynamic",
        moe_activation_scheme: str = "static",
        ignored_layers: Optional[List[str]] = None,
        weight_block_size: Optional[List[int]] = None,
        group_size: int = 128,
    ) -> None:
        super().__init__()
        self.is_checkpoint_fp8_serialized = is_checkpoint_fp8_serialized
        self.is_checkpoint_w4afp8_serialized = is_checkpoint_w4afp8_serialized
        if is_checkpoint_w4afp8_serialized:
            logger.warning("Detected w4afp8 checkpoint. Please note that")
        if moe_activation_scheme not in ACTIVATION_SCHEMES:
            raise ValueError(f"Unsupported activation scheme {moe_activation_scheme}")
        self.linear_activation_scheme = linear_activation_scheme
        self.moe_activation_scheme = moe_activation_scheme
        self.ignored_layers = ignored_layers or []
        self.weight_block_size = [128, 128]
        self.group_size = group_size

    @classmethod
    def get_name(cls) -> str:
        return "w4afp8"

    @classmethod
    def get_supported_act_dtypes(cls) -> List[torch.dtype]:
        return [torch.bfloat16, torch.float8_e4m3fn]

    @classmethod
    def get_min_capability(cls) -> int:
        return 90

    @classmethod
    def get_config_filenames(cls) -> List[str]:
        return []

    @classmethod
    def from_config(cls, config: Dict[str, Any]) -> W4AFp8Config:
        quant_method = cls.get_from_keys(config, ["quant_method"])
        is_checkpoint_fp8_serialized = "fp8" in quant_method
        is_checkpoint_w4afp8_serialized = "w4afp8" in quant_method
        linear_activation_scheme = "dynamic"
        moe_activation_scheme = "static"
        weight_block_size = [128, 128]
        return cls(
            is_checkpoint_fp8_serialized=is_checkpoint_fp8_serialized,
            is_checkpoint_w4afp8_serialized=is_checkpoint_w4afp8_serialized,
            linear_activation_scheme=linear_activation_scheme,
            moe_activation_scheme=moe_activation_scheme,
            weight_block_size=weight_block_size,
        )

    def get_quant_method(
        self, layer: torch.nn.Module, prefix: str
    ) -> Optional[QuantizeMethodBase]:
        from sglang.srt.layers.linear import LinearBase
        from sglang.srt.layers.moe.ep_moe.layer import EPMoE
        from sglang.srt.layers.moe.fused_moe_triton import FusedMoE

        if isinstance(layer, LinearBase):
            if is_layer_skipped(prefix, self.ignored_layers):
                return UnquantizedLinearMethod()
            return Fp8LinearMethod(self)
        elif isinstance(layer, EPMoE):
            return W4AFp8MoEMethod(self)
        return None

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


class W4AFp8MoEMethod(FusedMoEMethodBase):

    def __init__(self, quant_config: W4AFp8Config):
        self.quant_config = quant_config

    def create_weights(
        self,
        layer: EPMoE,
        num_experts: int,
        hidden_size: int,
        intermediate_size: int,
        params_dtype: torch.dtype,
        **extra_weight_attrs,
    ):
        assert "weight_loader" in extra_weight_attrs

        # Fused gate_up_proj (column parallel)
        w13_weight = torch.nn.Parameter(
            torch.empty(
                num_experts,
                intermediate_size * 2,
                hidden_size // 2,
                dtype=torch.int8,
            ),
            requires_grad=False,
        )
        layer.register_parameter("w13_weight", w13_weight)
        set_weight_attrs(w13_weight, extra_weight_attrs)

        # down_proj (row parallel)
        w2_weight = torch.nn.Parameter(
            torch.empty(
                num_experts,
                hidden_size,
                intermediate_size // 2,
                dtype=torch.int8,
            ),
            requires_grad=False,
        )
        layer.register_parameter("w2_weight", w2_weight)
        set_weight_attrs(w2_weight, extra_weight_attrs)

        w13_weight_scale = torch.nn.Parameter(
            torch.zeros(
                num_experts,
                2 * intermediate_size,
                hidden_size // self.quant_config.group_size,
                dtype=torch.float32,
            ),
            requires_grad=False,
        )
        layer.register_parameter("w13_weight_scale_inv", w13_weight_scale)
        set_weight_attrs(w13_weight_scale, extra_weight_attrs)

        w2_weight_scale = torch.nn.Parameter(
            torch.zeros(
                num_experts,
                hidden_size,
                intermediate_size // self.quant_config.group_size,
                dtype=torch.float32,
            ),
            requires_grad=False,
        )
        layer.register_parameter("w2_weight_scale_inv", w2_weight_scale)
        set_weight_attrs(w2_weight_scale, extra_weight_attrs)

        # Input scales
        w13_input_scale = torch.nn.Parameter(
            torch.ones((num_experts, 2), dtype=torch.bfloat16),
            requires_grad=False,
        )
        layer.register_parameter("w13_input_scale", w13_input_scale)
        set_weight_attrs(w13_input_scale, extra_weight_attrs)

        w2_input_scale = torch.nn.Parameter(
            torch.ones(num_experts, dtype=torch.bfloat16),
            requires_grad=False,
        )
        layer.register_parameter("w2_input_scale", w2_input_scale)
        set_weight_attrs(w2_input_scale, extra_weight_attrs)

        # Pre-populate the strides
        device = layer.w13_weight.device

        self.a_strides1 = torch.full(
            (num_experts, 3),
            hidden_size,
            device=device,
            dtype=torch.int64,
        )
        self.c_strides1 = torch.full(
            (num_experts, 3),
            2 * intermediate_size,
            device=device,
            dtype=torch.int64,
        )
        self.a_strides2 = torch.full(
            (num_experts, 3),
            intermediate_size,
            device=device,
            dtype=torch.int64,
        )
        self.c_strides2 = torch.full(
            (num_experts, 3),
            hidden_size,
            device=device,
            dtype=torch.int64,
        )
        self.b_strides1 = self.a_strides1
        self.s_strides13 = self.c_strides1
        self.b_strides2 = self.a_strides2
        self.s_strides2 = self.c_strides2

        self.expert_offsets = torch.empty(
            (num_experts + 1), dtype=torch.int32, device=device
        )
        self.problem_sizes1 = torch.empty(
            (num_experts, 3), dtype=torch.int32, device=device
        )
        self.problem_sizes2 = torch.empty(
            (num_experts, 3), dtype=torch.int32, device=device
        )

        return

    def _interleave_scales(self, scales: torch.Tensor) -> torch.Tensor:
        """Interleave scales in groups of 4 similar to TRT-LLM implementation."""
        s_shape = scales.shape
        # Reshape to separate groups of 4
        scales_interleaved = scales.reshape(
            s_shape[0], s_shape[1], (s_shape[2] // 4), 4
        )
        # Permute dimensions to interleave
        scales_interleaved = scales_interleaved.permute(0, 2, 1, 3)
        # Reshape back to original dimensions but with interleaved values
        scales_interleaved = scales_interleaved.reshape(
            s_shape[0], s_shape[2] // 4, s_shape[1] * 4
        )
        return scales_interleaved.contiguous()

    def process_weights_after_loading(self, layer: Module) -> None:
        dtype = torch.bfloat16
        device = layer.w2_weight.device

        # Interleave w13_weight_scale (gate_up_proj)
        w13_weight_scale = layer.w13_weight_scale_inv.to(dtype)
        w13_weight_scale = self._interleave_scales(w13_weight_scale)
        layer.w13_weight_scale_inv = Parameter(w13_weight_scale, requires_grad=False)

        # Interleave w2_weight_scale (down_proj)
        w2_weight_scale = layer.w2_weight_scale_inv.to(dtype)
        w2_weight_scale = self._interleave_scales(w2_weight_scale)
        layer.w2_weight_scale_inv = Parameter(w2_weight_scale, requires_grad=False)

        # Process input scales
        w13_input_scale_max = layer.w13_input_scale.max().to(dtype).item()
        new_w13_input_scale = torch.tensor(
            [w13_input_scale_max],
            dtype=dtype,
            device=device,
        )
        layer.w13_input_scale = Parameter(new_w13_input_scale, requires_grad=False)

        w2_input_scale_max = layer.w2_input_scale.max().to(dtype).item()
        new_w2_input_scale = torch.tensor(
            [w2_input_scale_max], dtype=dtype, device=device
        )
        layer.w2_input_scale = Parameter(new_w2_input_scale, requires_grad=False)

    def apply(
        self,
        layer: EPMoE,
        hidden_states: torch.Tensor,
        topk_output: TopKOutput,
        **kwargs,
    ) -> torch.Tensor:

        # TODO(ch-wan): move it out of this class
        from sglang.srt.layers.moe.cutlass_w4a8_moe import cutlass_w4a8_moe

        topk_weights, topk_ids, _ = topk_output
        local_topk_ids = topk_ids
        if layer.expert_map is not None:
            "Translate info from expert_map to topk_ids"
            local_topk_ids = torch.where(
                layer.expert_map[topk_ids] != layer.num_experts,
                layer.expert_map[topk_ids],
                layer.num_experts,
            )

        return cutlass_w4a8_moe(
            layer.start_expert_id,
            layer.end_expert_id,
            layer.num_experts,
            hidden_states,
            layer.w13_weight,
            layer.w2_weight,
            layer.w13_weight_scale_inv,
            layer.w2_weight_scale_inv,
            topk_weights,
            topk_ids,
            local_topk_ids,
            self.a_strides1,
            self.b_strides1,
            self.c_strides1,
            self.a_strides2,
            self.b_strides2,
            self.c_strides2,
            self.s_strides13,
            self.s_strides2,
            self.expert_offsets,
            self.problem_sizes1,
            self.problem_sizes2,
            layer.w13_input_scale,
            layer.w2_input_scale,
        )