float8_quantize.py

import torch
import torch.nn as nn
from torchao.float8.float8_utils import (
    amax_to_scale,
    tensor_to_amax,
    to_fp8_saturated,
)
from torch.nn import init
import math
from torch.compiler import is_compiling
from torch import __version__
from torch.version import cuda
from typing import TypeVar

IS_TORCH_2_4 = __version__ < (2, 4, 9)
LT_TORCH_2_4 = __version__ < (2, 4)
if LT_TORCH_2_4:
    if not hasattr(torch, "_scaled_mm"):
        raise RuntimeError(
            "This version of PyTorch is not supported. Please upgrade to PyTorch 2.4 with CUDA 12.4 or later."
        )
CUDA_VERSION = float(cuda) if cuda else 0
if CUDA_VERSION < 12.4:
    raise RuntimeError(
        f"This version of PyTorch is not supported. Please upgrade to PyTorch 2.4 with CUDA 12.4 or later got torch version {__version__} and CUDA version {cuda}."
    )
try:
    from cublas_ops import CublasLinear
except ImportError:
    CublasLinear = type(None)


class F8Linear(nn.Module):

    def __init__(
        self,
        in_features: int,
        out_features: int,
        bias: bool = True,
        device=None,
        dtype=torch.float16,
        float8_dtype=torch.float8_e4m3fn,
        float_weight: torch.Tensor = None,
        float_bias: torch.Tensor = None,
        num_scale_trials: int = 24,
        input_float8_dtype=torch.float8_e5m2,
    ) -> None:
        super().__init__()
        self.in_features = in_features
        self.out_features = out_features
        self.float8_dtype = float8_dtype
        self.input_float8_dtype = input_float8_dtype
        self.input_scale_initialized = False
        self.weight_initialized = False
        self.max_value = torch.finfo(self.float8_dtype).max
        self.input_max_value = torch.finfo(self.input_float8_dtype).max
        factory_kwargs = {"dtype": dtype, "device": device}
        if float_weight is None:
            self.weight = nn.Parameter(
                torch.empty((out_features, in_features), **factory_kwargs)
            )
        else:
            self.weight = nn.Parameter(
                float_weight, requires_grad=float_weight.requires_grad
            )
        if float_bias is None:
            if bias:
                self.bias = nn.Parameter(
                    torch.empty(out_features, **factory_kwargs),
                )
            else:
                self.register_parameter("bias", None)
        else:
            self.bias = nn.Parameter(float_bias, requires_grad=float_bias.requires_grad)
        self.num_scale_trials = num_scale_trials
        self.input_amax_trials = torch.zeros(
            num_scale_trials, requires_grad=False, device=device, dtype=torch.float32
        )
        self.trial_index = 0
        self.register_buffer("scale", None)
        self.register_buffer(
            "input_scale",
            None,
        )
        self.register_buffer(
            "float8_data",
            None,
        )
        self.scale_reciprocal = self.register_buffer("scale_reciprocal", None)
        self.input_scale_reciprocal = self.register_buffer(
            "input_scale_reciprocal", None
        )

    def _load_from_state_dict(
        self,
        state_dict,
        prefix,
        local_metadata,
        strict,
        missing_keys,
        unexpected_keys,
        error_msgs,
    ):
        sd = {k.replace(prefix, ""): v for k, v in state_dict.items()}
        if "weight" in sd:
            if (
                "float8_data" not in sd
                or sd["float8_data"] is None
                and sd["weight"].shape == (self.out_features, self.in_features)
            ):
                # Initialize as if it's an F8Linear that needs to be quantized
                self._parameters["weight"] = nn.Parameter(
                    sd["weight"], requires_grad=False
                )
                if "bias" in sd:
                    self._parameters["bias"] = nn.Parameter(
                        sd["bias"], requires_grad=False
                    )
                self.quantize_weight()
            elif sd["float8_data"].shape == (
                self.out_features,
                self.in_features,
            ) and sd["weight"] == torch.zeros_like(sd["weight"]):
                w = sd["weight"]
                # Set the init values as if it's already quantized float8_data
                self.float8_data = sd["float8_data"]
                self._parameters["weight"] = nn.Parameter(
                    torch.zeros(
                        1,
                        dtype=w.dtype,
                        device=w.device,
                        requires_grad=False,
                    )
                )
                if "bias" in sd:
                    self._parameters["bias"] = nn.Parameter(
                        sd["bias"], requires_grad=False
                    )
                self.weight_initialized = True

                # Check if scales and reciprocals are initialized
                if all(
                    key in sd
                    for key in [
                        "scale",
                        "input_scale",
                        "scale_reciprocal",
                        "input_scale_reciprocal",
                    ]
                ):
                    self.scale = sd["scale"].float()
                    self.input_scale = sd["input_scale"].float()
                    self.scale_reciprocal = sd["scale_reciprocal"].float()
                    self.input_scale_reciprocal = sd["input_scale_reciprocal"].float()
                    self.input_scale_initialized = True
                    self.trial_index = self.num_scale_trials
                else:
                    # If scales are not initialized, reset trials
                    self.input_scale_initialized = False
                    self.trial_index = 0
                    self.input_amax_trials = torch.zeros(
                        self.num_scale_trials, requires_grad=False, dtype=torch.float32
                    )
            else:
                raise RuntimeError(
                    f"Weight tensor not found or has incorrect shape in state dict: {sd.keys()}"
                )
        else:
            raise RuntimeError(
                "Weight tensor not found or has incorrect shape in state dict"
            )

    def quantize_weight(self):
        if self.weight_initialized:
            return
        amax = tensor_to_amax(self.weight.data)
        scale = amax_to_scale(amax, self.float8_dtype, self.weight.dtype)
        self.float8_data = to_fp8_saturated(self.weight.data * scale, self.float8_dtype)
        self.scale = scale.float()
        self.weight_initialized = True
        self.scale_reciprocal = self.scale.reciprocal().float()
        self.weight.data = torch.zeros(
            1, dtype=self.weight.dtype, device=self.weight.device, requires_grad=False
        )

    def quantize_input(self, x: torch.Tensor):
        if self.input_scale_initialized:
            return to_fp8_saturated(x * self.input_scale, self.input_float8_dtype)
        elif self.trial_index < self.num_scale_trials:
            amax = tensor_to_amax(x)
            self.input_amax_trials[self.trial_index] = amax
            self.trial_index += 1
            self.input_scale = amax_to_scale(
                self.input_amax_trials[: self.trial_index].max(),
                self.input_float8_dtype,
                self.weight.dtype,
            )
            self.input_scale_reciprocal = self.input_scale.reciprocal()
            return to_fp8_saturated(x * self.input_scale, self.input_float8_dtype)
        else:
            self.input_scale = amax_to_scale(
                self.input_amax_trials.max(), self.input_float8_dtype, self.weight.dtype
            )
            self.input_scale_reciprocal = self.input_scale.reciprocal()
            self.input_scale_initialized = True
            return to_fp8_saturated(x * self.input_scale, self.input_float8_dtype)

    def reset_parameters(self) -> None:
        if self.weight_initialized:
            self.weight = nn.Parameter(
                torch.empty(
                    (self.out_features, self.in_features),
                    **{
                        "dtype": self.weight.dtype,
                        "device": self.weight.device,
                    },
                )
            )
            self.weight_initialized = False
            self.input_scale_initialized = False
            self.trial_index = 0
            self.input_amax_trials.zero_()
        init.kaiming_uniform_(self.weight, a=math.sqrt(5))
        if self.bias is not None:
            fan_in, _ = init._calculate_fan_in_and_fan_out(self.weight)
            bound = 1 / math.sqrt(fan_in) if fan_in > 0 else 0
            init.uniform_(self.bias, -bound, bound)
        self.quantize_weight()
        self.max_value = torch.finfo(self.float8_dtype).max
        self.input_max_value = torch.finfo(self.input_float8_dtype).max

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        if self.input_scale_initialized or is_compiling():
            x = (
                x.mul(self.input_scale)
                .clamp(min=-self.input_max_value, max=self.input_max_value)
                .type(self.input_float8_dtype)
            )
        else:
            x = self.quantize_input(x)

        prev_dims = x.shape[:-1]
        x = x.view(-1, self.in_features)

        # float8 matmul, much faster than float16 matmul w/ float32 accumulate on ADA devices!
        out = torch._scaled_mm(
            x,
            self.float8_data.T,
            scale_a=self.input_scale_reciprocal,
            scale_b=self.scale_reciprocal,
            bias=self.bias,
            out_dtype=self.weight.dtype,
            use_fast_accum=True,
        )
        if IS_TORCH_2_4:
            out = out[0]
        out = out.view(*prev_dims, self.out_features)
        return out

    @classmethod
    def from_linear(
        cls,
        linear: nn.Linear,
        float8_dtype=torch.float8_e4m3fn,
        input_float8_dtype=torch.float8_e5m2,
    ) -> "F8Linear":
        f8_lin = cls(
            in_features=linear.in_features,
            out_features=linear.out_features,
            bias=linear.bias is not None,
            device=linear.weight.device,
            dtype=linear.weight.dtype,
            float8_dtype=float8_dtype,
            float_weight=linear.weight.data,
            float_bias=(linear.bias.data if linear.bias is not None else None),
            input_float8_dtype=input_float8_dtype,
        )
        f8_lin.quantize_weight()
        return f8_lin


def recursive_swap_linears(
    model: nn.Module,
    float8_dtype=torch.float8_e4m3fn,
    input_float8_dtype=torch.float8_e5m2,
) -> None:
    """
    Recursively swaps all nn.Linear modules in the given model with F8Linear modules.

    This function traverses the model's structure and replaces each nn.Linear
    instance with an F8Linear instance, which uses 8-bit floating point
    quantization for weights. The original linear layer's weights are deleted
    after conversion to save memory.

    Args:
        model (nn.Module): The PyTorch model to modify.

    Note:
        This function modifies the model in-place. After calling this function,
        all linear layers in the model will be using 8-bit quantization.
    """
    for name, child in model.named_children():
        if isinstance(child, nn.Linear) and not isinstance(
            child, (F8Linear, CublasLinear)
        ):

            setattr(
                model,
                name,
                F8Linear.from_linear(
                    child,
                    float8_dtype=float8_dtype,
                    input_float8_dtype=input_float8_dtype,
                ),
            )
            del child
        else:
            recursive_swap_linears(child)


@torch.inference_mode()
def quantize_flow_transformer_and_dispatch_float8(
    flow_model: nn.Module,
    device=torch.device("cuda"),
    float8_dtype=torch.float8_e4m3fn,
    input_float8_dtype=torch.float8_e5m2,
    offload_flow=False,
) -> nn.Module:
    """
    Quantize the flux flow transformer model (original BFL codebase version) and dispatch to the given device.

    Iteratively pushes each module to device, evals, replaces linear layers with F8Linear except for final_layer, and quantizes.

    Allows for fast dispatch to gpu & quantize without causing OOM on gpus with limited memory.

    After dispatching, if offload_flow is True, offloads the model to cpu.
    """
    for module in flow_model.double_blocks:
        module.to(device)
        module.eval()
        recursive_swap_linears(
            module, float8_dtype=float8_dtype, input_float8_dtype=input_float8_dtype
        )
        torch.cuda.empty_cache()
    for module in flow_model.single_blocks:
        module.to(device)
        module.eval()
        recursive_swap_linears(
            module, float8_dtype=float8_dtype, input_float8_dtype=input_float8_dtype
        )
        torch.cuda.empty_cache()
    to_gpu_extras = [
        "vector_in",
        "img_in",
        "txt_in",
        "time_in",
        "guidance_in",
        "final_layer",
        "pe_embedder",
    ]
    for module in to_gpu_extras:
        m_extra = getattr(flow_model, module)
        if m_extra is None:
            continue
        m_extra.to(device)
        m_extra.eval()
        if isinstance(m_extra, nn.Linear) and not isinstance(
            m_extra, (F8Linear, CublasLinear)
        ):
            setattr(
                flow_model,
                module,
                F8Linear.from_linear(
                    m_extra,
                    float8_dtype=float8_dtype,
                    input_float8_dtype=input_float8_dtype,
                ),
            )
            del m_extra
        elif module != "final_layer":
            recursive_swap_linears(
                m_extra,
                float8_dtype=float8_dtype,
                input_float8_dtype=input_float8_dtype,
            )
        torch.cuda.empty_cache()
    if offload_flow:
        flow_model.to("cpu")
        torch.cuda.empty_cache()
    return flow_model