vllm/vllm/model_executor/layers/quantization/utils/fp8_utils.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

# Adapted from https://github.com/sgl-project/sglang/pull/2575
import functools
import json
import os
from collections.abc import Sequence
from typing import Any, Callable, Optional, Union

import torch

import vllm.envs as envs
from vllm import _custom_ops as ops
from vllm.logger import init_logger
from vllm.model_executor.layers.quantization.utils.quant_utils import (
    group_broadcast)
from vllm.model_executor.layers.quantization.utils.w8a8_utils import (
    CUTLASS_BLOCK_FP8_SUPPORTED)
from vllm.platforms import current_platform
from vllm.triton_utils import tl, triton
from vllm.utils import cdiv, direct_register_custom_op
from vllm.utils.deep_gemm import (is_deep_gemm_e8m0_used,
                                  should_use_deepgemm_for_fp8_linear)

logger = init_logger(__name__)


def is_fp8(x: Union[torch.dtype, torch.Tensor]) -> bool:
    if isinstance(x, torch.Tensor):
        x = x.dtype
    return x == torch.float8_e4m3fn or x == torch.float8_e4m3fnuz


def cutlass_scaled_mm(
    A: torch.Tensor,
    B: torch.Tensor,
    As: torch.Tensor,
    Bs: torch.Tensor,
    block_size: list[int],
    output_dtype: torch.dtype = torch.float16,
) -> torch.Tensor:
    return ops.cutlass_scaled_mm(
        A,
        B.T,
        out_dtype=output_dtype,
        scale_a=As,
        # SM90 block FP8 requires row-major scale_b, which we do ahead of time
        scale_b=Bs if block_size is not None
        and current_platform.is_device_capability(90) else Bs.T)


def rocm_aiter_gemm_w8a8_blockscale_impl(
    A: torch.Tensor,
    B: torch.Tensor,
    As: torch.Tensor,
    Bs: torch.Tensor,
    block_size: list[int],
    output_dtype: torch.dtype = torch.float16,
) -> torch.Tensor:
    import aiter as rocm_aiter

    return rocm_aiter.gemm_a8w8_blockscale(A, B, As, Bs, dtype=output_dtype)


def rocm_aiter_gemm_w8a8_blockscale_fake(
    A: torch.Tensor,
    B: torch.Tensor,
    As: torch.Tensor,
    Bs: torch.Tensor,
    block_size: list[int],
    output_dtype: torch.dtype = torch.float16,
) -> torch.Tensor:

    m = A.shape[0]
    n = B.shape[0]
    Y = torch.empty(m, n, dtype=output_dtype, device=A.device)
    return Y


if current_platform.is_rocm():
    direct_register_custom_op(
        op_name="rocm_aiter_gemm_w8a8_blockscale",
        op_func=rocm_aiter_gemm_w8a8_blockscale_impl,
        mutates_args=[],
        fake_impl=rocm_aiter_gemm_w8a8_blockscale_fake,
        dispatch_key=current_platform.dispatch_key,
    )
    if (envs.VLLM_ROCM_USE_AITER and envs.VLLM_ROCM_USE_AITER_LINEAR
            and current_platform.is_fp8_fnuz()):

        import aiter as rocm_aiter
        from aiter import get_hip_quant

        aiter_per1x128_quant = get_hip_quant(rocm_aiter.QuantType.per_1x128)


def dispatch_w8a8_blockscale_func(
    use_cutlass: bool, use_aiter_and_is_supported: bool
) -> Callable[[
        torch.Tensor,
        torch.Tensor,
        torch.Tensor,
        torch.Tensor,
        list[int],
        torch.dtype,
], torch.Tensor]:
    if use_cutlass:
        return cutlass_scaled_mm
    if (use_aiter_and_is_supported):
        return torch.ops.vllm.rocm_aiter_gemm_w8a8_blockscale
    return w8a8_block_fp8_matmul


# TODO fix ROCm->Triton custom path:
#  https://github.com/vllm-project/vllm/issues/14397
def apply_w8a8_block_fp8_linear(
    input: torch.Tensor,
    weight: torch.Tensor,
    block_size: list[int],
    weight_scale: torch.Tensor,
    input_scale: Optional[torch.Tensor] = None,
    bias: Optional[torch.Tensor] = None,
    cutlass_block_fp8_supported: bool = CUTLASS_BLOCK_FP8_SUPPORTED,
    use_aiter_and_is_supported: bool = False,
) -> torch.Tensor:
    assert input_scale is None
    # View input as 2D matrix for fp8 methods
    input_2d = input.view(-1, input.shape[-1])
    output_shape = [*input.shape[:-1], weight.shape[0]]
    output_dtype = input.dtype

    if should_use_deepgemm_for_fp8_linear(output_dtype, weight):

        input_2d = input.view(-1, input.shape[-1])
        output_shape = [*input.shape[:-1], weight.shape[0]]

        q_input, x_scale = per_token_group_quant_fp8(
            input_2d,
            block_size[1],
            column_major_scales=True,
        )

        # ensure DeepGEMM-backed custom op is registered before use
        import vllm.model_executor.layers.quantization.deepgemm  # noqa: F401

        output = torch.ops.vllm.w8a8_block_fp8_matmul_deepgemm(
            q_input,
            weight,
            x_scale,
            weight_scale,
            block_size,
            output_dtype=output_dtype)
        if bias is not None:
            output += bias
        return output.to(dtype=output_dtype).view(*output_shape)

    w8a8_blockscale_func = dispatch_w8a8_blockscale_func(
        cutlass_block_fp8_supported, use_aiter_and_is_supported)
    if cutlass_block_fp8_supported:
        num_pad = 0
        if current_platform.is_device_capability(90):
            # pad first dimension to be divisible by 4 due to
            # cutlass blockwise gemm limitation for hopper
            num_pad = 4 - (input_2d.shape[0] % 4)
            if num_pad > 0:
                input_2d = torch.nn.functional.pad(input_2d,
                                                   (0, 0, 0, num_pad),
                                                   "constant", 0)
        q_input, x_scale = per_token_group_quant_fp8(input_2d,
                                                     block_size[1],
                                                     column_major_scales=True)
        output = w8a8_blockscale_func(q_input, weight, x_scale, weight_scale,
                                      block_size, input.dtype)
        if num_pad > 0:
            output = output[:-num_pad]
    else:
        if use_aiter_and_is_supported:
            q_input, x_scale = aiter_per1x128_quant(
                input_2d.contiguous(), quant_dtype=rocm_aiter.dtypes.fp8)
        else:
            q_input, x_scale = per_token_group_quant_fp8(
                input_2d, block_size[1], column_major_scales=False)

        output = w8a8_blockscale_func(q_input, weight, x_scale, weight_scale,
                                      block_size, input.dtype)

    if bias is not None:
        output = output + bias
    return output.to(dtype=input.dtype).view(*output_shape)


def apply_w8a8_block_fp8_linear_fake(
    input: torch.Tensor,
    weight: torch.Tensor,
    block_size: list[int],
    weight_scale: torch.Tensor,
    input_scale: Optional[torch.Tensor] = None,
    bias: Optional[torch.Tensor] = None,
    cutlass_block_fp8_supported: bool = CUTLASS_BLOCK_FP8_SUPPORTED,
    use_aiter_and_is_supported: bool = False,
) -> torch.Tensor:
    output_shape = [*input.shape[:-1], weight.shape[0]]
    return torch.empty(output_shape, dtype=input.dtype, device=input.device)


if not current_platform.is_cpu():
    direct_register_custom_op(
        op_name="apply_w8a8_block_fp8_linear",
        op_func=apply_w8a8_block_fp8_linear,
        mutates_args=[],
        fake_impl=apply_w8a8_block_fp8_linear_fake,
    )


def input_to_float8(
        x: torch.Tensor,
        dtype: Optional[torch.dtype] = None
) -> tuple[torch.Tensor, torch.Tensor]:
    """This function quantizes input values to float8 values "
    "with tensor-wise quantization."""
    dtype = current_platform.fp8_dtype() if dtype is None else dtype
    finfo = torch.finfo(dtype)
    min_val, max_val = x.aminmax()
    amax = torch.maximum(min_val.abs(), max_val.abs()).clamp(min=1e-12)
    scale = finfo.max / amax
    x_scl_sat = (x * scale).clamp(min=finfo.min, max=finfo.max)
    return x_scl_sat.to(dtype).contiguous(), scale.float().reciprocal()


def block_quant_to_tensor_quant(
    x_q_block: torch.Tensor,
    x_s: torch.Tensor,
) -> tuple[torch.Tensor, torch.Tensor]:
    """This function converts block-wise quantization to tensor-wise
    quantization. The inputs are block-wise quantization tensor `x_q_block`,
    block-wise quantization scale and the block size.
    The outputs are tensor-wise quantization tensor and tensor-wise
    quantization scale. Note only float8 is supported for now.
    """
    x_dq_block = group_broadcast(x_q_block, x_s)
    x_q_tensor, scale = input_to_float8(x_dq_block, dtype=x_q_block.dtype)
    return x_q_tensor, scale


@triton.jit
def _per_token_group_quant_fp8(
    # Pointers to inputs and output
    y_ptr,
    y_q_ptr,
    y_s_ptr,
    group_size,
    # Num columns of y
    y_num_columns,
    y_row_stride,
    # Avoid to divide zero
    eps,
    # Information for float8
    fp8_min,
    fp8_max,
    use_ue8m0: tl.constexpr,
    # Meta-parameters
    BLOCK: tl.constexpr,
):
    """A Triton-accelerated function to perform per-token-group
    quantization on a tensor.
    This function converts the tensor values into float8 values.
    """
    groups_per_row = y_num_columns // group_size

    # Map the program id to the row of X and Y it should compute.
    g_id = tl.program_id(0)
    row = g_id // groups_per_row
    row_g_id = g_id % groups_per_row

    # Ensure offset calculations use int64 to prevent overflow
    y_ptr_offset = (row.to(tl.int64) * y_row_stride) + (row_g_id.to(tl.int64) *
                                                        group_size)
    y_ptr += y_ptr_offset

    y_q_ptr_offset = g_id.to(tl.int64) * group_size
    y_q_ptr += y_q_ptr_offset
    y_s_ptr += g_id

    cols = tl.arange(0, BLOCK)  # N <= BLOCK
    mask = cols < group_size

    y = tl.load(y_ptr + cols, mask=mask, other=0.0).to(tl.float32)
    # Quant
    _absmax = tl.maximum(tl.max(tl.abs(y)), eps)
    scale_raw = _absmax / fp8_max
    y_s = tl.math.exp2(tl.ceil(tl.log2(scale_raw))) if use_ue8m0 else scale_raw
    y_q = tl.clamp(y / y_s, fp8_min, fp8_max).to(y_q_ptr.dtype.element_ty)

    tl.store(y_q_ptr + cols, y_q, mask=mask)
    tl.store(y_s_ptr, y_s)


@triton.jit
def _per_token_group_quant_fp8_colmajor(
    # Pointers to inputs and output
    y_ptr,
    y_q_ptr,
    y_s_ptr,
    group_size,
    # Num columns of y
    y_num_columns,
    y_row_stride,
    # Stride from one column to the next of y_s
    y_s_col_stride,
    # Avoid to divide zero
    eps,
    # Information for float8
    fp8_min,
    fp8_max,
    use_ue8m0: tl.constexpr,
    # Meta-parameters
    BLOCK: tl.constexpr,
):
    """A Triton-accelerated function to perform per-token-group
    quantization on a tensor.
    This function converts the tensor values into float8 values.
    """
    groups_per_row = y_num_columns // group_size

    # Map the program id to the row of X and Y it should compute.
    g_id = tl.program_id(0)
    row = g_id // groups_per_row
    row_g_id = g_id % groups_per_row

    # Ensure offset calculations use int64 to prevent overflow
    y_ptr_offset = (row.to(tl.int64) * y_row_stride) + (row_g_id.to(tl.int64) *
                                                        group_size)
    y_ptr += y_ptr_offset

    y_q_ptr_offset = g_id.to(tl.int64) * group_size
    y_q_ptr += y_q_ptr_offset

    # Convert g_id the flattened block coordinate to 2D so we can index
    # into the output y_scales matrix
    blocks_per_row = y_num_columns // group_size
    scale_col = g_id % blocks_per_row
    scale_row = g_id // blocks_per_row
    # Ensure offset calculation uses int64 for y_s_ptr
    y_s_ptr_offset = (scale_col.to(tl.int64) * y_s_col_stride) + scale_row.to(
        tl.int64)
    y_s_ptr += y_s_ptr_offset

    cols = tl.arange(0, BLOCK)  # group_size <= BLOCK
    mask = cols < group_size

    y = tl.load(y_ptr + cols, mask=mask, other=0.0).to(tl.float32)
    # Quant
    _absmax = tl.maximum(tl.max(tl.abs(y)), eps)
    scale_raw = _absmax / fp8_max
    y_s = tl.math.exp2(tl.ceil(tl.log2(scale_raw))) if use_ue8m0 else scale_raw
    y_q = tl.clamp(y / y_s, fp8_min, fp8_max).to(y_q_ptr.dtype.element_ty)

    tl.store(y_q_ptr + cols, y_q, mask=mask)
    tl.store(y_s_ptr, y_s)


def per_token_group_quant_fp8(
    x: torch.Tensor,
    group_size: int,
    eps: float = 1e-10,
    dtype: Optional[torch.dtype] = None,
    column_major_scales: bool = False,
    out_q: Optional[torch.Tensor] = None,
    use_ue8m0: Optional[bool] = None,
) -> tuple[torch.Tensor, torch.Tensor]:
    """Function to perform per-token-group quantization on an input tensor `x`.
    It converts the tensor values into signed float8 values and returns the
    quantized tensor along with the scaling factor used for quantization.
    Args:
        x: The input tensor with ndim >= 2.
        group_size: The group size used for quantization.
        eps: The minimum to avoid dividing zero.
        dtype: The dype of output tensor. Note that only `torch.float8_e4m3fn`
        is supported for now.
        column_major_scales: Outputs scales in column major.
        out_q: Optional output tensor. If not provided, function will create.
    Returns:
        tuple[torch.Tensor, torch.Tensor]: The quantized tensor and the
        scaling factor.
    """
    if use_ue8m0 is None:
        use_ue8m0 = is_deep_gemm_e8m0_used()
    dtype = current_platform.fp8_dtype() if dtype is None else dtype
    assert (x.shape[-1] % group_size == 0), (
        f"the last dimension of `x` {x.shape[-1]} must be divisible "
        f"by `group_size` {group_size}")
    assert x.stride(-1) == 1, "`x` groups must be contiguous"

    finfo = torch.finfo(dtype)
    fp8_min = finfo.min
    fp8_max = finfo.max

    assert out_q is None or out_q.shape == x.shape
    x_q = out_q
    if x_q is None:
        x_q = torch.empty_like(x, device=x.device, dtype=dtype)

    # Allocate the scale tensor in either row- or column-major format.
    if column_major_scales:
        shape = (x.shape[-1] // group_size, ) + x.shape[:-1]
        x_s = torch.empty(shape, device=x.device,
                          dtype=torch.float32).permute(-1, -2)
    else:
        shape = x.shape[:-1] + (x.shape[-1] // group_size, )
        x_s = torch.empty(shape, device=x.device, dtype=torch.float32)

    # prefer CUDA kernel if available
    if current_platform.is_cuda() and x.is_contiguous():
        torch.ops._C.per_token_group_fp8_quant(x, x_q, x_s, group_size, eps,
                                               fp8_min, fp8_max, use_ue8m0)
        return x_q, x_s

    # TRITON FALLBACK
    M = x.numel() // group_size
    N = group_size
    BLOCK = triton.next_power_of_2(N)
    # heuristics for number of warps
    num_warps = min(max(BLOCK // 256, 1), 8)
    num_stages = 1
    if column_major_scales:
        _per_token_group_quant_fp8_colmajor[(M, )](
            x,
            x_q,
            x_s,
            group_size,
            x.shape[1],
            x.stride(0),
            x_s.stride(1),
            eps,
            fp8_min=fp8_min,
            fp8_max=fp8_max,
            use_ue8m0=use_ue8m0,
            BLOCK=BLOCK,
            num_warps=num_warps,
            num_stages=num_stages,
        )
    else:
        _per_token_group_quant_fp8[(M, )](
            x,
            x_q,
            x_s,
            group_size,
            x.shape[1],
            x.stride(0),
            eps,
            fp8_min=fp8_min,
            fp8_max=fp8_max,
            use_ue8m0=use_ue8m0,
            BLOCK=BLOCK,
            num_warps=num_warps,
            num_stages=num_stages,
        )

    return x_q, x_s


@triton.jit
def _w8a8_block_fp8_matmul(
    # Pointers to inputs and output
    A,
    B,
    C,
    As,
    Bs,
    # Shape for matmul
    M,
    N,
    K,
    # Block size for block-wise quantization
    group_n,
    group_k,
    # Stride for inputs and output
    stride_am,
    stride_ak,
    stride_bk,
    stride_bn,
    stride_cm,
    stride_cn,
    stride_As_m,
    stride_As_k,
    stride_Bs_k,
    stride_Bs_n,
    # Meta-parameters
    BLOCK_SIZE_M: tl.constexpr,
    BLOCK_SIZE_N: tl.constexpr,
    BLOCK_SIZE_K: tl.constexpr,
    GROUP_SIZE_M: tl.constexpr,
):
    """Triton-accelerated function used to perform linear operations (dot
    product) on input tensors `A` and `B` with block-wise quantization, and
    store the result in output tensor `C`.
    """

    pid = tl.program_id(axis=0)
    num_pid_m = tl.cdiv(M, BLOCK_SIZE_M)
    num_pid_n = tl.cdiv(N, BLOCK_SIZE_N)
    num_pid_in_group = GROUP_SIZE_M * num_pid_n
    group_id = pid // num_pid_in_group
    first_pid_m = group_id * GROUP_SIZE_M
    group_size_m = min(num_pid_m - first_pid_m, GROUP_SIZE_M)
    pid_m = first_pid_m + (pid % group_size_m)
    pid_n = (pid % num_pid_in_group) // group_size_m

    offs_am = (pid_m * BLOCK_SIZE_M + tl.arange(0, BLOCK_SIZE_M)) % M
    offs_bn = (pid_n * BLOCK_SIZE_N + tl.arange(0, BLOCK_SIZE_N)) % N
    offs_k = tl.arange(0, BLOCK_SIZE_K)
    a_ptrs = A + (offs_am[:, None] * stride_am + offs_k[None, :] * stride_ak)
    b_ptrs = B + (offs_k[:, None] * stride_bk + offs_bn[None, :] * stride_bn)

    As_ptrs = As + offs_am * stride_As_m
    offs_bsn = offs_bn // group_n
    Bs_ptrs = Bs + offs_bsn * stride_Bs_n

    accumulator = tl.zeros((BLOCK_SIZE_M, BLOCK_SIZE_N), dtype=tl.float32)
    for k in range(0, tl.cdiv(K, BLOCK_SIZE_K)):
        a = tl.load(a_ptrs,
                    mask=offs_k[None, :] < K - k * BLOCK_SIZE_K,
                    other=0.0)
        b = tl.load(b_ptrs,
                    mask=offs_k[:, None] < K - k * BLOCK_SIZE_K,
                    other=0.0)

        k_start = k * BLOCK_SIZE_K
        offs_ks = k_start // group_k
        a_s = tl.load(As_ptrs + offs_ks * stride_As_k)
        b_s = tl.load(Bs_ptrs + offs_ks * stride_Bs_k)

        accumulator += tl.dot(a, b) * a_s[:, None] * b_s[None, :]
        a_ptrs += BLOCK_SIZE_K * stride_ak
        b_ptrs += BLOCK_SIZE_K * stride_bk

    if C.dtype.element_ty == tl.bfloat16:
        c = accumulator.to(tl.bfloat16)
    elif C.dtype.element_ty == tl.float16:
        c = accumulator.to(tl.float16)
    else:
        c = accumulator.to(tl.float32)

    offs_cm = pid_m * BLOCK_SIZE_M + tl.arange(0, BLOCK_SIZE_M)
    offs_cn = pid_n * BLOCK_SIZE_N + tl.arange(0, BLOCK_SIZE_N)
    c_ptrs = C + stride_cm * offs_cm[:, None] + stride_cn * offs_cn[None, :]
    c_mask = (offs_cm[:, None] < M) & (offs_cn[None, :] < N)
    tl.store(c_ptrs, c, mask=c_mask)


@functools.lru_cache
def get_w8a8_block_fp8_configs(N: int, K: int, block_n: int,
                               block_k: int) -> Optional[dict[int, Any]]:
    """
    Return optimized configurations for the w8a8 block fp8 kernel.
    The return value will be a dictionary that maps an irregular grid of
    batch sizes to configurations of the w8a8 block fp8 kernel. To evaluate the
    kernel on a given batch size bs, the closest batch size in the grid should
    be picked and the associated configuration chosen to invoke the kernel.
    """

    # First look up if an optimized configuration is available in the configs
    # directory
    device_name = current_platform.get_device_name().replace(" ", "_")
    json_file_name = f"N={N},K={K},device_name={device_name},dtype=fp8_w8a8,block_shape=[{block_n},{block_k}].json"  # noqa: E501

    config_file_path = os.path.join(
        os.path.dirname(os.path.realpath(__file__)), "configs", json_file_name)
    if os.path.exists(config_file_path):
        with open(config_file_path) as f:
            logger.info(
                "Using configuration from %s for W8A8 Block FP8 kernel.",
                config_file_path,
            )
            # If a configuration has been found, return it
            return {int(key): val for key, val in json.load(f).items()}

    # If no optimized configuration is available, we will use the default
    # configuration
    logger.warning(
        "Using default W8A8 Block FP8 kernel config. Performance might "
        "be sub-optimal! Config file not found at %s",
        config_file_path,
    )
    return None


def w8a8_block_fp8_matmul(
    A: torch.Tensor,
    B: torch.Tensor,
    As: torch.Tensor,
    Bs: torch.Tensor,
    block_size: list[int],
    output_dtype: torch.dtype = torch.float16,
) -> torch.Tensor:
    """This function performs matrix multiplication with block-wise
    quantization.
    It takes two input tensors `A` and `B` with scales `As` and `Bs`.
    The output is returned in the specified `output_dtype`.
    Args:
        A: The input tensor, e.g., activation.
        B: The input tensor, e.g., weight.
        As: The per-token-group quantization scale for `A`.
        Bs: The per-block quantization scale for `B`.
        block_size: The block size for per-block quantization. It should
        be 2-dim, e.g., [128, 128].
        output_dytpe: The dtype of the returned tensor.
    Returns:
        torch.Tensor: The result of matmul.
    """
    assert len(block_size) == 2
    block_n, block_k = block_size[0], block_size[1]

    assert A.shape[-1] == B.shape[-1]
    assert A.shape[:-1] == As.shape[:-1] and A.is_contiguous()
    assert triton.cdiv(A.shape[-1], block_k) == As.shape[-1]
    M = A.numel() // A.shape[-1]

    assert B.ndim == 2 and Bs.ndim == 2
    N, K = B.shape
    assert triton.cdiv(N, block_n) == Bs.shape[0]
    assert triton.cdiv(K, block_k) == Bs.shape[1]

    C_shape = A.shape[:-1] + (N, )
    C = A.new_empty(C_shape, dtype=output_dtype)

    configs = get_w8a8_block_fp8_configs(N, K, block_size[0], block_size[1])
    if configs:
        # Get the optimal config if there is one
        config = configs[min(configs.keys(), key=lambda x: abs(x - M))]
    else:
        # Default config
        # Block-wise quant: BLOCK_SIZE_N must be divisible by block_size[0]
        # BLOCK_SIZE_K must be divisible by block_size[1]
        config = {
            "BLOCK_SIZE_M": 64,
            "BLOCK_SIZE_N": block_size[0],
            "BLOCK_SIZE_K": block_size[1],
            "GROUP_SIZE_M": 32,
            "num_warps": 4,
            "num_stages": 2,
        }

    def grid(META):
        return (triton.cdiv(M, META["BLOCK_SIZE_M"]) *
                triton.cdiv(N, META["BLOCK_SIZE_N"]), )

    _w8a8_block_fp8_matmul[grid](
        A,
        B,
        C,
        As,
        Bs,
        M,
        N,
        K,
        block_n,
        block_k,
        A.stride(-2),
        A.stride(-1),
        B.stride(1),
        B.stride(0),
        C.stride(-2),
        C.stride(-1),
        As.stride(-2),
        As.stride(-1),
        Bs.stride(1),
        Bs.stride(0),
        **config,
    )

    return C


# Taken from https://github.com/deepseek-ai/DeepGEMM/blob/0c88cd01392c1073c7049a97d6328c7bba9b3947
# TODO(wentao): remove this function when DeepGEMM exposes this function
def get_tma_aligned_size(x: int, element_size: int) -> int:
    """
    Global memory address of TMA must be 16-byte aligned.
    Since we use column-major layout for the LHS scaling tensor,
        the M-axis of the LHS scaling tensor needs to be padded to a multiple of
        16 bytes.

    Arguments:
        x: original M-axis shape of the LHS scaling tensor.
        element_size: element size of the LHS scaling tensor.

    Returns:
        M-axis shape of the LHS scaling tensor after padding.
    """
    tma_alignment_bytes = 16
    assert tma_alignment_bytes % element_size == 0
    alignment = tma_alignment_bytes // element_size
    return cdiv(x, alignment) * alignment


# Taken from https://github.com/deepseek-ai/DeepGEMM/blob/0c88cd01392c1073c7049a97d6328c7bba9b3947
# TODO(wentao): remove this function when DeepGEMM exposes this function
def get_col_major_tma_aligned_tensor(x: torch.Tensor) -> torch.Tensor:
    """
    Returns TMA-aligned transposed format of the input tensor. `torch.transpose`
        will be called if necessary.
    If the input tensor is already column-major layout and 16-byte aligned along
        the M axis (thus meets the requirement of LHS scaling tensor in
        DeepGEMM), this function will do nothing.

    Arguments:
        x: usually the LHS scaling tensor in GEMM.

    Returns:
        The LHS scaling tensor of TMA-aligned transposed format.
    """
    # NOTES: for the extreme performance, you may rewrite/fuse this function in
    # CUDA
    assert x.dim() in (2, 3)
    remove_dim = False
    m, n = x.shape[-2], x.shape[-1]
    aligned_m = get_tma_aligned_size(m, x.element_size())
    if x.dim() == 2:
        if x.stride(0) == 1 and x.stride(1) == aligned_m:
            return x
        x, remove_dim = x.unsqueeze(0), True

    b = x.shape[0]

    # The last kernel gives a column-major TMA aligned layout
    if x.stride(0) == aligned_m * n and x.stride(1) == 1 and x.stride(
            2) == aligned_m:
        return x.squeeze(0) if remove_dim else x

    # Normal layout requires transposing
    aligned_x = torch.transpose(
        torch.empty((b, n, aligned_m), device=x.device, dtype=x.dtype), 1, 2)
    aligned_x[:, :m, :] = x
    aligned_x = aligned_x[:, :m, :]
    return aligned_x.squeeze(0) if remove_dim else aligned_x


def requant_weight_ue8m0_inplace(
        weight: torch.Tensor,
        weight_scale: torch.Tensor,
        block_size: Sequence[int] = (128, 128),
) -> None:
    """Re-quantise *weight* so that its per-block scaling factors are in the
    UE8M0 (power-of-two) format expected by the new DeepGEMM kernels inplace.

    Args:
        weight: Block-quantised weight tensor stored in ``torch.float8_e4m3fn``.
            Expected shape ``(..., M, K)``.
        weight_scale: Corresponding per-block scale tensor (``torch.float32``)
            with shape ``(..., M // block_size[0], K // block_size[1])``.
        block_size: 2-element iterable ``[block_m, block_k]`` describing the
            block quantisation granularity.
    """
    if weight.numel() == 0:
        return

    if weight.dtype != torch.float8_e4m3fn:
        raise ValueError("Expected *weight* to be torch.float8_e4m3fn, got "
                         f"{weight.dtype} instead.")

    from vllm.utils.deep_gemm import per_block_cast_to_fp8

    block_m, block_k = int(block_size[0]), int(block_size[1])

    # Flatten leading dimensions so we can iterate over the last two dims.
    leading_shape = weight.shape[:-2]
    if len(leading_shape) == 0:
        w_view = weight.unsqueeze(0)
        s_view = weight_scale.unsqueeze(0)
    else:
        w_view = weight.reshape(-1, weight.shape[-2], weight.shape[-1])
        s_view = weight_scale.reshape(-1, *weight_scale.shape[-2:])

    num_mats = w_view.size(0)
    for idx in range(num_mats):
        w_q = w_view[idx]
        s_old = s_view[idx]

        # De-quantise with the *old* scaling factors (float32).
        m_cur, k_cur = w_q.shape
        s_float = s_old.to(torch.float32)
        # Expand scales along rows and cols by block size, then crop.
        s_exp_r = torch.repeat_interleave(s_float, block_m, dim=0)
        s_exp = torch.repeat_interleave(s_exp_r, block_k, dim=1)
        s_exp = s_exp[:m_cur, :k_cur]
        w_dq = w_q.to(torch.float32) * s_exp
        # Re-quantise using power-of-two scaling (UE8M0).
        w_requant, s_requant = per_block_cast_to_fp8(w_dq, [block_m, block_k],
                                                     use_ue8m0=True)

        # Write back the results in-place.
        w_q.copy_(w_requant)
        s_old.copy_(s_requant)