vllm.model_executor.layers.batch_invariant ¶

@triton.jit
def _log_softmax_kernel(
    input_ptr,
    output_ptr,
    input_row_stride,
    output_row_stride,
    n_cols,
    BLOCK_SIZE: tl.constexpr,
):
    """
    Compute log_softmax along the last dimension of a 2D tensor.
    Each block handles one row of the input tensor.
    """
    # Get the row index for this block
    row_idx = tl.program_id(0).to(tl.int64)

    # Compute base pointers for input and output rows
    row_start_ptr = input_ptr + row_idx * input_row_stride
    output_row_start_ptr = output_ptr + row_idx * output_row_stride

    # Step 1: Find maximum value in the row for numerical stability
    max_val = -float("inf")
    for col_offset in range(0, n_cols, BLOCK_SIZE):
        col_idx = col_offset + tl.arange(0, BLOCK_SIZE)
        mask = col_idx < n_cols

        # Load values
        vals = tl.load(row_start_ptr + col_idx, mask=mask, other=-float("inf"))

        # Update maximum
        max_val = tl.max(tl.maximum(vals, max_val))

    # Step 2: Compute sum of exp(x - max_val)
    sum_exp = 0.0
    for col_offset in range(0, n_cols, BLOCK_SIZE):
        col_idx = col_offset + tl.arange(0, BLOCK_SIZE)
        mask = col_idx < n_cols

        # Load values
        vals = tl.load(row_start_ptr + col_idx, mask=mask, other=0.0)

        # Compute exp(x - max_val) and accumulate
        exp_vals = tl.exp(vals - max_val)
        sum_exp += tl.sum(tl.where(mask, exp_vals, 0.0))

    # Compute log(sum_exp)
    log_sum_exp = tl.log(sum_exp)

    # Step 3: Compute final log_softmax values: x - max_val - log_sum_exp
    for col_offset in range(0, n_cols, BLOCK_SIZE):
        col_idx = col_offset + tl.arange(0, BLOCK_SIZE)
        mask = col_idx < n_cols

        # Load values
        vals = tl.load(row_start_ptr + col_idx, mask=mask)

        # Compute log_softmax
        output = vals - max_val - log_sum_exp

        # Store results
        tl.store(output_row_start_ptr + col_idx, output, mask=mask)

@triton.jit
def _rms_norm_kernel(
    input_ptr,
    weight_ptr,
    output_ptr,
    input_row_stride,
    output_row_stride,
    n_cols,
    eps,
    BLOCK_SIZE: tl.constexpr,
):
    """
    Compute RMS normalization along the last dimension of a 2D tensor.
    RMS Norm: y = x / sqrt(mean(x^2) + eps) * weight
    Each block handles one row of the input tensor.
    """
    row_idx = tl.program_id(0).to(tl.int64)
    row_start_ptr = input_ptr + row_idx * input_row_stride
    output_row_start_ptr = output_ptr + row_idx * output_row_stride

    # Step 1: Compute sum of squares in float32 to avoid overflow
    sum_sq = tl.zeros([1], dtype=tl.float32)
    for col_offset in range(0, n_cols, BLOCK_SIZE):
        col_idx = col_offset + tl.arange(0, BLOCK_SIZE)
        mask = col_idx < n_cols

        vals = tl.load(row_start_ptr + col_idx, mask=mask, other=0.0)
        # Convert to float32 for accumulation to prevent overflow
        vals_f32 = vals.to(tl.float32)
        sq_vals = vals_f32 * vals_f32
        sum_sq += tl.sum(tl.where(mask, sq_vals, 0.0))

    # Step 2: Compute RMS (root mean square) in float32
    mean_sq = sum_sq / n_cols
    rms = tl.sqrt(mean_sq + eps)
    inv_rms = 1.0 / rms

    # Step 3: Normalize and apply weight
    for col_offset in range(0, n_cols, BLOCK_SIZE):
        col_idx = col_offset + tl.arange(0, BLOCK_SIZE)
        mask = col_idx < n_cols
        vals = tl.load(row_start_ptr + col_idx, mask=mask, other=0.0)
        weight = tl.load(weight_ptr + col_idx, mask=mask, other=1.0)
        # Compute in float32 then convert back to input dtype
        vals_f32 = vals.to(tl.float32)
        weight_f32 = weight.to(tl.float32)
        output_f32 = vals_f32 * inv_rms * weight_f32
        output = output_f32.to(vals.dtype)
        tl.store(output_row_start_ptr + col_idx, output, mask=mask)

@triton.jit
def bmm_kernel(
    a_ptr,  # (*, ) pointer to A, (B, M, K)
    b_ptr,  # (*, ) pointer to B, (B, K, N)
    c_ptr,  # (*, ) pointer to C, (B, M, N)
    B,  # int, batch size
    M,  # int, output rows
    N,  # int, output cols
    K,  # int, reduction dim
    stride_ab,
    stride_am,
    stride_ak,
    stride_bb,
    stride_bk,
    stride_bn,
    stride_cb,
    stride_cm,
    stride_cn,
    BLOCK_SIZE_M: tl.constexpr,
    BLOCK_SIZE_N: tl.constexpr,
    BLOCK_SIZE_K: tl.constexpr,
    A_LARGE: tl.constexpr,
    B_LARGE: tl.constexpr,
    C_LARGE: tl.constexpr,
):
    """Batched GEMM: (B, M, K) x (B, K, N) -> (B, M, N)

    Each program computes one (batch_idx, tile_m, tile_n) tile, accumulating
    along K in a fixed order to preserve batch invariance.
    """
    pid_b = tl.program_id(0)
    pid = tl.program_id(1)

    if pid_b >= B:
        return

    # number of tiles along M / N
    num_pid_m = tl.cdiv(M, BLOCK_SIZE_M)
    num_pid_n = tl.cdiv(N, BLOCK_SIZE_N)

    pid_m = pid // num_pid_n
    pid_n = pid % num_pid_n

    if pid_m >= num_pid_m or pid_n >= num_pid_n:
        return

    # offs_m / offs_n: raw global row/col indices for this tile
    offs_m = pid_m * BLOCK_SIZE_M + tl.arange(0, BLOCK_SIZE_M)
    offs_n = pid_n * BLOCK_SIZE_N + tl.arange(0, BLOCK_SIZE_N)
    # masks for valid logical rows/cols within (M, N)
    mask_m = offs_m < M  # [BLOCK_SIZE_M]
    mask_n = offs_n < N  # [BLOCK_SIZE_N]

    if A_LARGE or B_LARGE or C_LARGE:
        offs_m = offs_m.to(tl.int64)
        offs_n = offs_n.to(tl.int64)

    offs_m = tl.where(mask_m, offs_m, 0)
    offs_n = tl.where(mask_n, offs_n, 0)

    # hint for triton contiguous memory
    offs_m = tl.max_contiguous(tl.multiple_of(offs_m, BLOCK_SIZE_M), BLOCK_SIZE_M)
    offs_n = tl.max_contiguous(tl.multiple_of(offs_n, BLOCK_SIZE_N), BLOCK_SIZE_N)

    # base pointers for current batch, shape-wise:
    #   a_batch_ptr points to A[pid_b, 0, 0]
    #   b_batch_ptr points to B[pid_b, 0, 0]
    #   c_batch_ptr points to C[pid_b, 0, 0]
    a_batch_ptr = a_ptr + pid_b * stride_ab
    b_batch_ptr = b_ptr + pid_b * stride_bb
    c_batch_ptr = c_ptr + pid_b * stride_cb

    accumulator = tl.zeros((BLOCK_SIZE_M, BLOCK_SIZE_N), dtype=tl.float32)
    # number of K-blocks this tile iterates over
    k_tiles = tl.cdiv(K, BLOCK_SIZE_K)
    offs_k_mask = tl.arange(0, BLOCK_SIZE_K)

    for ki in range(k_tiles):
        if A_LARGE or B_LARGE:
            # offs_k: [BLOCK_SIZE_K], global K indices
            offs_k = ki * BLOCK_SIZE_K + tl.arange(0, BLOCK_SIZE_K).to(tl.int64)
        else:
            offs_k = ki * BLOCK_SIZE_K + tl.arange(0, BLOCK_SIZE_K)

        # a_ptrs: [BLOCK_SIZE_M, BLOCK_SIZE_K]
        #   element (i, j) points to A[pid_b, offs_m[i], offs_k[j]]
        a_ptrs = a_batch_ptr + (
            offs_m[:, None] * stride_am + offs_k[None, :] * stride_ak
        )
        # b_ptrs: [BLOCK_SIZE_K, BLOCK_SIZE_N]
        #   element (i, j) points to B[pid_b, offs_k[i], offs_n[j]]
        b_ptrs = b_batch_ptr + (
            offs_k[:, None] * stride_bk + offs_n[None, :] * stride_bn
        )

        # valid K lanes for this block
        k_valid = offs_k_mask < (K - ki * BLOCK_SIZE_K)
        # A mask within (M, K): [BLOCK_SIZE_M, BLOCK_SIZE_K]
        a_mask = mask_m[:, None] & k_valid[None, :]
        # B mask within (K, N): [BLOCK_SIZE_K, BLOCK_SIZE_N]
        b_mask = k_valid[:, None] & mask_n[None, :]

        # a: [BLOCK_SIZE_M, BLOCK_SIZE_K] from A[offs_m, offs_k]
        a = tl.load(
            a_ptrs,
            mask=a_mask,
            other=0.0,
        )
        # b: [BLOCK_SIZE_K, BLOCK_SIZE_N] from B[offs_k, offs_n]
        b = tl.load(
            b_ptrs,
            mask=b_mask,
            other=0.0,
        )
        accumulator = tl.dot(a, b, accumulator)

    # c_m / c_n: [BLOCK_SIZE_M] / [BLOCK_SIZE_N], row/col indices for C
    c_m = offs_m
    c_n = offs_n
    if C_LARGE:
        c_m = c_m.to(tl.int64)
        c_n = c_n.to(tl.int64)

    # c_ptrs: [BLOCK_SIZE_M, BLOCK_SIZE_N]
    #   element (i, j) points to C[pid_b, c_m[i], c_n[j]]
    c_ptrs = c_batch_ptr + stride_cm * c_m[:, None] + stride_cn * c_n[None, :]
    # mask out elements that fall outside logical (M, N) range
    c_mask = mask_m[:, None] & mask_n[None, :]
    # cast FP32 accumulator back to original dtype of C
    c = accumulator.to(c_ptr.dtype.element_ty)
    tl.store(c_ptrs, c, mask=c_mask)

def log_softmax(input: torch.Tensor, dim: int = -1) -> torch.Tensor:
    """
    Compute log_softmax using Triton kernel.

    Args:
        input: Input tensor
        dim: Dimension along which to compute log_softmax
             (only -1 or last dim supported)
    >> Stashed changes
    Returns:
        Tensor with log_softmax applied along the specified dimension
    """
    if dim != -1 and dim != input.ndim - 1:
        raise ValueError(
            "This implementation only supports log_softmax along the last dimension"
        )

    # Flatten all dimensions except the last one
    original_shape = input.shape
    input_2d = input.reshape(-1, input.shape[-1])
    input_2d = input_2d.contiguous()

    n_rows, n_cols = input_2d.shape

    # Allocate output tensor
    output = torch.empty_like(input_2d)

    # Choose block size based on the number of columns
    BLOCK_SIZE = 1024

    # Launch kernel with one block per row
    grid = (n_rows,)
    _log_softmax_kernel[grid](
        input_2d,
        output,
        input_2d.stride(0),
        output.stride(0),
        n_cols,
        BLOCK_SIZE=BLOCK_SIZE,
    )
    # Reshape output back to original shape
    return output.reshape(original_shape)

def mean_dim(
    input: torch.Tensor,
    dim: int,
    keepdim: bool = False,
    dtype: torch.dtype | None = None,
) -> torch.Tensor:
    """
    Triton implementation of torch.mean with single dimension reduction.

    Args:
        input: Input tensor
        dim: Single dimension along which to compute mean
        keepdim: Whether to keep the reduced dimension
        dtype: Output dtype. If None, uses input dtype
               (or float32 for integer inputs)

    Returns:
        Tensor with mean values along specified dimension
    """
    # Validate inputs
    assert -input.ndim <= dim < input.ndim, (
        f"Invalid dimension {dim} for tensor with {input.ndim} dimensions"
    )

    # Handle negative dim
    if dim < 0:
        dim = dim + input.ndim

    # Handle dtype
    if dtype is None:
        if input.dtype in [torch.int8, torch.int16, torch.int32, torch.int64]:
            dtype = torch.float32
        else:
            dtype = input.dtype

    # Convert input to appropriate dtype if needed
    if input.dtype != dtype:
        input = input.to(dtype)

    # Get input shape and strides
    shape = list(input.shape)

    # Calculate dimensions for kernel
    M = 1
    for i in range(dim):
        M *= shape[i]

    N = shape[dim]

    K = 1
    for i in range(dim + 1, len(shape)):
        K *= shape[i]

    # Reshape input to 3D view (M, N, K)
    input_3d = input.reshape(M, N, K)

    # Create output shape
    if keepdim:
        output_shape = shape.copy()
        output_shape[dim] = 1
    else:
        output_shape = shape[:dim] + shape[dim + 1 :]

    # Create output tensor
    output = torch.empty(output_shape, dtype=dtype, device=input.device)

    # Reshape output for kernel
    output_2d = output.reshape(M, 1, K).squeeze(1) if keepdim else output.reshape(M, K)

    # Launch kernel
    grid = (M * K,)
    BLOCK_SIZE = 1024

    mean_kernel[grid](
        input_3d,
        output_2d,
        input_3d.stride(0),
        input_3d.stride(1),
        input_3d.stride(2),
        output_2d.stride(0),
        output_2d.stride(1) if output_2d.ndim > 1 else 0,
        M,
        N,
        K,
        BLOCK_SIZE,
    )

    return output

@triton.jit
def mean_kernel(
    input_ptr,
    output_ptr,
    input_stride0,
    input_stride1,
    input_stride2,
    output_stride0,
    output_stride1,
    M,  # size before reduction dim
    N,  # size of reduction dim
    K,  # size after reduction dim
    BLOCK_SIZE: tl.constexpr,
):
    """
    Kernel for computing mean along a single dimension.
    Input is viewed as (M, N, K) where N is the dimension being reduced.
    """
    # Program ID gives us which output element we're computing
    pid = tl.program_id(0)

    # Compute output indices
    m_idx = pid // K
    k_idx = pid % K

    # Bounds check
    if m_idx >= M or k_idx >= K:
        return

    # Accumulate sum across reduction dimension
    acc = 0.0
    for n_start in range(0, N, BLOCK_SIZE):
        n_offsets = n_start + tl.arange(0, BLOCK_SIZE)
        mask = n_offsets < N

        # Calculate input indices
        input_idx = (
            m_idx * input_stride0 + n_offsets * input_stride1 + k_idx * input_stride2
        )

        # Load and accumulate
        vals = tl.load(input_ptr + input_idx, mask=mask, other=0.0)
        acc += tl.sum(vals)

    # Compute mean and store
    mean_val = acc / N
    output_idx = m_idx * output_stride0 + k_idx * output_stride1
    tl.store(output_ptr + output_idx, mean_val)

def rms_norm(
    input: torch.Tensor, weight: torch.Tensor, eps: float = 1e-6
) -> torch.Tensor:
    """
    Compute RMS normalization using Triton kernel.

    RMS Norm normalizes the input by the root mean square and scales by weight:
    output = input / sqrt(mean(input^2) + eps) * weight

    Args:
        input: Input tensor of shape (..., hidden_size)
        weight: Weight tensor of shape (hidden_size,)
        eps: Small constant for numerical stability

    Returns:
        Tensor with RMS normalization applied along the last dimension
    """
    assert weight.dim() == 1, "Weight must be 1-dimensional"
    assert input.shape[-1] == weight.shape[0], (
        f"Input last dimension ({input.shape[-1]}) must match "
        f"weight dimension ({weight.shape[0]})"
    )

    # Flatten all dimensions except the last one
    original_shape = input.shape
    input_2d = input.reshape(-1, input.shape[-1])
    input_2d = input_2d.contiguous()
    weight = weight.contiguous()

    n_rows, n_cols = input_2d.shape

    output = torch.empty_like(input_2d)
    BLOCK_SIZE = 1024
    grid = (n_rows,)
    _rms_norm_kernel[grid](
        input_2d,
        weight,
        output,
        input_2d.stride(0),
        output.stride(0),
        n_cols,
        eps,
        BLOCK_SIZE=BLOCK_SIZE,
    )
    return output.reshape(original_shape)

def rms_norm_batch_invariant(
    input: torch.Tensor, weight: torch.Tensor, eps: float = 1e-6
) -> torch.Tensor:
    """
    Batch-invariant wrapper for RMS normalization.

    This function provides a deterministic, batch-invariant implementation
    of RMS normalization for use with the batch_invariant mode.

    Args:
        input: Input tensor of shape (..., hidden_size)
        weight: Weight tensor of shape (hidden_size,)
        eps: Small constant for numerical stability

    Returns:
        RMS normalized tensor
    """
    return rms_norm(input, weight, eps=eps)