vllm.utils.deep_gemm ¶

def _import_deep_gemm():
    """Import the deep_gemm module.

    Prefers an externally installed ``deep_gemm`` package (so users can
    pin a specific version), then falls back to the vendored copy bundled
    in the vLLM wheel.

    Returns ``None`` when neither source is usable.
    """
    # 1. Try the external (pip-installed) package first.
    try:
        module = importlib.import_module("deep_gemm")
        logger.debug_once("Imported deep_gemm module from site-packages")
        return module
    except ImportError:
        logger.debug_once(
            "deep_gemm not found in site-packages, "
            "trying vendored vllm.third_party.deep_gemm"
        )

    # 2. Fall back to the vendored copy bundled in the vLLM wheel.
    try:
        module = importlib.import_module("vllm.third_party.deep_gemm")
        logger.debug_once("Imported deep_gemm module from vllm.third_party.deep_gemm")
        return module
    except ImportError:
        logger.debug_once("Vendored deep_gemm not found either")
    except Exception as e:
        # The vendored module may raise RuntimeError during _C.init()
        # if JIT include files are missing (e.g. incomplete wheel).
        logger.warning_once("Failed to import vendored deep_gemm: %s", e)

    return None

def _lazy_init() -> None:
    """Import deep_gemm and resolve symbols on first use."""
    global _cublaslt_gemm_nt_impl
    global _fp8_gemm_nt_impl, _fp8_einsum_impl
    global _grouped_impl, _grouped_masked_impl, _grouped_fp4_impl
    global _fp8_fp4_mqa_logits_impl, _fp8_fp4_paged_mqa_logits_impl
    global _get_paged_mqa_logits_metadata_impl
    global _tf32_hc_prenorm_gemm_impl
    global _get_mn_major_tma_aligned_tensor_impl
    global _get_mk_alignment_for_contiguous_layout_impl
    global _transform_sf_into_required_layout_impl
    # fast path
    if (
        _cublaslt_gemm_nt_impl is not None
        or _fp8_gemm_nt_impl is not None
        or _fp8_einsum_impl is not None
        or _grouped_impl is not None
        or _grouped_masked_impl is not None
        or _grouped_fp4_impl is not None
        or _fp8_fp4_mqa_logits_impl is not None
        or _fp8_fp4_paged_mqa_logits_impl is not None
        or _get_paged_mqa_logits_metadata_impl is not None
        or _tf32_hc_prenorm_gemm_impl is not None
        or _get_mk_alignment_for_contiguous_layout_impl is not None
        or _transform_sf_into_required_layout_impl is not None
    ):
        return

    if not has_deep_gemm():
        return

    # Set up deep_gemm cache path
    DEEP_GEMM_JIT_CACHE_ENV_NAME = "DG_JIT_CACHE_DIR"
    if not os.environ.get(DEEP_GEMM_JIT_CACHE_ENV_NAME, None):
        os.environ[DEEP_GEMM_JIT_CACHE_ENV_NAME] = os.path.join(
            envs.VLLM_CACHE_ROOT, "deep_gemm"
        )

    _dg = _import_deep_gemm()
    if _dg is None:
        return

    _cublaslt_gemm_nt_impl = getattr(_dg, "cublaslt_gemm_nt", None)
    _fp8_gemm_nt_impl = getattr(_dg, "fp8_gemm_nt", None)
    _fp8_einsum_impl = getattr(_dg, "fp8_einsum", None)
    _grouped_impl = getattr(_dg, "m_grouped_fp8_gemm_nt_contiguous", None)
    _grouped_masked_impl = getattr(_dg, "fp8_m_grouped_gemm_nt_masked", None)
    _grouped_fp4_impl = getattr(_dg, "m_grouped_fp8_fp4_gemm_nt_contiguous", None)
    # DeepGEMM exposes fp8_fp4_*_mqa_logits as the canonical symbols that
    # handle both the FP8 and FP4 Q/K paths via a tuple-typed `q`.
    _fp8_fp4_mqa_logits_impl = getattr(_dg, "fp8_fp4_mqa_logits", None)
    _fp8_fp4_paged_mqa_logits_impl = getattr(_dg, "fp8_fp4_paged_mqa_logits", None)
    _get_paged_mqa_logits_metadata_impl = getattr(
        _dg, "get_paged_mqa_logits_metadata", None
    )
    _tf32_hc_prenorm_gemm_impl = getattr(_dg, "tf32_hc_prenorm_gemm", None)
    _get_mn_major_tma_aligned_tensor_impl = getattr(
        _dg, "get_mn_major_tma_aligned_tensor", None
    )
    _get_mk_alignment_for_contiguous_layout_impl = getattr(
        _dg, "get_mk_alignment_for_contiguous_layout", None
    )
    _transform_sf_into_required_layout_impl = getattr(
        _dg, "transform_sf_into_required_layout", None
    )
    DeepGemmQuantScaleFMT.init_oracle_cache()

def _missing(*_: Any, **__: Any) -> NoReturn:
    """Placeholder for unavailable DeepGEMM backend."""
    raise RuntimeError(
        "DeepGEMM backend is not available or outdated. Please install or "
        "update the `deep_gemm` to a newer version to enable FP8 kernels."
    )

def calc_diff(x: torch.Tensor, y: torch.Tensor):
    """Return a global difference metric for unit tests.

    DeepGEMM kernels on Blackwell/B200 currently exhibit noticeable per-element
    error, causing `torch.testing.assert_close` to fail.  Instead of checking
    every element, we compute a cosine-style similarity over the whole tensor
    and report `1 - sim`.  Once kernel accuracy improves this helper can be
    removed.
    """

    x, y = x.double(), y.double()
    denominator = (x * x + y * y).sum()
    sim = 2 * (x * y).sum() / denominator
    return 1 - sim

def fp8_fp4_mqa_logits(
    q: tuple[torch.Tensor, torch.Tensor | None],
    kv: tuple[torch.Tensor, torch.Tensor],
    weights: torch.Tensor,
    cu_seqlen_ks: torch.Tensor,
    cu_seqlen_ke: torch.Tensor,
    clean_logits: bool,
) -> torch.Tensor:
    """Compute MQA logits for a single sequence without KV paging.

    Unified FP8/FP4 dispatch — the underlying DeepGEMM kernel takes
    ``q = (values, scales_or_None)`` where ``scales`` is None for FP8 Q
    (per-token scale is folded into ``weights``) and a packed block-scale
    tensor for MXFP4 Q.

    Args:
        q: Tuple ``(q_values, q_scale)``. FP8 path: q_values is [M, H, D]
            float8_e4m3fn and q_scale is None (per-token scale is folded
            into ``weights``). FP4 path: q_values is packed uint8 and
            q_scale is the companion block-scale tensor.
        kv: Tuple `(k_packed, k_scales)` — FP8 layout is [N, D]
            float8_e4m3fn plus fp32 scales [N]; FP4 layout is packed uint8.
        weights: weights of shape [M, H], dtype `torch.float32`.
        cu_seqlen_ks: Start indices (inclusive) for valid K per query
            position, shape [M], dtype int32.
        cu_seqlen_ke: End indices (exclusive) for valid K per query
            position, shape [M], dtype int32.
        clean_logits: Whether to clean the unfilled logits into `-inf`.

    Returns:
        Logits tensor of shape [M, N], dtype `torch.float32`.
    """
    _lazy_init()
    if _fp8_fp4_mqa_logits_impl is None:
        return _missing()
    return _fp8_fp4_mqa_logits_impl(
        q,
        kv,
        weights,
        cu_seqlen_ks,
        cu_seqlen_ke,
        clean_logits=clean_logits,
    )

def fp8_fp4_paged_mqa_logits(
    q: tuple[torch.Tensor, torch.Tensor | None],
    kv_cache: torch.Tensor,
    weights: torch.Tensor,
    context_lens: torch.Tensor,
    block_tables: torch.Tensor,
    schedule_metadata: torch.Tensor,
    max_model_len: int,
    clean_logits: bool,
) -> torch.Tensor:
    """Compute MQA logits using a paged KV-cache.

    Unified FP8/FP4 dispatch — the underlying DeepGEMM kernel takes
    ``q = (values, scales_or_None)``; pass ``(q_tensor, None)`` for the FP8
    path and ``(q_values, q_scale)`` for MXFP4.

    Args:
        q: Tuple ``(q_values, q_scale)``. FP8 path: q_values is
            [B, next_n, H, D] float8_e4m3fn and q_scale is None. FP4 path:
            q_values is packed uint8 and q_scale is the companion
            block-scale tensor.
        kv_cache: Paged KV-cache. FP8 layout is [num_blocks, block_size, 1,
            D+4], dtype `torch.uint8`, with the last 4 bytes per (block, pos)
            storing the float dequant scale.
        weights: Tensor of shape [B * next_n, H], dtype `torch.float32`.
        context_lens: Tensor of shape [B], dtype int32; effective context length
            for each batch element.
        block_tables: Tensor of shape [B, max_blocks], dtype int32; maps logical
            block indices to physical blocks in the paged cache.
        schedule_metadata: Returned by `get_paged_mqa_logits_metadata`;
            used to distribute work across SMs.
        max_model_len: Maximum sequence length used to size the logits output.
        clean_logits: Whether to clean the unfilled logits into `-inf`.

    Returns:
        Logits tensor of shape [B * next_n, max_model_len], dtype
        `torch.float32`.
    """
    _lazy_init()
    if _fp8_fp4_paged_mqa_logits_impl is None:
        return _missing()
    return _fp8_fp4_paged_mqa_logits_impl(
        q,
        kv_cache,
        weights,
        context_lens,
        block_tables,
        schedule_metadata,
        max_model_len,
        clean_logits=clean_logits,
    )

def get_col_major_tma_aligned_tensor(x: torch.Tensor) -> torch.Tensor:
    """Wrapper for DeepGEMM's get_mn_major_tma_aligned_tensor"""
    _lazy_init()
    if _get_mn_major_tma_aligned_tensor_impl is None:
        return _missing()
    return _get_mn_major_tma_aligned_tensor_impl(x)

def get_paged_mqa_logits_metadata(
    context_lens: torch.Tensor, block_size: int, num_sms: int
) -> torch.Tensor:
    """Build scheduling metadata for paged MQA logits.

    Args:
        context_lens: Tensor of shape [B], dtype int32; effective context length
            per batch element.
        block_size: KV-cache block size in tokens (e.g., 64).
        num_sms: Number of SMs available. 132 for Hopper

    Returns:
        Backend-specific tensor consumed by `fp8_fp4_paged_mqa_logits` to
        schedule work across SMs.
    """
    _lazy_init()
    if _get_paged_mqa_logits_metadata_impl is None:
        return _missing()
    return _get_paged_mqa_logits_metadata_impl(context_lens, block_size, num_sms)

@functools.cache
def is_deep_gemm_e8m0_used() -> bool:
    """Return `True` if vLLM is configured to use DeepGEMM "
    "E8M0 scale on a Hopper or Blackwell-class GPU.
    """
    if not is_deep_gemm_supported():
        logger.debug_once(
            "DeepGEMM E8M0 disabled: DeepGEMM not supported on this system."
        )
        return False

    _lazy_init()

    if _fp8_gemm_nt_impl is None:
        logger.info_once("DeepGEMM E8M0 disabled: _fp8_gemm_nt_impl not found")
        return False

    if envs.VLLM_USE_DEEP_GEMM_E8M0:
        logger.info_once("DeepGEMM E8M0 enabled on current platform.")
        return True

    logger.info_once("DeepGEMM E8M0 disabled on current configuration.")
    return False

@functools.cache
def is_deep_gemm_supported() -> bool:
    """Return `True` if DeepGEMM is supported on the current platform.
    Currently, only Hopper and Blackwell GPUs are supported.
    """
    is_supported_arch = current_platform.support_deep_gemm()
    return envs.VLLM_USE_DEEP_GEMM and has_deep_gemm() and is_supported_arch

def should_auto_disable_deep_gemm(model_type: str | None) -> bool:
    """Check if DeepGemm should be auto-disabled for this model on Blackwell.

    Returns True if the model is known to have accuracy degradation with
    DeepGemm's E8M0 scale format on Blackwell GPUs (SM100+).
    """
    if model_type is None:
        return False
    if not current_platform.is_device_capability_family(100):
        return False
    return model_type in _DEEPGEMM_BLACKWELL_EXCLUDED_MODEL_TYPES

def tf32_hc_prenorm_gemm(
    x: torch.Tensor,
    fn: torch.Tensor,
    out: torch.Tensor,
    sqrsum: torch.Tensor,
    num_split: int,
) -> torch.Tensor:
    """
    Perform the following computation:
        out = x.float() @ fn.T
        sqrsum = x.float().square().sum(-1)

    See the caller function for shape requirement
    """
    _lazy_init()
    if _tf32_hc_prenorm_gemm_impl is None:
        return _missing()
    return _tf32_hc_prenorm_gemm_impl(
        x,
        fn,
        out,
        sqrsum,
        num_split,
    )