vllm.distributed.kv_transfer.kv_connector.v1.ssm_conv_transfer_utils ¶

def compute_physical_blocks_per_logical(
    ssm_sizes: tuple[int, ...], block_len: int
) -> int:
    """Derive _physical_blocks_per_logical_kv_block from remote metadata.

    The remote engine's ratio is not sent directly in the handshake, so we
    reconstruct it: total mamba state per logical block / block_len.

    Args:
        ssm_sizes: (conv_state_bytes, ssm_state_bytes) from NixlAgentMetadata.
        block_len: the engine's block_len in bytes (from block_lens[0]).
    """
    return math.ceil((ssm_sizes[0] + ssm_sizes[1]) / block_len)

def derive_mamba_conv_split(
    mamba_spec: MambaSpec,
    local_tp: int,
) -> MambaConvSplitInfo:
    """Derive per-rank sub-projection byte sizes from a MambaSpec.

    Called once at init on both P and D.  Decomposes the conv dimension
    into its sub-projection parts based on the model type.

    Args:
        mamba_spec: MambaSpec whose shapes are:
            shapes[0] = conv state: (conv_dim_local, conv_rows) in DS layout.
            shapes[1] = temporal state (model-specific shape).
        local_tp: this engine's tensor-parallel size.

    Returns:
        MambaConvSplitInfo with per-rank sub-projection dims, conv_rows,
        conv_dtype_size, and ssm_sizes (conv_state_bytes, ssm_state_bytes).
    """
    _supported = (
        MambaAttentionBackendEnum.MAMBA2,
        MambaAttentionBackendEnum.GDN_ATTN,
    )
    if mamba_spec.mamba_type not in _supported:
        raise NotImplementedError(
            f"3-read conv transfer only supports Mamba2 and GDN models, "
            f"got mamba_type={mamba_spec.mamba_type!r}."
        )

    conv_shape = mamba_spec.shapes[0]
    assert len(conv_shape) == 2, f"Expected 2D conv state shape, got {conv_shape}"

    # NOTE (ZhanqiuHu): 3-read requires DS layout, which is already asserted
    # in nixl worker __init__.  Use it directly instead of heuristic detection.
    assert is_conv_state_dim_first(), "3-read requires DS conv state layout"
    local_conv_dim = conv_shape[0]  # DS: (conv_dim_local, conv_rows)
    conv_rows = conv_shape[1]

    conv_dtype_size = torch.tensor(
        [],
        dtype=mamba_spec.dtypes[0],  # type: ignore[misc]
    ).element_size()
    ssm_dtype_size = torch.tensor(
        [],
        dtype=mamba_spec.dtypes[1],  # type: ignore[misc]
    ).element_size()
    conv_state_bytes = torch.Size(mamba_spec.shapes[0]).numel() * conv_dtype_size
    ssm_state_bytes = torch.Size(mamba_spec.shapes[1]).numel() * ssm_dtype_size

    if mamba_spec.mamba_type == MambaAttentionBackendEnum.MAMBA2:
        # NOTE (ZhanqiuHu): intermediate_size (= global x dim) is not stored
        # in MambaSpec, so we reconstruct it from the SSM temporal state shape:
        #   shapes[1] = (local_num_heads, head_dim), already divided by TP.
        head_dim = mamba_spec.shapes[1][1]
        local_num_heads = mamba_spec.shapes[1][0]
        intermediate_size = local_num_heads * local_tp * head_dim

        # NOTE (ZhanqiuHu): global conv dim = intermediate_size + 2 * groups_ss,
        # where groups_ss is the B (= C) dimension.  B and C are always the same
        # size, so we recover groups_ss from the remainder after subtracting x.
        remainder = local_conv_dim * local_tp - intermediate_size
        assert remainder > 0 and remainder % 2 == 0, (
            f"Conv dim ({local_conv_dim}*tp={local_tp}) doesn't decompose "
            f"into intermediate_size={intermediate_size} + 2*groups_ss. "
            f"remainder={remainder}"
        )
        groups_ss = remainder // 2

        # Divide by TP to get per-rank column counts.
        x_local = intermediate_size // local_tp
        b_local = groups_ss // local_tp
        local_proj_dims = (x_local, b_local, b_local)
    elif mamba_spec.mamba_type == MambaAttentionBackendEnum.GDN_ATTN:
        # GDN: conv = [Q, K, V] where dim(Q) == dim(K) == key_dim.
        # conv_dim = key_dim*2 + value_dim (all global, divided by TP).
        # Temporal state shape is (num_v_heads/TP, head_v_dim, head_k_dim).
        temporal_shape = mamba_spec.shapes[1]
        num_v_heads_local = temporal_shape[0]
        head_v_dim = temporal_shape[1]
        value_dim_local = num_v_heads_local * head_v_dim

        remainder = local_conv_dim - value_dim_local
        assert remainder > 0 and remainder % 2 == 0, (
            f"GDN conv dim ({local_conv_dim}) doesn't decompose into "
            f"2*key_dim_local + value_dim_local={value_dim_local}. "
            f"remainder={remainder}"
        )
        key_dim_local = remainder // 2
        local_proj_dims = (key_dim_local, key_dim_local, value_dim_local)
    else:
        raise NotImplementedError(
            f"Conv split not supported for mamba_type={mamba_spec.mamba_type!r}"
        )

    return MambaConvSplitInfo(
        conv_rows=conv_rows,
        local_proj_dims=local_proj_dims,
        conv_dtype_size=conv_dtype_size,
        ssm_sizes=(conv_state_bytes, ssm_state_bytes),
    )