selector.py

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

from functools import cache
from typing import NamedTuple, cast, get_args

import torch

from vllm.config.cache import CacheDType
from vllm.logger import init_logger
from vllm.utils.import_utils import resolve_obj_by_qualname
from vllm.v1.attention.backend import AttentionBackend, AttentionType
from vllm.v1.attention.backends.registry import (
    MAMBA_TYPE_TO_BACKEND_MAP,
    MambaAttentionBackendEnum,
)

logger = init_logger(__name__)


class AttentionSelectorConfig(NamedTuple):
    head_size: int
    dtype: torch.dtype
    kv_cache_dtype: CacheDType | None
    block_size: int | None
    use_mla: bool = False
    has_sink: bool = False
    use_sparse: bool = False
    use_mm_prefix: bool = False
    use_alibi_sqrt: bool = False
    attn_type: str = AttentionType.DECODER

    def __repr__(self):
        return (
            f"AttentionSelectorConfig(head_size={self.head_size}, "
            f"dtype={self.dtype}, "
            f"kv_cache_dtype={self.kv_cache_dtype}, "
            f"block_size={self.block_size}, "
            f"use_mla={self.use_mla}, "
            f"has_sink={self.has_sink}, "
            f"use_sparse={self.use_sparse}, "
            f"use_mm_prefix={self.use_mm_prefix}, "
            f"use_alibi_sqrt={self.use_alibi_sqrt}, "
            f"attn_type={self.attn_type})"
        )


def get_attn_backend(
    head_size: int,
    dtype: torch.dtype,
    kv_cache_dtype: str | None,
    block_size: int | None,
    use_mla: bool = False,
    has_sink: bool = False,
    use_sparse: bool = False,
    use_mm_prefix: bool = False,
    use_alibi_sqrt: bool = False,
    attn_type: str | None = None,
) -> type[AttentionBackend]:
    """Selects which attention backend to use and lazily imports it."""

    if kv_cache_dtype is not None:
        valid_cache_dtypes = get_args(CacheDType)
        assert kv_cache_dtype in valid_cache_dtypes, (
            f"Invalid kv_cache_dtype: {kv_cache_dtype}. "
            f"Valid values are: {valid_cache_dtypes}"
        )

    from vllm.config import get_current_vllm_config

    vllm_config = get_current_vllm_config()
    backend_enum = vllm_config.attention_config.backend

    attn_selector_config = AttentionSelectorConfig(
        head_size=head_size,
        dtype=dtype,
        kv_cache_dtype=cast(CacheDType | None, kv_cache_dtype),
        block_size=block_size,
        use_mla=use_mla,
        has_sink=has_sink,
        use_sparse=use_sparse,
        use_mm_prefix=use_mm_prefix,
        use_alibi_sqrt=use_alibi_sqrt,
        attn_type=attn_type or AttentionType.DECODER,
    )

    return _cached_get_attn_backend(
        backend=backend_enum,
        attn_selector_config=attn_selector_config,
    )


@cache
def _cached_get_attn_backend(
    backend,
    attn_selector_config: AttentionSelectorConfig,
) -> type[AttentionBackend]:
    from vllm.platforms import current_platform

    attention_cls = current_platform.get_attn_backend_cls(
        backend,
        attn_selector_config=attn_selector_config,
    )
    if not attention_cls:
        raise ValueError(
            f"Invalid attention backend for {current_platform.device_name}"
        )
    backend = resolve_obj_by_qualname(attention_cls)

    # Adjust kv cache layout if the selected backend requires a specific one
    required_layout = backend.get_required_kv_cache_layout()
    if required_layout is not None:
        from vllm.v1.attention.backends.utils import set_kv_cache_layout

        set_kv_cache_layout(required_layout)
        logger.info(
            "Using %s KV cache layout for %s backend.",
            required_layout,
            backend.get_name(),
        )

    return backend


def get_mamba_attn_backend(
    mamba_type: str,
) -> type[AttentionBackend]:
    """Select which mamba attention backend to use and lazily import it."""
    return _cached_get_mamba_attn_backend(mamba_type)


@cache
def _cached_get_mamba_attn_backend(
    mamba_type: str,
) -> type[AttentionBackend]:
    assert mamba_type and isinstance(mamba_type, str)

    selected_backend = None
    try:
        backend_name = MAMBA_TYPE_TO_BACKEND_MAP[mamba_type]
        selected_backend = MambaAttentionBackendEnum[backend_name]
    except KeyError as e:
        raise ValueError(
            f"Invalid mamba attention backend type: '{backend_name}'. Valid "
            f"backends are: {list(MambaAttentionBackendEnum.__members__.keys())}"
        ) from e

    mamba_attn_backend = selected_backend.get_class()
    return mamba_attn_backend