vllm.model_executor.layers.sparse_attn_indexer ¶

@CustomOp.register("sparse_attn_indexer")
class SparseAttnIndexer(CustomOp):
    """Sparse Attention Indexer Custom Op Layer. This layer is extracted as a
    separate custom op since it involves heavy custom kernels like `mqa_logits`,
    `paged_mqa_logits` and `top_k_per_row`, etc. Those kernels maybe requires
    specific memory layout or implementation for different hardware backends to
    achieve optimal performance.

    For now, the default native path will use CUDA backend path. Other platform
    may requires add the corresponding Custom Op name `sparse_attn_indexer` to
    `custom_ops` in `CompilationConfig` to enable the platform specific path.
    """

    def __init__(
        self,
        k_cache,
        quant_block_size: int,
        scale_fmt: str,
        topk_tokens: int,
        head_dim: int,
        max_model_len: int,
        max_total_seq_len: int,
        topk_indices_buffer: torch.Tensor,
        skip_k_cache_insert: bool = False,
        use_fp4_cache: bool = False,
    ):
        super().__init__()
        self.k_cache = k_cache
        self.quant_block_size = quant_block_size
        self.scale_fmt = scale_fmt
        self.topk_tokens = topk_tokens
        self.head_dim = head_dim
        self.max_model_len = max_model_len
        self.max_total_seq_len = max_total_seq_len
        self.topk_indices_buffer = topk_indices_buffer
        self.skip_k_cache_insert = skip_k_cache_insert
        self.use_fp4_cache = use_fp4_cache
        if current_platform.is_cuda() and not has_deep_gemm():
            raise RuntimeError(
                "Sparse Attention Indexer CUDA op requires DeepGEMM support in "
                "the current vLLM environment."
            )

    def forward_native(
        self,
        hidden_states: torch.Tensor,
        q_quant: torch.Tensor | tuple[torch.Tensor, torch.Tensor],
        k: torch.Tensor,
        weights: torch.Tensor,
    ):
        if current_platform.is_cuda() or current_platform.is_xpu():
            return self.forward_cuda(hidden_states, q_quant, k, weights)
        elif current_platform.is_rocm():
            return self.forward_hip(hidden_states, q_quant, k, weights)
        else:
            raise NotImplementedError(
                "SparseAttnIndexer native forward is only implemented for "
                "CUDA, ROCm and XPU platforms."
            )

    def forward_cuda(
        self,
        hidden_states: torch.Tensor,
        q_quant: torch.Tensor | tuple[torch.Tensor, torch.Tensor],
        k: torch.Tensor,
        weights: torch.Tensor,
    ):
        # FP8 path: single tensor (per-token scale is folded into `weights`).
        # FP4 path: (values, scales) tuple with scales required by the kernel.
        if isinstance(q_quant, tuple):
            q_values, q_scale = q_quant
        else:
            q_values, q_scale = q_quant, None
        return torch.ops.vllm.sparse_attn_indexer(
            hidden_states,
            _encode_layer_name(self.k_cache.prefix),
            self.k_cache.kv_cache,
            q_values,
            q_scale,
            k,
            weights,
            self.quant_block_size,
            self.scale_fmt,
            self.topk_tokens,
            self.head_dim,
            self.max_model_len,
            self.max_total_seq_len,
            self.topk_indices_buffer,
            self.skip_k_cache_insert,
            self.use_fp4_cache,
        )

    def forward_xpu(
        self,
        hidden_states: torch.Tensor,
        q_fp8: torch.Tensor,
        k: torch.Tensor,
        weights: torch.Tensor,
    ):
        return self.forward_cuda(hidden_states, q_fp8, k, weights)

    def forward_hip(
        self,
        hidden_states: torch.Tensor,
        q_quant: torch.Tensor | tuple[torch.Tensor, torch.Tensor],
        k: torch.Tensor,
        weights: torch.Tensor,
    ):
        assert not self.use_fp4_cache, "AMD platform doesn't support fp4 cache yet"
        assert isinstance(q_quant, torch.Tensor), (
            "AMD sparse_attn_indexer expects a single FP8 q_quant tensor"
        )
        if rocm_aiter_ops.is_enabled():
            return torch.ops.vllm.rocm_aiter_sparse_attn_indexer(
                hidden_states,
                _encode_layer_name(self.k_cache.prefix),
                self.k_cache.kv_cache,
                q_quant,
                k,
                weights,
                self.quant_block_size,
                self.scale_fmt,
                self.topk_tokens,
                self.head_dim,
                self.max_model_len,
                self.max_total_seq_len,
                self.topk_indices_buffer,
                skip_k_cache_insert=self.skip_k_cache_insert,
            )
        raise RuntimeError(
            "Sparse attention indexer ROCm path is only supported on AITER. "
            "Please enable aiter with VLLM_ROCM_USE_AITER=1"
        )