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vllm.models.minimax_m3.amd.sparse_attention_nvfp4

MiniMax M3 block-sparse attention over an NVFP4 K/V cache on ROCm (gfx950).

The cache spec is NVIDIA's, but the bytes inside a page are laid out for the FlyDSL kernels, so pages are not interchangeable with NVIDIA's.

Classes:

Functions:

MiniMaxM3SparseRocmNvfp4Backend

Bases: MiniMaxM3SparseBackend

MiniMax M3 sparse attend over NVFP4 K/V pages (ROCm, gfx950).

Methods:

  • customize_spec –

    Store each head's K and V as two slots of packed data + block scales.

Source code in vllm/models/minimax_m3/amd/sparse_attention_nvfp4.py 
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class MiniMaxM3SparseRocmNvfp4Backend(MiniMaxM3SparseBackend):
    """MiniMax M3 sparse attend over NVFP4 K/V pages (ROCm, gfx950)."""

    supported_kv_cache_dtypes: ClassVar[list[CacheDType]] = ["nvfp4"]

    @staticmethod
    def get_builder_cls() -> type["MiniMaxM3SparseRocmNvfp4MetadataBuilder"]:
        return MiniMaxM3SparseRocmNvfp4MetadataBuilder

    @classmethod
    def customize_spec(cls, spec: AttentionSpec) -> AttentionSpec:
        """Store each head's K and V as two slots of packed data + block scales."""
        if spec.state_content_bytes is not None or not spec.kv_quant_mode.is_nvfp4:
            return spec
        return replace(
            spec,
            num_head_slots=2 * spec.num_kv_heads,
            state_content_bytes=nvfp4_kv_cache_full_dim(spec.head_size)
            * get_dtype_size(spec.dtype),
        )

    @classmethod
    def supported_kv_cache_layouts(cls) -> tuple[KVCacheLayout, ...] | None:
        # The kernels read the page stride from stride(0) and address pages in
        # 64 bits, so block-outer packing works too (opt in with BLHNC).
        return (KVCacheLayout.LBHNC, KVCacheLayout.BLHNC)

customize_spec(spec) classmethod

Store each head's K and V as two slots of packed data + block scales.

Source code in vllm/models/minimax_m3/amd/sparse_attention_nvfp4.py 
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@classmethod
def customize_spec(cls, spec: AttentionSpec) -> AttentionSpec:
    """Store each head's K and V as two slots of packed data + block scales."""
    if spec.state_content_bytes is not None or not spec.kv_quant_mode.is_nvfp4:
        return spec
    return replace(
        spec,
        num_head_slots=2 * spec.num_kv_heads,
        state_content_bytes=nvfp4_kv_cache_full_dim(spec.head_size)
        * get_dtype_size(spec.dtype),
    )

MiniMaxM3SparseRocmNvfp4Impl

Bases: MiniMaxM3SparseImpl

FlyDSL NVFP4 sparse decode (bf16 compute) and prefill (fp16 compute).

Source code in vllm/models/minimax_m3/amd/sparse_attention_nvfp4.py 
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class MiniMaxM3SparseRocmNvfp4Impl(MiniMaxM3SparseImpl):
    """FlyDSL NVFP4 sparse decode (bf16 compute) and prefill (fp16 compute)."""

    def __init__(self, *args, **kwargs) -> None:
        super().__init__(*args, **kwargs)
        reason = rocm_nvfp4_unsupported_reason(
            self.num_heads,
            self.num_kv_heads,
            self.head_size,
            self.topk_blocks,
            self.block_size,
        )
        if reason is not None:
            raise ValueError(f"MiniMax M3 NVFP4 KV cache on ROCm {reason}")

    def forward(
        self,
        layer: AttentionLayer,
        query: torch.Tensor,
        kv_cache: torch.Tensor,
        output: torch.Tensor,
    ) -> torch.Tensor:
        from vllm.models.minimax_m3.amd.ops.nvfp4_prefill.host import (
            minimax_m3_nvfp4_sparse_prefill,
        )
        from vllm.models.minimax_m3.amd.ops.nvfp4_sparse_decode.host import (
            minimax_m3_nvfp4_sparse_decode_fly,
        )

        attn_metadata = get_forward_context().attn_metadata
        if not isinstance(attn_metadata, dict):
            return output  # profiling run; caches unbound
        md = attn_metadata[layer.layer_name]  # type: ignore[attr-defined]
        assert isinstance(md, MiniMaxM3SparseMetadata)

        nd = md.num_decode_tokens
        num_tokens = md.num_actual_tokens
        topk = layer.topk_indices_buffer  # type: ignore[attr-defined]
        assert topk is not None
        q = query[:num_tokens].view(-1, self.num_heads, self.head_size)
        out = output[:num_tokens].view(-1, self.num_heads, self.head_size)
        k_scale = layer._k_scale  # type: ignore[attr-defined]
        v_scale = layer._v_scale  # type: ignore[attr-defined]

        if md.num_decodes > 0:
            d = md.decode
            assert d is not None
            minimax_m3_nvfp4_sparse_decode_fly(
                q[:nd].contiguous(),
                kv_cache,
                topk[:, :nd, :],
                d.block_table,
                d.seq_lens,
                self.scale,
                out[:nd],
                k_scale=k_scale,
                v_scale=v_scale,
                decode_query_len=d.decode_query_len,
            )
        if md.num_prefills > 0:
            p = md.prefill
            assert p is not None
            assert p.query_req_id is not None and p.query_abs_pos is not None
            minimax_m3_nvfp4_sparse_prefill(
                q[nd:],
                kv_cache,
                topk[:, nd:num_tokens, :],
                p.block_table,
                p.query_req_id,
                p.query_abs_pos,
                self.num_kv_heads,
                self.scale,
                out[nd:],
                k_scale=k_scale,
                v_scale=v_scale,
            )
        return output

MiniMaxM3SparseRocmNvfp4MetadataBuilder

Bases: MiniMaxM3SparseMetadataBuilder

Adds each prefill token's request and absolute position.

Source code in vllm/models/minimax_m3/amd/sparse_attention_nvfp4.py 
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class MiniMaxM3SparseRocmNvfp4MetadataBuilder(MiniMaxM3SparseMetadataBuilder):
    """Adds each prefill token's request and absolute position."""

    def build(
        self,
        common_prefix_len: int,
        common_attn_metadata: CommonAttentionMetadata,
        fast_build: bool = False,
    ) -> MiniMaxM3SparseMetadata:
        metadata = super().build(common_prefix_len, common_attn_metadata, fast_build)
        p = metadata.prefill
        if p is not None and p.query_req_id is None:
            p.query_req_id, p.query_abs_pos = minimax_m3_query_token_positions(
                p.cu_seqlens_q, p.context_lens, metadata.num_prefill_tokens
            )
        return metadata

rocm_nvfp4_unsupported_reason(num_heads, num_kv_heads, head_dim, topk_blocks, block_size)

Why the ROCm NVFP4 attend cannot serve this layer, None when it can.

Source code in vllm/models/minimax_m3/amd/sparse_attention_nvfp4.py 
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def rocm_nvfp4_unsupported_reason(
    num_heads: int, num_kv_heads: int, head_dim: int, topk_blocks: int, block_size: int
) -> str | None:
    """Why the ROCm NVFP4 attend cannot serve this layer, None when it can."""
    from vllm.models.minimax_m3.amd.ops.nvfp4_prefill.host import (
        supports_nvfp4_sparse_prefill,
    )

    if not supports_nvfp4_sparse_prefill(
        num_heads, num_kv_heads, head_dim, topk_blocks, block_size
    ):
        return (
            "needs gfx950, head_dim 128, 16 query heads per KV head and 16 "
            f"selected 128-token blocks (got num_heads={num_heads}, "
            f"num_kv_heads={num_kv_heads}, head_dim={head_dim}, "
            f"topk_blocks={topk_blocks}, block_size={block_size})"
        )
    return None