dcu_mla_backend.py

from __future__ import annotations

from dataclasses import dataclass
from typing import TYPE_CHECKING, Callable, Optional, Tuple, Union

import torch
import triton

from sglang.srt.layers.attention.base_attn_backend import AttentionBackend
from sglang.srt.layers.attention.utils import create_flashmla_kv_indices_triton
from sglang.srt.layers.dp_attention import get_attention_tp_size
from sglang.srt.model_executor.forward_batch_info import ForwardBatch, ForwardMode

try:
    from flash_mla import (
        flash_mla_with_kvcache,
        flash_mla_with_kvcache_quantization,
        get_mla_metadata
    )
    _has_flash_mla = True
except Exception:
    try:
        from vllm.attention.ops.flashmla import (
            flash_mla_with_kvcache,
            get_mla_metadata
        )
        _has_flash_mla = False
    except Exception:
        raise ImportError(
            "Can not import FlashMLA。Please perform the following operations to use flashmla:\n"
            "  pip install flash-mla\n"
            "  or\n"
            "  pip install vllm"
        )

PAGE_SIZE = 64 # 强制64

if TYPE_CHECKING:
    from sglang.srt.layers.radix_attention import RadixAttention
    from sglang.srt.model_executor.model_runner import ModelRunner
    from sglang.srt.speculative.spec_info import SpecInput

@dataclass
class VllmMLADecodeMetadata:
    flashmla_metadata: Optional[Tuple[torch.Tensor, torch.Tensor]] = None
    num_splits: Optional[torch.Tensor] = None
    block_kv_indices: Optional[torch.Tensor] = None

    def __init__(
        self,
        flashmla_metadata: Optional[Tuple[torch.Tensor, torch.Tensor]] = None,
        num_splits: Optional[torch.Tensor] = None,
        block_kv_indices: Optional[torch.Tensor] = None,
    ):
        self.flashmla_metadata = flashmla_metadata
        self.num_splits = num_splits
        self.block_kv_indices = block_kv_indices

class DCUMLABackend(AttentionBackend):

    def __init__(
        self,
        model_runner: "ModelRunner",
        skip_prefill: bool = False,
        kv_indptr_buf: Optional[torch.Tensor] = None,
        kv_last_page_len_buf: Optional[torch.Tensor] = None,
    ):
        super().__init__()
        
        if model_runner.server_args.page_size != PAGE_SIZE:
            raise ValueError(
                f"dcu_mla backend requires page_size={PAGE_SIZE}, "
                f"but got the {model_runner.server_args.page_size}"
            )

        self.num_q_heads = (
            model_runner.model_config.num_attention_heads // get_attention_tp_size()
        )
        self.req_to_token = model_runner.req_to_token_pool.req_to_token
        
        self.kv_lora_rank = model_runner.model_config.kv_lora_rank
        self.qk_nope_head_dim = model_runner.model_config.qk_nope_head_dim
        self.qk_rope_head_dim = model_runner.model_config.qk_rope_head_dim
        self.v_head_dim = model_runner.model_config.v_head_dim
        self.kv_cache_dim = self.kv_lora_rank + self.qk_rope_head_dim
        
        self.data_type = model_runner.kv_cache_dtype
        self.q_data_type = model_runner.dtype
        
        self.device = model_runner.device
        self.k_scale = torch.tensor([1.0], dtype=torch.float32, device=self.device)
        self.max_context_len = model_runner.model_config.context_len
        self.num_draft_tokens = model_runner.server_args.speculative_num_draft_tokens
        
        self.forward_metadata: Union[VllmMLADecodeMetadata] = None
        
        self.skip_prefill = skip_prefill
        if not skip_prefill:
            from sglang.srt.layers.attention.flashattention_backend import FlashAttentionBackend
            self.flashattn_backend = FlashAttentionBackend(
                model_runner,
                skip_prefill=False,
            )

    def _build_decode_metadata(
        self, 
        forward_batch: ForwardBatch,
        seq_lens: torch.Tensor
    ) -> Tuple[Tuple[torch.Tensor, torch.Tensor], torch.Tensor, torch.Tensor]:

        bs = forward_batch.batch_size
        max_seqlen_pad = triton.cdiv(seq_lens.max().item(), PAGE_SIZE)
        
        # 参考vllm官方博客分页
        block_kv_indices = torch.full(
            (bs, max_seqlen_pad), -1, dtype=torch.int32, device=seq_lens.device
        )
        create_flashmla_kv_indices_triton[(bs,)](
            self.req_to_token,
            forward_batch.req_pool_indices,
            seq_lens,
            None,
            block_kv_indices,
            self.req_to_token.stride(0),
            max_seqlen_pad,
        )

        mla_metadata, num_splits = get_mla_metadata(
            seq_lens.to(torch.int32), self.num_q_heads, 1
        )
        return (mla_metadata, num_splits), num_splits, block_kv_indices

    def init_forward_metadata(self, forward_batch: ForwardBatch):

        if forward_batch.forward_mode.is_decode_or_idle():
            # decode用flashmla
            (mla_metadata, num_splits), num_splits_t, block_kv_indices = (
                self._build_decode_metadata(forward_batch, forward_batch.seq_lens)
            )
            self.forward_metadata = VllmMLADecodeMetadata(
                mla_metadata, num_splits_t, block_kv_indices
            )
        elif forward_batch.forward_mode.is_target_verify():
            seq_lens = forward_batch.seq_lens + self.num_draft_tokens
            (mla_metadata, num_splits), num_splits_t, block_kv_indices = (
                self._build_decode_metadata(forward_batch, seq_lens)
            )
            self.forward_metadata = VllmMLADecodeMetadata(
                mla_metadata, num_splits_t, block_kv_indices
            )
        else:
            if not self.skip_prefill:
                self.flashattn_backend.init_forward_metadata(forward_batch)

    def init_cuda_graph_state(
        self,
        max_bs: int,
        max_num_tokens: int,
        block_kv_indices: Optional[torch.Tensor] = None,
    ):
        if block_kv_indices is None:
            cuda_graph_kv_indices = torch.full(
                (max_bs, (self.max_context_len + PAGE_SIZE) // PAGE_SIZE),
                1,
                dtype=torch.int32,
                device="cuda",
            )
        else:
            cuda_graph_kv_indices = block_kv_indices

        if self.num_draft_tokens:
            mla_metadata, num_splits = get_mla_metadata(
                torch.ones(max_bs, dtype=torch.int32, device=cuda_graph_kv_indices.device),
                self.num_draft_tokens * self.num_q_heads,
                1,
            )
        else:
            mla_metadata, num_splits = get_mla_metadata(
                torch.ones(max_bs, dtype=torch.int32, device=cuda_graph_kv_indices.device),
                self.num_q_heads,
                1,
            )

        self.cuda_graph_mla_metadata = mla_metadata
        self.cuda_graph_num_splits = num_splits
        self.cuda_graph_kv_indices = cuda_graph_kv_indices

    def init_forward_metadata_capture_cuda_graph(
        self,
        bs: int,
        num_tokens: int,
        req_pool_indices: torch.Tensor,
        seq_lens: torch.Tensor,
        encoder_lens: Optional[torch.Tensor],
        forward_mode: ForwardMode,
        spec_info: Optional["SpecInput"],
    ):
        if forward_mode.is_decode_or_idle():
            max_seqlen_pad = triton.cdiv(seq_lens.max().item(), PAGE_SIZE)
            create_flashmla_kv_indices_triton[(bs,)](
                self.req_to_token,
                req_pool_indices,
                seq_lens,
                None,
                self.cuda_graph_kv_indices,
                self.req_to_token.stride(0),
                self.cuda_graph_kv_indices.stride(0),
            )
            num_q_heads = self.num_q_heads * (self.num_draft_tokens or 1)
            mla_metadata, num_splits = get_mla_metadata(
                seq_lens.to(torch.int32), num_q_heads, 1
            )
            self.cuda_graph_mla_metadata.copy_(mla_metadata)
            self.cuda_graph_num_splits[: bs + 1].copy_(num_splits)
            self.forward_metadata = VllmMLADecodeMetadata(
                self.cuda_graph_mla_metadata,
                self.cuda_graph_num_splits[: bs + 1],
                self.cuda_graph_kv_indices[:bs, :max_seqlen_pad],
            )
        elif forward_mode.is_target_verify():
            seq_lens = seq_lens + self.num_draft_tokens
            max_seqlen_pad = triton.cdiv(seq_lens.max().item(), PAGE_SIZE)
            create_flashmla_kv_indices_triton[(bs,)](
                self.req_to_token,
                req_pool_indices,
                seq_lens,
                None,
                self.cuda_graph_kv_indices,
                self.req_to_token.stride(0),
                self.cuda_graph_kv_indices.stride(0),
            )
            mla_metadata, num_splits = get_mla_metadata(
                seq_lens.to(torch.int32), self.num_draft_tokens * self.num_q_heads, 1
            )
            self.cuda_graph_mla_metadata.copy_(mla_metadata)
            self.cuda_graph_num_splits[: bs + 1].copy_(num_splits)
            self.forward_metadata = VllmMLADecodeMetadata(
                self.cuda_graph_mla_metadata,
                self.cuda_graph_num_splits[: bs + 1],
                self.cuda_graph_kv_indices[:bs, :max_seqlen_pad],
            )
        else:
            if not self.skip_prefill:
                self.flashattn_backend.init_forward_metadata_capture_cuda_graph(
                    bs,
                    num_tokens,
                    req_pool_indices,
                    seq_lens,
                    encoder_lens,
                    forward_mode,
                    spec_info,
                )

    def init_forward_metadata_replay_cuda_graph(
        self,
        bs: int,
        req_pool_indices: torch.Tensor,
        seq_lens: torch.Tensor,
        seq_lens_sum: int,
        encoder_lens: Optional[torch.Tensor],
        forward_mode: ForwardMode,
        spec_info: Optional["SpecInput"],
        seq_lens_cpu: Optional[torch.Tensor],
    ):
        if forward_mode.is_decode_or_idle():
            assert seq_lens_cpu is not None
            seq_lens = seq_lens[:bs]
            seq_lens_cpu = seq_lens_cpu[:bs]
            max_seqlen_pad = triton.cdiv(seq_lens_cpu.max().item(), PAGE_SIZE)
            create_flashmla_kv_indices_triton[(bs,)](
                self.req_to_token,
                req_pool_indices[:bs],
                seq_lens,
                None,
                self.cuda_graph_kv_indices,
                self.req_to_token.stride(0),
                self.cuda_graph_kv_indices.stride(0),
            )
            num_q_heads = self.num_q_heads * (self.num_draft_tokens or 1)
            mla_metadata, num_splits = get_mla_metadata(
                seq_lens.to(torch.int32), num_q_heads, 1
            )
            self.cuda_graph_mla_metadata.copy_(mla_metadata)
            self.cuda_graph_num_splits[: bs + 1].copy_(num_splits)
            self.forward_metadata.flashmla_metadata = self.cuda_graph_mla_metadata
            self.forward_metadata.num_splits = self.cuda_graph_num_splits[: bs + 1]
            self.forward_metadata.block_kv_indices = self.cuda_graph_kv_indices[
                :bs, :max_seqlen_pad
            ]
        elif forward_mode.is_target_verify():
            seq_lens = seq_lens[:bs] + self.num_draft_tokens
            seq_lens_cpu = seq_lens_cpu[:bs] + self.num_draft_tokens
            max_seqlen_pad = triton.cdiv(seq_lens_cpu.max().item(), PAGE_SIZE)
            create_flashmla_kv_indices_triton[(bs,)](
                self.req_to_token,
                req_pool_indices[:bs],
                seq_lens,
                None,
                self.cuda_graph_kv_indices,
                self.req_to_token.stride(0),
                self.cuda_graph_kv_indices.stride(0),
            )
            mla_metadata, num_splits = get_mla_metadata(
                seq_lens.to(torch.int32), self.num_draft_tokens * self.num_q_heads, 1
            )
            self.cuda_graph_mla_metadata.copy_(mla_metadata)
            self.cuda_graph_num_splits[: bs + 1].copy_(num_splits)
            self.forward_metadata.flashmla_metadata = self.cuda_graph_mla_metadata
            self.forward_metadata.num_splits = self.cuda_graph_num_splits[: bs + 1]
            self.forward_metadata.block_kv_indices = self.cuda_graph_kv_indices[
                :bs, :max_seqlen_pad
            ]
        else:
            if not self.skip_prefill:
                self.flashattn_backend.init_forward_metadata_replay_cuda_graph(
                    bs,
                    req_pool_indices,
                    seq_lens,
                    seq_lens_sum,
                    encoder_lens,
                    forward_mode,
                    spec_info,
                    seq_lens_cpu,
                )

    def get_cuda_graph_seq_len_fill_value(self):
        return 1

    def _call_decode(self, reshape_q: torch.Tensor, k_cache_reshaped: torch.Tensor,
                          block_table: torch.Tensor, cache_seqlens: torch.Tensor,
                          scaling: float):
        o, _ = flash_mla_with_kvcache(
            q=reshape_q,
            k_cache=k_cache_reshaped,
            block_table=block_table,
            cache_seqlens=cache_seqlens,
            head_dim_v=self.kv_lora_rank,
            tile_scheduler_metadata=self.forward_metadata.flashmla_metadata,
            num_splits=self.forward_metadata.num_splits,
            softmax_scale=scaling,
            causal=True,
        )
        return o

    def _call_fp8_decode(self, reshape_q: torch.Tensor, k_cache_reshaped: torch.Tensor,
                            block_table: torch.Tensor, cache_seqlens: torch.Tensor,
                            scaling: float, k_scale=None, kv_cache_dtype=None):
        assert _has_flash_mla, "FP8 KV cache 需要flash_mla包"
        o, _ = flash_mla_with_kvcache_quantization(
            q=reshape_q,
            k_cache=k_cache_reshaped,
            block_table=block_table,
            cache_seqlens=cache_seqlens,
            head_dim_v=self.kv_lora_rank,
            tile_scheduler_metadata=self.forward_metadata.flashmla_metadata,
            num_splits=self.forward_metadata.num_splits,
            softmax_scale=scaling,
            causal=True,
            k_scale=k_scale,
            kv_cache_dtype=kv_cache_dtype,
        )
        return o

    @torch._dynamo.disable()
    def forward_decode(
        self,
        q: torch.Tensor,
        k: torch.Tensor,
        v: torch.Tensor,
        layer: "RadixAttention",
        forward_batch: ForwardBatch,
        save_kv_cache: bool = True,
    ):
        cache_loc = forward_batch.out_cache_loc

        if k is not None:
            assert v is not None
            if save_kv_cache:
                forward_batch.token_to_kv_pool.set_kv_buffer(
                    layer,
                    cache_loc,
                    k,
                    v,
                )

        bs = forward_batch.batch_size
        k_cache = forward_batch.token_to_kv_pool.get_key_buffer(layer.layer_id)

        reshape_q = q.view(bs, -1, layer.tp_q_head_num, layer.head_dim)
        k_cache_reshaped = k_cache.view(-1, PAGE_SIZE, 1, self.kv_cache_dim)

        if self.data_type in (torch.float8_e4m3fn, torch.float8_e4m3fnuz, 
                              torch.float8_e5m2, torch.float8_e5m2fnuz):
            if self.data_type in (torch.float8_e4m3fnuz, torch.float8_e4m3fn):
                kv_cache_dtype="fp8_e4m3"
            else:
                kv_cache_dtype="fp8_e5m2"
            k_scale = layer.k_scale if layer.k_scale is not None else self.k_scale
            o = self._call_fp8_decode(
                reshape_q, 
                k_cache_reshaped, 
                self.forward_metadata.block_kv_indices[:bs],
                forward_batch.seq_lens.to(torch.int32), 
                layer.scaling, 
                k_scale, 
                kv_cache_dtype=kv_cache_dtype,
            )
        else:
            o = self._call_decode(
                reshape_q, 
                k_cache_reshaped, 
                self.forward_metadata.block_kv_indices[:bs],
                forward_batch.seq_lens.to(torch.int32), 
                layer.scaling,
            )

        return o.view(-1, layer.tp_q_head_num * layer.v_head_dim)

    @torch._dynamo.disable()  # NOTE: untested
    def forward_extend(
        self,
        q: torch.Tensor,
        k: torch.Tensor,
        v: torch.Tensor,
        layer: "RadixAttention",
        forward_batch: ForwardBatch,
        save_kv_cache: bool = True,
        # For multi-head latent attention
        q_rope: Optional[torch.Tensor] = None,
        k_rope: Optional[torch.Tensor] = None,
        sinks=None,
    ):
        if save_kv_cache:
            return self.forward_decode(q,k,v,layer,forward_batch, save_kv_cache)
    
        if ((
            forward_batch.forward_mode == ForwardMode.EXTEND
            or forward_batch.forward_mode == ForwardMode.DRAFT_EXTEND)
        ):
            if not self.skip_prefill:
                return self.flashattn_backend.forward_extend(
                            q, k, v, layer, forward_batch, save_kv_cache, q_rope, k_rope, sinks
                        )
            else:
                raise RuntimeError("skip prefill but use forward_extend")

        cache_loc = forward_batch.out_cache_loc
        if k is not None:
            assert v is not None
            if save_kv_cache:
                forward_batch.token_to_kv_pool.set_kv_buffer(layer, cache_loc, k, v)

        bs = forward_batch.batch_size
        k_cache = forward_batch.token_to_kv_pool.get_key_buffer(layer.layer_id)

        reshape_q = q.view(bs, -1, layer.tp_q_head_num, layer.head_dim)
        k_cache_reshaped = k_cache.view(-1, PAGE_SIZE, 1, self.kv_cache_dim)

        if self.data_type in (torch.float8_e4m3fn, torch.float8_e4m3fnuz, 
                              torch.float8_e5m2, torch.float8_e5m2fnuz):
            if self.data_type in (torch.float8_e4m3fnuz, torch.float8_e4m3fn):
                kv_cache_dtype="fp8_e4m3"
            else:
                kv_cache_dtype="fp8_e5m2"
            k_scale = layer.k_scale if layer.k_scale is not None else self.k_scale
            o = self._call_fp8_decode(
                reshape_q, 
                k_cache_reshaped, 
                self.forward_metadata.block_kv_indices[:bs],
                (forward_batch.seq_lens + self.num_draft_tokens).to(torch.int32),
                layer.scaling,
                k_scale,
                kv_cache_dtype=kv_cache_dtype,
            )
        else:
            o = self._call_decode(
                reshape_q, 
                k_cache_reshaped, 
                self.forward_metadata.block_kv_indices[:bs],
                (forward_batch.seq_lens + self.num_draft_tokens).to(torch.int32),
                layer.scaling,
            )

        return o.view(-1, layer.tp_q_head_num * layer.v_head_dim)


class DCUMLAMultiStepDraftBackend:
    """
    Wrap multiple flashmla attention backends as one for multiple consecutive
    draft decoding steps.
    """

    def __init__(
        self,
        model_runner: ModelRunner,
        topk: int,
        speculative_num_steps: int,
    ):
        if topk > 1:
            raise ValueError(
                "Currently FlashMLA only supports topk=1 for speculative decoding"
            )
        self.topk = topk
        self.speculative_num_steps = speculative_num_steps
        max_bs = model_runner.req_to_token_pool.size * self.topk
        self.kv_indptr = torch.zeros(
            (
                self.speculative_num_steps,
                max_bs + 1,
            ),
            dtype=torch.int32,
            device=model_runner.device,
        )

        self.attn_backends = []
        for i in range(self.speculative_num_steps - 1):
            self.attn_backends.append(
                DCUMLABackend(
                    model_runner,
                    skip_prefill=True,
                    kv_indptr_buf=self.kv_indptr[i],
                    kv_last_page_len_buf=None,
                )
            )

    def common_template(
        self,
        forward_batch: ForwardBatch,
        call_fn: Callable,
    ):
        assert forward_batch.spec_info is not None

        for i in range(self.speculative_num_steps - 1):
            call_fn(i, forward_batch)

    def init_forward_metadata(self, forward_batch: ForwardBatch):
        def call_fn(i, forward_batch):
            assert forward_batch.spec_info is not None
            self.attn_backends[i].init_forward_metadata(forward_batch)

        self.common_template(forward_batch, call_fn)

    def init_cuda_graph_state(self, max_bs: int, max_num_tokens: int):
        for i in range(self.speculative_num_steps - 1):
            self.attn_backends[i].init_cuda_graph_state(
                max_bs, max_num_tokens, block_kv_indices=None
            )

    def init_forward_metadata_capture_cuda_graph(self, forward_batch: ForwardBatch):
        def call_fn(i, forward_batch):
            self.attn_backends[i].init_forward_metadata_capture_cuda_graph(
                forward_batch.batch_size,
                forward_batch.batch_size * self.topk,
                forward_batch.req_pool_indices,
                forward_batch.seq_lens,
                encoder_lens=None,
                forward_mode=ForwardMode.DECODE,
                spec_info=forward_batch.spec_info,
            )

        self.common_template(forward_batch, call_fn)

    def init_forward_metadata_replay_cuda_graph(
        self, forward_batch: ForwardBatch, bs: int
    ):
        def call_fn(i, forward_batch):
            self.attn_backends[i].init_forward_metadata_replay_cuda_graph(
                bs,
                forward_batch.req_pool_indices,
                forward_batch.seq_lens,
                seq_lens_sum=-1,
                encoder_lens=None,
                forward_mode=ForwardMode.DECODE,
                spec_info=forward_batch.spec_info,
                seq_lens_cpu=forward_batch.seq_lens_cpu,
            )

        self.common_template(forward_batch, call_fn)