cudagraph_utils.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
from collections.abc import Callable
from typing import Any

import torch
import torch.nn as nn
from tqdm import tqdm

from vllm.config import VllmConfig
from vllm.config.compilation import CUDAGraphMode
from vllm.distributed.parallel_state import graph_capture, is_global_first_rank
from vllm.forward_context import BatchDescriptor, set_forward_context
from vllm.model_executor.offloader.base import get_offloader
from vllm.utils.math_utils import cdiv
from vllm.v1.kv_cache_interface import KVCacheConfig
from vllm.v1.worker.gpu.attn_utils import build_slot_mappings_by_layer
from vllm.v1.worker.gpu.block_table import BlockTables
from vllm.v1.worker.gpu.cp_utils import prepare_dcp_local_seq_lens
from vllm.v1.worker.gpu.dp_utils import make_num_tokens_across_dp
from vllm.v1.worker.gpu.input_batch import InputBatch, InputBuffers
from vllm.v1.worker.gpu.model_states.interface import ModelState
from vllm.v1.worker.utils import AttentionGroup


class CudaGraphManager:
    def __init__(
        self,
        vllm_config: VllmConfig,
        use_aux_hidden_state_outputs: bool,
        device: torch.device,
    ):
        self.vllm_config = vllm_config
        self.scheduler_config = vllm_config.scheduler_config
        self.use_aux_hidden_state_outputs = use_aux_hidden_state_outputs
        self.device = device

        self.max_model_len = vllm_config.model_config.max_model_len
        self.max_num_reqs = self.scheduler_config.max_num_seqs
        self.max_num_tokens = self.scheduler_config.max_num_batched_tokens
        self.dp_size = vllm_config.parallel_config.data_parallel_size

        self.uniform_decode_query_len = 1
        spec_config = vllm_config.speculative_config
        if spec_config is not None:
            self.uniform_decode_query_len += spec_config.num_speculative_tokens

        self.compilation_config = vllm_config.compilation_config
        assert self.compilation_config is not None
        self.cudagraph_mode = self.compilation_config.cudagraph_mode

        use_uniform_decode_cudagraph = (
            self.cudagraph_mode.decode_mode() == CUDAGraphMode.FULL
            and self.cudagraph_mode.separate_routine()
        )
        self.cudagraph_sizes, self.uniform_decode_cudagraph_sizes = get_cudagraph_sizes(
            self.compilation_config.cudagraph_capture_sizes,
            self.max_num_reqs,
            self.max_num_tokens,
            self.cudagraph_mode,
            self.uniform_decode_query_len,
            use_uniform_decode_cudagraph,
        )

        self.graphs: dict[int, torch.cuda.CUDAGraph] = {}
        self.pool = None
        if self.cudagraph_mode != CUDAGraphMode.NONE:
            self.pool = torch.cuda.graph_pool_handle()
        self.hidden_states: torch.Tensor | None = None
        self.aux_hidden_states: list[torch.Tensor] = []

    def needs_capture(self) -> bool:
        return len(self.cudagraph_sizes) > 0

    def get_cudagraph_size(
        self, num_tokens: int, uniform_decode: bool = False
    ) -> int | None:
        if uniform_decode and self.uniform_decode_cudagraph_sizes:
            return self.uniform_decode_cudagraph_sizes.get(num_tokens)
        return self.cudagraph_sizes.get(num_tokens)

    def capture_graph(
        self,
        num_tokens: int,
        capture_cg_mode: CUDAGraphMode,
        model: nn.Module,
        model_state: ModelState,
        input_buffers: InputBuffers,
        block_tables: BlockTables,
        attn_groups: list[list[AttentionGroup]],
        kv_cache_config: KVCacheConfig,
        has_lora: bool = False,
        uniform_decode: bool = False,
    ) -> None:
        # select and check capture function
        assert capture_cg_mode in [CUDAGraphMode.PIECEWISE, CUDAGraphMode.FULL], (
            f"Invalid capture_cudagraph_mode for capture: {capture_cg_mode}"
        )
        if capture_cg_mode == CUDAGraphMode.PIECEWISE:
            capture_fn = self._capture_piecewise_graph
        else:
            capture_fn = self._capture_full_graph
        # prepare inputs
        if uniform_decode:
            num_reqs = min(
                cdiv(num_tokens, self.uniform_decode_query_len),
                self.max_num_reqs,
            )
        else:
            num_reqs = min(num_tokens, self.max_num_reqs)

        model_inputs = {
            "input_ids": input_buffers.input_ids[:num_tokens],
            "positions": input_buffers.positions[:num_tokens],
            # NOTE: Values returned by `prepare_dummy_inputs` will override the
            # default values above.
            **model_state.prepare_dummy_inputs(num_reqs, num_tokens),
        }

        attn_metadata, slot_mappings = prepare_inputs_to_capture(
            num_reqs,
            num_tokens,
            model_state,
            input_buffers,
            block_tables,
            attn_groups,
            kv_cache_config,
        )
        num_tokens_across_dp = make_num_tokens_across_dp(self.dp_size, num_tokens)

        # Warm up.
        with set_forward_context(
            attn_metadata,
            self.vllm_config,
            num_tokens=num_tokens,
            cudagraph_runtime_mode=CUDAGraphMode.NONE,
            num_tokens_across_dp=num_tokens_across_dp,
            slot_mapping=slot_mappings,
        ):
            model_output = model(**model_inputs)
            if self.use_aux_hidden_state_outputs:
                hidden_states, aux_hidden_states = model_output
            else:
                hidden_states = model_output
                aux_hidden_states = None

        # Allocate output buffers if not already done.
        if self.hidden_states is None:
            self.hidden_states = torch.empty_like(hidden_states)
        if self.use_aux_hidden_state_outputs and not self.aux_hidden_states:
            self.aux_hidden_states = [torch.empty_like(x) for x in aux_hidden_states]

        capture_fn(
            num_tokens=num_tokens,
            num_reqs=num_reqs,
            model=model,
            model_inputs=model_inputs,
            num_tokens_across_dp=num_tokens_across_dp,
            attn_metadata=attn_metadata,
            slot_mappings=slot_mappings,
            has_lora=has_lora,
        )

    def _capture_full_graph(
        self,
        num_tokens: int,
        num_reqs: int,
        model: nn.Module,
        model_inputs: dict[str, torch.Tensor | None],
        num_tokens_across_dp: torch.Tensor,
        attn_metadata: dict[str, Any] | None,
        slot_mappings: dict[str, torch.Tensor] | None,
        has_lora: bool = False,
    ) -> None:
        assert attn_metadata is not None
        # Capture the graph.
        assert num_tokens not in self.graphs
        graph = torch.cuda.CUDAGraph()

        # Sync offloader's copy stream before capture.
        # Ensure any pre-capture prefetches from offloader are complete.
        get_offloader().sync_prev_onload()

        with (
            set_forward_context(
                attn_metadata=attn_metadata,
                vllm_config=self.vllm_config,
                num_tokens=num_tokens,
                cudagraph_runtime_mode=CUDAGraphMode.NONE,
                num_tokens_across_dp=num_tokens_across_dp,
                slot_mapping=slot_mappings,
            ),
            torch.cuda.graph(graph, self.pool),
        ):
            model_output = model(**model_inputs)

            # Join offloader's copy stream after forward to avoid unjoined
            # stream error. The last layer's start_prefetch forks copy_stream,
            # but wait_prefetch only happens in the next forward pass.
            get_offloader().join_after_forward()

            if self.use_aux_hidden_state_outputs:
                hidden_states, aux_hidden_states = model_output
            else:
                hidden_states = model_output
                aux_hidden_states = None

            # Copy outputs to the output buffers.
            assert self.hidden_states is not None
            self.hidden_states[:num_tokens] = hidden_states
            if self.use_aux_hidden_state_outputs:
                for i, aux_hidden in enumerate(aux_hidden_states):
                    self.aux_hidden_states[i][:num_tokens] = aux_hidden
        self.graphs[num_tokens] = graph

    def _capture_piecewise_graph(
        self,
        num_tokens: int,
        num_reqs: int,
        model: nn.Module,
        model_inputs: dict[str, torch.Tensor | None],
        num_tokens_across_dp: torch.Tensor,
        attn_metadata: dict[str, Any] | None,
        slot_mappings: dict[str, torch.Tensor] | None,
        has_lora: bool = False,
    ) -> None:
        # create batch descriptor for piecewise cudagraph dispatch key
        batch_descriptor = BatchDescriptor(num_tokens=num_tokens, has_lora=has_lora)

        # Capture run - CUDAGraphWrapper inside torch.compile will auto capture.
        with set_forward_context(
            attn_metadata=None,  # piecewise no need attn_metadata
            vllm_config=self.vllm_config,
            num_tokens=num_tokens,
            cudagraph_runtime_mode=CUDAGraphMode.PIECEWISE,
            num_tokens_across_dp=num_tokens_across_dp,
            batch_descriptor=batch_descriptor,
            slot_mapping=slot_mappings,
        ):
            model(**model_inputs)

    @torch.inference_mode()
    def capture(
        self,
        model: nn.Module,
        model_state: ModelState,
        input_buffers: InputBuffers,
        block_tables: BlockTables,
        attn_groups: list[list[AttentionGroup]],
        kv_cache_config: KVCacheConfig,
        has_lora: bool = False,
    ) -> None:
        common_kwargs = dict(
            device=self.device,
            capture_fn=self.capture_graph,
            model=model,
            model_state=model_state,
            input_buffers=input_buffers,
            block_tables=block_tables,
            attn_groups=attn_groups,
            kv_cache_config=kv_cache_config,
            has_lora=has_lora,
        )

        # Phase 1: Capture for mixed prefill-decode batches if needed.
        mixed_mode = self.cudagraph_mode.mixed_mode()
        if mixed_mode != CUDAGraphMode.NONE:
            capture_graphs(
                cudagraph_sizes=self.cudagraph_sizes,
                capture_cudagraph_mode=mixed_mode,
                desc=f"Capturing CUDA graphs (mixed, {mixed_mode.name})",
                uniform_decode=False,
                **common_kwargs,
            )

        # Phase 2: Capture FULL graphs for uniform decode batches if needed.
        # This is only needed if we use a separate routine for decode batches
        # and the decode_mode is FULL.
        if self.uniform_decode_cudagraph_sizes:
            capture_graphs(
                cudagraph_sizes=self.uniform_decode_cudagraph_sizes,
                capture_cudagraph_mode=CUDAGraphMode.FULL,
                desc="Capturing CUDA graphs (decode, FULL)",
                uniform_decode=True,
                **common_kwargs,
            )

    def get_cudagraph_runtime_mode(
        self, num_reqs: int, num_tokens: int, max_query_len: int
    ) -> tuple[CUDAGraphMode, int | None]:
        is_uniform_decode = (max_query_len == self.uniform_decode_query_len) and (
            num_tokens == max_query_len * num_reqs
        )

        cudagraph_size = self.get_cudagraph_size(num_tokens, is_uniform_decode)
        if cudagraph_size is None:
            cudagraph_mode = CUDAGraphMode.NONE
        elif is_uniform_decode:
            cudagraph_mode = self.cudagraph_mode.decode_mode()
        else:
            cudagraph_mode = self.cudagraph_mode.mixed_mode()

        if (
            cudagraph_mode == CUDAGraphMode.FULL
            and cudagraph_size is not None
            and cudagraph_size not in self.graphs
        ):
            # If graph wasn't captured yet, fall back to eager.
            # This might happen when the dummy run is called before capture.
            cudagraph_mode = CUDAGraphMode.NONE
            cudagraph_size = None
        return cudagraph_mode, cudagraph_size

    def run_fullgraph(
        self, num_tokens: int
    ) -> torch.Tensor | tuple[torch.Tensor, list[torch.Tensor]]:
        assert num_tokens in self.graphs, f"No cudagraph for {num_tokens} tokens"
        # Sync offloader before replay - needed when transitioning from
        # eager/piecewise to full cudagraph (e.g., prefill → decode).
        # The previous eager iteration's start_prefetch may have queued
        # H2D copies on copy_stream that the graph's captured events
        # cannot see. Without this, replay could overwrite static buffers
        # while those copies are still in flight.
        get_offloader().sync_prev_onload()
        self.graphs[num_tokens].replay()
        assert self.hidden_states is not None
        hidden_states = self.hidden_states[:num_tokens]
        if not self.use_aux_hidden_state_outputs:
            return hidden_states
        return hidden_states, [x[:num_tokens] for x in self.aux_hidden_states]


def get_cudagraph_sizes(
    capture_sizes: list[int] | None,
    max_num_reqs: int,
    max_num_tokens: int,
    cudagraph_mode: CUDAGraphMode,
    uniform_decode_query_len: int = 1,
    uniform_decode_cudagraph: bool = False,
) -> tuple[dict[int, int], dict[int, int]]:
    # Support both FULL and PIECEWISE cudagraph modes
    if cudagraph_mode == CUDAGraphMode.NONE:
        return {}, {}
    if not capture_sizes:
        return {}, {}

    capture_sizes = sorted(capture_sizes)
    if not capture_sizes:
        return {}, {}

    cudagraph_sizes: dict[int, int] = {}
    for i in range(1, capture_sizes[-1] + 1):
        for x in capture_sizes:
            if i <= x:
                cudagraph_sizes[i] = x
                break

    uniform_decode_cudagraph_sizes: dict[int, int] = {}
    if uniform_decode_cudagraph:
        max_num_tokens = max_num_reqs * uniform_decode_query_len
        uniform_decode_cudagraph_sizes = {
            k: v
            for k, v in cudagraph_sizes.items()
            if v <= max_num_tokens and v >= uniform_decode_query_len
        }
    return cudagraph_sizes, uniform_decode_cudagraph_sizes


def capture_graphs(
    cudagraph_sizes: dict[int, int],
    device: torch.device,
    capture_fn: Callable,
    capture_cudagraph_mode: CUDAGraphMode,
    desc: str = "Capturing CUDA graphs",
    **capture_kwargs,
) -> None:
    # Capture larger graphs first.
    sizes_to_capture = sorted(set(cudagraph_sizes.values()), reverse=True)
    if is_global_first_rank():
        sizes_to_capture = tqdm(sizes_to_capture, desc=desc)

    with graph_capture(device=device):
        for size in sizes_to_capture:
            capture_fn(size, capture_cudagraph_mode, **capture_kwargs)


def prepare_inputs_to_capture(
    num_reqs: int,
    num_tokens: int,
    model_state: ModelState,
    input_buffers: InputBuffers,
    block_tables: BlockTables,
    attn_groups: list[list[AttentionGroup]],
    kv_cache_config: KVCacheConfig,
) -> tuple[dict[str, Any], dict[str, torch.Tensor]]:
    input_batch = InputBatch.make_dummy(num_reqs, num_tokens, input_buffers)
    input_block_tables = block_tables.get_dummy_block_tables(num_reqs)
    slot_mappings = block_tables.get_dummy_slot_mappings(num_tokens)
    slot_mappings_by_layer = build_slot_mappings_by_layer(
        slot_mappings, kv_cache_config
    )

    # HACK(woosuk): Special handling for DCP.
    if block_tables.cp_size > 1:
        prepare_dcp_local_seq_lens(
            input_buffers.dcp_local_seq_lens,
            input_batch.seq_lens,
            num_reqs,
            block_tables.cp_size,
            block_tables.cp_rank,
            block_tables.cp_interleave,
        )
        input_batch.dcp_local_seq_lens = input_buffers.dcp_local_seq_lens[:num_reqs]

    attn_metadata = model_state.prepare_attn(
        input_batch,
        input_block_tables,
        slot_mappings,
        attn_groups,
        kv_cache_config,
    )
    return attn_metadata, slot_mappings_by_layer