llm_engine.py

import time
from functools import partial
from typing import Any, List, Optional, TYPE_CHECKING

from vllm.config import (CacheConfig, ModelConfig, ParallelConfig,
                         SchedulerConfig)
from vllm.core.scheduler import Scheduler
from vllm.engine.arg_utils import EngineArgs
from vllm.engine.ray_utils import initialize_cluster, ray, RayWorker
from vllm.logger import init_logger
from vllm.outputs import RequestOutput
from vllm.sampling_params import SamplingParams
from vllm.sequence import Sequence, SequenceGroup, SequenceStatus
from vllm.transformers_utils.tokenizer import (detokenize_incrementally,
                                               get_tokenizer)
from vllm.utils import Counter

if ray:
    from ray.air.util.torch_dist import init_torch_dist_process_group
    from ray.util.scheduling_strategies import PlacementGroupSchedulingStrategy

if TYPE_CHECKING:
    from ray.util.placement_group import PlacementGroup

logger = init_logger(__name__)


class LLMEngine:
    """An LLM engine that receives requests and generates texts.

    This is the main class for the vLLM engine. It receives requests
    from clients and generates texts from the LLM. It includes a tokenizer, a
    language model (possibly distributed across multiple GPUs), and GPU memory
    space allocated for intermediate states (aka KV cache). This class utilizes
    iteration-level scheduling and efficient memory management to maximize the
    serving throughput.

    The `LLM` class wraps this class for offline batched inference and the
    `AsyncLLMEngine` class wraps this class for online serving.

    NOTE: The config arguments are derived from the `EngineArgs` class. For the
    comprehensive list of arguments, see `EngineArgs`.

    Args:
        model_config: The configuration related to the LLM model.
        cache_config: The configuration related to the KV cache memory
            management.
        parallel_config: The configuration related to distributed execution.
        scheduler_config: The configuration related to the request scheduler.
        distributed_init_method: The initialization method for distributed
            execution. See `torch.distributed.init_process_group` for details.
        stage_devices: The list of devices for each stage. Each stage is a list
            of (rank, node_resource, device) tuples.
        log_stats: Whether to log statistics.
    """

    def __init__(
        self,
        model_config: ModelConfig,
        cache_config: CacheConfig,
        parallel_config: ParallelConfig,
        scheduler_config: SchedulerConfig,
        distributed_init_method: str,
        placement_group: Optional["PlacementGroup"],
        log_stats: bool,
    ) -> None:
        logger.info(
            "Initializing an LLM engine with config: "
            f"model={model_config.model!r}, "
            f"tokenizer={model_config.tokenizer!r}, "
            f"tokenizer_mode={model_config.tokenizer_mode}, "
            f"trust_remote_code={model_config.trust_remote_code}, "
            f"dtype={model_config.dtype}, "
            f"use_dummy_weights={model_config.use_dummy_weights}, "
            f"download_dir={model_config.download_dir!r}, "
            f"use_np_weights={model_config.use_np_weights}, "
            f"tensor_parallel_size={parallel_config.tensor_parallel_size}, "
            f"seed={model_config.seed})")
        # TODO(woosuk): Print more configs in debug mode.

        self.model_config = model_config
        self.cache_config = cache_config
        self.parallel_config = parallel_config
        self.scheduler_config = scheduler_config
        self.log_stats = log_stats
        self._verify_args()

        self.tokenizer = get_tokenizer(
            model_config.tokenizer,
            tokenizer_mode=model_config.tokenizer_mode,
            trust_remote_code=model_config.trust_remote_code)
        self.seq_counter = Counter()

        # Create the parallel GPU workers.
        if self.parallel_config.worker_use_ray:
            self._init_workers_ray(placement_group)
        else:
            self._init_workers(distributed_init_method)

        # Profile the memory usage and initialize the cache.
        self._init_cache()

        # Create the scheduler.
        self.scheduler = Scheduler(scheduler_config, cache_config, log_stats)

    def _init_workers(self, distributed_init_method: str):
        # Lazy import the Worker to avoid importing torch.cuda/xformers
        # before CUDA_VISIBLE_DEVICES is set in the Worker
        from vllm.worker.worker import Worker  # pylint: disable=import-outside-toplevel

        assert self.parallel_config.world_size == 1, (
            "Ray is required if parallel_config.world_size > 1.")

        self.workers: List[Worker] = []
        worker = Worker(
            self.model_config,
            self.parallel_config,
            self.scheduler_config,
            0,
            distributed_init_method,
        )
        self.workers.append(worker)
        self._run_workers(
            "init_model",
            get_all_outputs=True,
        )

    def _init_workers_ray(self, placement_group: "PlacementGroup"):
        # Lazy import the Worker to avoid importing torch.cuda/xformers
        # before CUDA_VISIBLE_DEVICES is set in the Worker
        from vllm.worker.worker import Worker  # pylint: disable=import-outside-toplevel

        self.workers: List[Worker] = []
        for bundle in placement_group.bundle_specs:
            if not bundle.get("GPU", 0):
                continue
            worker = ray.remote(
                num_cpus=0,
                num_gpus=1,
                scheduling_strategy=PlacementGroupSchedulingStrategy(
                    placement_group=placement_group,
                    placement_group_capture_child_tasks=True),
            )(RayWorker).remote()
            self.workers.append(worker)

        # Initialize torch distributed process group for the workers.
        init_torch_dist_process_group(self.workers, backend="nccl")
        self._run_workers("init_worker",
                          get_all_outputs=True,
                          worker_init_fn=lambda: Worker(
                              self.model_config,
                              self.parallel_config,
                              self.scheduler_config,
                              None,
                              None,
                          ))
        self._run_workers(
            "init_model",
            get_all_outputs=True,
        )

    def _verify_args(self) -> None:
        self.model_config.verify_with_parallel_config(self.parallel_config)
        self.cache_config.verify_with_parallel_config(self.parallel_config)

    def _init_cache(self) -> None:
        """Profiles the memory usage and initializes the KV cache."""
        # Get the maximum number of blocks that can be allocated on GPU and CPU.
        num_blocks = self._run_workers(
            "profile_num_available_blocks",
            get_all_outputs=True,
            block_size=self.cache_config.block_size,
            gpu_memory_utilization=self.cache_config.gpu_memory_utilization,
            cpu_swap_space=self.cache_config.swap_space_bytes,
        )

        # Since we use a shared centralized controller, we take the minimum
        # number of blocks across all workers to make sure all the memory
        # operators can be applied to all workers.
        num_gpu_blocks = min(b[0] for b in num_blocks)
        num_cpu_blocks = min(b[1] for b in num_blocks)
        # FIXME(woosuk): Change to debug log.
        logger.info(f"# GPU blocks: {num_gpu_blocks}, "
                    f"# CPU blocks: {num_cpu_blocks}")

        if num_gpu_blocks <= 0:
            raise ValueError("No available memory for the cache blocks. "
                             "Try increasing `gpu_memory_utilization` when "
                             "initializing the engine.")

        self.cache_config.num_gpu_blocks = num_gpu_blocks
        self.cache_config.num_cpu_blocks = num_cpu_blocks

        # Initialize the cache.
        self._run_workers("init_cache_engine", cache_config=self.cache_config)

    @classmethod
    def from_engine_args(cls, engine_args: EngineArgs) -> "LLMEngine":
        """Creates an LLM engine from the engine arguments."""
        # Create the engine configs.
        engine_configs = engine_args.create_engine_configs()
        parallel_config = engine_configs[2]
        # Initialize the cluster.
        distributed_init_method, placement_group = initialize_cluster(
            parallel_config)
        # Create the LLM engine.
        engine = cls(*engine_configs,
                     distributed_init_method,
                     placement_group,
                     log_stats=not engine_args.disable_log_stats)
        return engine

    def add_request(
        self,
        request_id: str,
        prompt: Optional[str],
        sampling_params: SamplingParams,
        prompt_token_ids: Optional[List[int]] = None,
        arrival_time: Optional[float] = None,
    ) -> None:
        """Add a request to the engine's request pool.

        The request is added to the request pool and will be processed by the
        scheduler as `engine.step()` is called. The exact scheduling policy is
        determined by the scheduler.

        Args:
            request_id: The unique ID of the request.
            prompt: The prompt string. Can be None if prompt_token_ids is
                provided.
            sampling_params: The sampling parameters for text generation.
            prompt_token_ids: The token IDs of the prompt. If None, we
                use the tokenizer to convert the prompts to token IDs.
            arrival_time: The arrival time of the request. If None, we use
                the current time.
        """
        if arrival_time is None:
            arrival_time = time.time()
        if prompt_token_ids is None:
            assert prompt is not None
            prompt_token_ids = self.tokenizer.encode(prompt)

        # Create the sequences.
        block_size = self.cache_config.block_size
        seqs: List[Sequence] = []
        for _ in range(sampling_params.best_of):
            seq_id = next(self.seq_counter)
            seq = Sequence(seq_id, prompt, prompt_token_ids, block_size)
            seqs.append(seq)

        # Create the sequence group.
        seq_group = SequenceGroup(request_id, seqs, sampling_params,
                                  arrival_time)

        # Add the sequence group to the scheduler.
        self.scheduler.add_seq_group(seq_group)

    def abort_request(self, request_id: str) -> None:
        """Aborts a request with the given ID.

        Args:
            request_id: The ID of the request to abort.
        """
        self.scheduler.abort_seq_group(request_id)

    def get_model_config(self) -> ModelConfig:
        """Gets the model configuration."""
        return self.model_config

    def get_num_unfinished_requests(self) -> int:
        """Gets the number of unfinished requests."""
        return self.scheduler.get_num_unfinished_seq_groups()

    def has_unfinished_requests(self) -> bool:
        """Returns True if there are unfinished requests."""
        return self.scheduler.has_unfinished_seqs()

    def step(self) -> List[RequestOutput]:
        """Performs one decoding iteration and returns newly generated results.

        This function performs one decoding iteration of the engine. It first
        schedules the sequences to be executed in the next iteration and the
        token blocks to be swapped in/out/copy. Then, it executes the model
        and updates the scheduler with the model outputs. Finally, it decodes
        the sequences and returns the newly generated results.
        """
        (seq_group_metadata_list, scheduler_outputs,
         ignored_seq_groups) = self.scheduler.schedule()
        if ((not seq_group_metadata_list) and scheduler_outputs.is_empty()
                and (not ignored_seq_groups)):
            # Nothing to do.
            return []

        # Execute the model.
        output = self._run_workers(
            "execute_model",
            seq_group_metadata_list=seq_group_metadata_list,
            blocks_to_swap_in=scheduler_outputs.blocks_to_swap_in,
            blocks_to_swap_out=scheduler_outputs.blocks_to_swap_out,
            blocks_to_copy=scheduler_outputs.blocks_to_copy,
        )
        # Update the scheduler with the model outputs.
        seq_groups = self.scheduler.update(output)

        # Decode the sequences.
        self._decode_sequences(seq_groups)
        # Stop the sequences that meet the stopping criteria.
        self._stop_sequences(seq_groups)
        # Free the finished sequence groups.
        self.scheduler.free_finished_seq_groups()

        # Create the outputs.
        request_outputs: List[RequestOutput] = []
        for seq_group in seq_groups + ignored_seq_groups:
            request_output = RequestOutput.from_seq_group(seq_group)
            request_outputs.append(request_output)
        return request_outputs

    def _decode_sequences(self, seq_groups: List[SequenceGroup]) -> None:
        """Decodes the sequence outputs."""
        for seq_group in seq_groups:
            for seq in seq_group.get_seqs(status=SequenceStatus.RUNNING):
                new_token, new_output_text = detokenize_incrementally(
                    self.tokenizer,
                    seq.output_tokens,
                    seq.get_last_token_id(),
                    skip_special_tokens=True,
                )
                if new_token is not None:
                    seq.output_tokens.append(new_token)
                    seq.output_text = new_output_text

    def _stop_sequences(self, seq_groups: List[SequenceGroup]) -> None:
        """Stop the finished sequences."""
        for seq_group in seq_groups:
            sampling_params = seq_group.sampling_params
            for seq in seq_group.get_seqs(status=SequenceStatus.RUNNING):
                # Check if the sequence has generated a stop string.
                stopped = False
                for stop_str in sampling_params.stop:
                    if seq.output_text.endswith(stop_str):
                        # Truncate the output text so that the stop string is
                        # not included in the output.
                        seq.output_text = seq.output_text[:-len(stop_str)]
                        self.scheduler.free_seq(
                            seq, SequenceStatus.FINISHED_STOPPED)
                        stopped = True
                        break
                if stopped:
                    continue

                # Check if the sequence has reached max_seq_len.
                if seq.get_len() > self.scheduler_config.max_model_len:
                    self.scheduler.free_seq(
                        seq, SequenceStatus.FINISHED_LENGTH_CAPPED)
                    continue
                # Check if the sequence has reached max_tokens.
                if seq.get_output_len() == sampling_params.max_tokens:
                    self.scheduler.free_seq(
                        seq, SequenceStatus.FINISHED_LENGTH_CAPPED)
                    continue
                # Check if the sequence has generated the EOS token.
                if not sampling_params.ignore_eos:
                    if seq.get_last_token_id() == self.tokenizer.eos_token_id:
                        self.scheduler.free_seq(
                            seq, SequenceStatus.FINISHED_STOPPED)
                        continue

    def _run_workers(
        self,
        method: str,
        *args,
        get_all_outputs: bool = False,
        **kwargs,
    ) -> Any:
        """Runs the given method on all workers."""
        all_outputs = []
        for worker in self.workers:
            if self.parallel_config.worker_use_ray:
                executor = partial(worker.execute_method.remote, method)
            else:
                executor = getattr(worker, method)

            output = executor(*args, **kwargs)
            all_outputs.append(output)

        if self.parallel_config.worker_use_ray:
            all_outputs = ray.get(all_outputs)

        if get_all_outputs:
            return all_outputs

        # Make sure all workers have the same results.
        output = all_outputs[0]
        for other_output in all_outputs[1:]:
            assert output == other_output
        return output