llm_engine.py 75.5 KB
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import time
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from collections import deque
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from contextlib import contextmanager
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from dataclasses import dataclass
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from functools import partial
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from typing import (TYPE_CHECKING, Any, Callable, ClassVar, Deque, Dict,
                    Iterable, List, Mapping, NamedTuple, Optional)
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from typing import Sequence as GenericSequence
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from typing import Set, Type, Union, overload
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import torch
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from typing_extensions import TypeVar
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import vllm.envs as envs
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from vllm.config import (CacheConfig, DecodingConfig, DeviceConfig,
                         EngineConfig, LoadConfig, LoRAConfig, ModelConfig,
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                         ObservabilityConfig, ParallelConfig,
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                         PromptAdapterConfig, SchedulerConfig,
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                         SpeculativeConfig)
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from vllm.core.scheduler import (ScheduledSequenceGroup, Scheduler,
                                 SchedulerOutputs)
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from vllm.engine.arg_utils import EngineArgs
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from vllm.engine.metrics_types import StatLoggerBase, Stats
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from vllm.engine.output_processor.interfaces import (
    SequenceGroupOutputProcessor)
from vllm.engine.output_processor.stop_checker import StopChecker
from vllm.engine.output_processor.util import create_output_by_sequence_group
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from vllm.executor.executor_base import ExecutorBase
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from vllm.executor.gpu_executor import GPUExecutor
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from vllm.executor.ray_utils import initialize_ray_cluster
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from vllm.inputs import (INPUT_REGISTRY, EncoderDecoderLLMInputs,
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                         InputRegistry, LLMInputs, PromptType)
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from vllm.inputs.preprocess import InputPreprocessor
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from vllm.logger import init_logger
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from vllm.lora.request import LoRARequest
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from vllm.model_executor.layers.sampler import SamplerOutput
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from vllm.outputs import (EmbeddingRequestOutput, RequestOutput,
                          RequestOutputFactory)
from vllm.pooling_params import PoolingParams
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from vllm.prompt_adapter.request import PromptAdapterRequest
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from vllm.sampling_params import RequestOutputKind, SamplingParams
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from vllm.sequence import (EmbeddingSequenceGroupOutput, ExecuteModelRequest,
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                           Sequence, SequenceGroup, SequenceGroupMetadata,
                           SequenceStatus)
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from vllm.tracing import (SpanAttributes, SpanKind, extract_trace_context,
                          init_tracer)
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from vllm.transformers_utils.config import try_get_generation_config
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from vllm.transformers_utils.detokenizer import Detokenizer
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from vllm.transformers_utils.tokenizer import AnyTokenizer
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from vllm.transformers_utils.tokenizer_group import (
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    BaseTokenizerGroup, init_tokenizer_from_configs)
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from vllm.usage.usage_lib import (UsageContext, is_usage_stats_enabled,
                                  usage_message)
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from vllm.utils import Counter, Device, deprecate_kwargs, weak_bind
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from vllm.version import __version__ as VLLM_VERSION
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logger = init_logger(__name__)
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_LOCAL_LOGGING_INTERVAL_SEC = 5
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def _load_generation_config_dict(model_config: ModelConfig) -> Dict[str, Any]:
    config = try_get_generation_config(
        model_config.model,
        trust_remote_code=model_config.trust_remote_code,
        revision=model_config.revision,
    )

    if config is None:
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        return {}

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    return config.to_diff_dict()

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_G = TypeVar("_G", bound=BaseTokenizerGroup, default=BaseTokenizerGroup)
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_O = TypeVar("_O", RequestOutput, EmbeddingRequestOutput)


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@dataclass
class SchedulerOutputState:
    """Caches the scheduler outputs for a virtual engine. Used for Multi-Step"""
    seq_group_metadata_list: Optional[List[SequenceGroupMetadata]] = None
    scheduler_outputs: Optional[SchedulerOutputs] = None
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    allow_async_output_proc: bool = False
    last_output: Optional[SamplerOutput] = None
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class OutputData(NamedTuple):
    outputs: List[SamplerOutput]
    seq_group_metadata_list: List[SequenceGroupMetadata]
    scheduler_outputs: SchedulerOutputs
    is_async: bool
    is_last_step: bool
    skip: List[int]


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class SchedulerContext:
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    def __init__(self, multi_step_stream_outputs: bool = False):
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        self.output_queue: Deque[OutputData] = deque()
        self.request_outputs: List[Union[RequestOutput,
                                         EmbeddingRequestOutput]] = []
        self.seq_group_metadata_list: Optional[
            List[SequenceGroupMetadata]] = None
        self.scheduler_outputs: Optional[SchedulerOutputs] = None

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        self.multi_step_stream_outputs: bool = multi_step_stream_outputs

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    def append_output(self, outputs: List[SamplerOutput],
                      seq_group_metadata_list: List[SequenceGroupMetadata],
                      scheduler_outputs: SchedulerOutputs, is_async: bool,
                      is_last_step: bool):
        self.output_queue.append(
            OutputData(outputs=outputs,
                       seq_group_metadata_list=seq_group_metadata_list,
                       scheduler_outputs=scheduler_outputs,
                       is_async=is_async,
                       is_last_step=is_last_step,
                       skip=[]))
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class LLMEngine:
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    """An LLM engine that receives requests and generates texts.
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    This is the main class for the vLLM engine. It receives requests
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    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.

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    The :class:`~vllm.LLM` class wraps this class for offline batched inference
    and the :class:`AsyncLLMEngine` class wraps this class for online serving.
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    The config arguments are derived from :class:`~vllm.EngineArgs`. (See
    :ref:`engine_args`)
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    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.
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        device_config: The configuration related to the device.
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        lora_config (Optional): The configuration related to serving multi-LoRA.
        speculative_config (Optional): The configuration related to speculative
            decoding.
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        executor_class: The model executor class for managing distributed
            execution.
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        prompt_adapter_config (Optional): The configuration related to serving
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            prompt adapters.
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        log_stats: Whether to log statistics.
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        usage_context: Specified entry point, used for usage info collection.
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    """
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    DO_VALIDATE_OUTPUT: ClassVar[bool] = False
    """A flag to toggle whether to validate the type of request output."""

    @classmethod
    @contextmanager
    def enable_output_validation(cls):
        cls.DO_VALIDATE_OUTPUT = True

        yield

        cls.DO_VALIDATE_OUTPUT = False

    @classmethod
    def validate_output(
        cls,
        output: object,
        output_type: Type[_O],
    ) -> _O:
        do_validate = cls.DO_VALIDATE_OUTPUT

        if ((TYPE_CHECKING or do_validate)
                and not isinstance(output, output_type)):
            raise TypeError(f"Expected output of type {output_type}, "
                            f"but found type {type(output)}")

        return output

    @classmethod
    def validate_outputs(
        cls,
        outputs: GenericSequence[object],
        output_type: Type[_O],
    ) -> List[_O]:
        do_validate = cls.DO_VALIDATE_OUTPUT

        outputs_: List[_O]
        if TYPE_CHECKING or do_validate:
            outputs_ = []
            for output in outputs:
                if not isinstance(output, output_type):
                    raise TypeError(f"Expected output of type {output_type}, "
                                    f"but found type {type(output)}")

                outputs_.append(output)
        else:
            outputs_ = outputs

        return outputs_

    tokenizer: Optional[BaseTokenizerGroup]

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    def __init__(
        self,
        model_config: ModelConfig,
        cache_config: CacheConfig,
        parallel_config: ParallelConfig,
        scheduler_config: SchedulerConfig,
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        device_config: DeviceConfig,
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        load_config: LoadConfig,
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        lora_config: Optional[LoRAConfig],
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        speculative_config: Optional[SpeculativeConfig],
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        decoding_config: Optional[DecodingConfig],
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        observability_config: Optional[ObservabilityConfig],
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        prompt_adapter_config: Optional[PromptAdapterConfig],
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        executor_class: Type[ExecutorBase],
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        log_stats: bool,
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        usage_context: UsageContext = UsageContext.ENGINE_CONTEXT,
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        stat_loggers: Optional[Dict[str, StatLoggerBase]] = None,
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        input_registry: InputRegistry = INPUT_REGISTRY,
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        use_cached_outputs: bool = False,
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    ) -> None:
        logger.info(
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            "Initializing an LLM engine (v%s) with config: "
            "model=%r, speculative_config=%r, tokenizer=%r, "
            "skip_tokenizer_init=%s, tokenizer_mode=%s, revision=%s, "
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            "override_neuron_config=%s, "
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            "rope_scaling=%r, rope_theta=%r, tokenizer_revision=%s, "
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            "trust_remote_code=%s, dtype=%s, max_seq_len=%d, "
            "download_dir=%r, load_format=%s, tensor_parallel_size=%d, "
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            "pipeline_parallel_size=%d, "
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            "disable_custom_all_reduce=%s, quantization=%s, "
            "enforce_eager=%s, kv_cache_dtype=%s, "
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            "quantization_param_path=%s, device_config=%s, "
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            "decoding_config=%r, observability_config=%r, "
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            "seed=%d, served_model_name=%s, use_v2_block_manager=%s, "
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            "num_scheduler_steps=%d, multi_step_stream_outputs=%s, "
            "enable_prefix_caching=%s, use_async_output_proc=%s, "
            "use_cached_outputs=%s, mm_processor_kwargs=%s)",
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            VLLM_VERSION,
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            model_config.model,
            speculative_config,
            model_config.tokenizer,
            model_config.skip_tokenizer_init,
            model_config.tokenizer_mode,
            model_config.revision,
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            model_config.override_neuron_config,
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            model_config.rope_scaling,
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            model_config.rope_theta,
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            model_config.tokenizer_revision,
            model_config.trust_remote_code,
            model_config.dtype,
            model_config.max_model_len,
            load_config.download_dir,
            load_config.load_format,
            parallel_config.tensor_parallel_size,
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            parallel_config.pipeline_parallel_size,
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            parallel_config.disable_custom_all_reduce,
            model_config.quantization,
            model_config.enforce_eager,
            cache_config.cache_dtype,
            model_config.quantization_param_path,
            device_config.device,
            decoding_config,
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            observability_config,
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            model_config.seed,
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            model_config.served_model_name,
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            scheduler_config.use_v2_block_manager,
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            scheduler_config.num_scheduler_steps,
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            scheduler_config.multi_step_stream_outputs,
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            cache_config.enable_prefix_caching,
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            model_config.use_async_output_proc,
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            use_cached_outputs,
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            model_config.mm_processor_kwargs,
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        )
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        # TODO(woosuk): Print more configs in debug mode.
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        from vllm.plugins import load_general_plugins
        load_general_plugins()

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        self.model_config = model_config
        self.cache_config = cache_config
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        self.lora_config = lora_config
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        self.parallel_config = parallel_config
        self.scheduler_config = scheduler_config
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        self.device_config = device_config
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        self.speculative_config = speculative_config
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        self.load_config = load_config
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        self.decoding_config = decoding_config or DecodingConfig()
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        self.prompt_adapter_config = prompt_adapter_config
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        self.observability_config = observability_config or ObservabilityConfig(
        )
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        self.log_stats = log_stats
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        self.use_cached_outputs = use_cached_outputs
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        if not self.model_config.skip_tokenizer_init:
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            self.tokenizer = self._init_tokenizer()
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            self.detokenizer = Detokenizer(self.tokenizer)
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            tokenizer_group = self.get_tokenizer_group()
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        else:
            self.tokenizer = None
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            self.detokenizer = None
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            tokenizer_group = None

        # Ensure that the function doesn't contain a reference to self,
        # to avoid engine GC issues
        def get_tokenizer_for_seq(sequence: Sequence) -> AnyTokenizer:
            assert tokenizer_group, ("tokenizer_group cannot be None, "
                                     "make sure skip_tokenizer_init is False")
            return tokenizer_group.get_lora_tokenizer(sequence.lora_request)
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        self.seq_counter = Counter()
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        self.generation_config_fields = _load_generation_config_dict(
            model_config)
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        self.input_preprocessor = InputPreprocessor(model_config,
                                                    self.tokenizer)

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        self.input_registry = input_registry
        self.input_processor = input_registry.create_input_processor(
            model_config)
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        self.model_executor = executor_class(
            model_config=model_config,
            cache_config=cache_config,
            parallel_config=parallel_config,
            scheduler_config=scheduler_config,
            device_config=device_config,
            lora_config=lora_config,
            speculative_config=speculative_config,
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            load_config=load_config,
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            prompt_adapter_config=prompt_adapter_config,
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            observability_config=self.observability_config,
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        )
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        if not self.model_config.embedding_mode:
            self._initialize_kv_caches()
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        # If usage stat is enabled, collect relevant info.
        if is_usage_stats_enabled():
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            from vllm.model_executor.model_loader import (
                get_architecture_class_name)
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            usage_message.report_usage(
                get_architecture_class_name(model_config),
                usage_context,
                extra_kvs={
                    # Common configuration
                    "dtype":
                    str(model_config.dtype),
                    "tensor_parallel_size":
                    parallel_config.tensor_parallel_size,
                    "block_size":
                    cache_config.block_size,
                    "gpu_memory_utilization":
                    cache_config.gpu_memory_utilization,

                    # Quantization
                    "quantization":
                    model_config.quantization,
                    "kv_cache_dtype":
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                    str(cache_config.cache_dtype),
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                    # Feature flags
                    "enable_lora":
                    bool(lora_config),
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                    "enable_prompt_adapter":
                    bool(prompt_adapter_config),
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                    "enable_prefix_caching":
                    cache_config.enable_prefix_caching,
                    "enforce_eager":
                    model_config.enforce_eager,
                    "disable_custom_all_reduce":
                    parallel_config.disable_custom_all_reduce,
                })

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        if self.tokenizer:
            # Ping the tokenizer to ensure liveness if it runs in a
            # different process.
            self.tokenizer.ping()
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        self.cached_scheduler_outputs = [
            SchedulerOutputState()
            for _ in range(self.parallel_config.pipeline_parallel_size)
        ]

        self.scheduler_contexts = [
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            SchedulerContext(multi_step_stream_outputs=self.scheduler_config.
                             multi_step_stream_outputs)
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            for _ in range(self.parallel_config.pipeline_parallel_size)
        ]

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        if model_config.use_async_output_proc:
            process_model_outputs = weak_bind(self._process_model_outputs)

            self.async_callbacks = [
                partial(process_model_outputs,
                        ctx=self.scheduler_contexts[v_id])
                for v_id in range(self.parallel_config.pipeline_parallel_size)
            ]
        else:
            self.async_callbacks = []
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        # Currently used by AsyncLLMEngine to ensure quick append
        # of request outputs to asyncio queues
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        self.process_request_outputs_callback: Optional[Callable] = None
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        # Create the scheduler.
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        # NOTE: the cache_config here have been updated with the numbers of
        # GPU and CPU blocks, which are profiled in the distributed executor.
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        self.scheduler = [
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            Scheduler(
                scheduler_config, cache_config, lora_config,
                parallel_config.pipeline_parallel_size,
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                self.async_callbacks[v_id]
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                if model_config.use_async_output_proc else None)
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            for v_id in range(parallel_config.pipeline_parallel_size)
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        ]
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        # Metric Logging.
        if self.log_stats:
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            if stat_loggers is not None:
                self.stat_loggers = stat_loggers
            else:
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                # Lazy import for prometheus multiprocessing.
                # We need to set PROMETHEUS_MULTIPROC_DIR environment variable
                # before prometheus_client is imported.
                # See https://prometheus.github.io/client_python/multiprocess/
                from vllm.engine.metrics import (LoggingStatLogger,
                                                 PrometheusStatLogger)

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                self.stat_loggers = {
                    "logging":
                    LoggingStatLogger(
                        local_interval=_LOCAL_LOGGING_INTERVAL_SEC),
                    "prometheus":
                    PrometheusStatLogger(
                        local_interval=_LOCAL_LOGGING_INTERVAL_SEC,
                        labels=dict(model_name=model_config.served_model_name),
                        max_model_len=self.model_config.max_model_len),
                }
                self.stat_loggers["prometheus"].info("cache_config",
                                                     self.cache_config)
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        self.tracer = None
        if self.observability_config.otlp_traces_endpoint:
            self.tracer = init_tracer(
                "vllm.llm_engine",
                self.observability_config.otlp_traces_endpoint)

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        # Create sequence output processor, e.g. for beam search or
        # speculative decoding.
        self.output_processor = (
            SequenceGroupOutputProcessor.create_output_processor(
                self.scheduler_config,
                self.detokenizer,
                self.scheduler,
                self.seq_counter,
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                get_tokenizer_for_seq,
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                stop_checker=StopChecker(
                    self.scheduler_config.max_model_len,
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                    get_tokenizer_for_seq,
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                ),
            ))

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    def _initialize_kv_caches(self) -> None:
        """Initialize the KV cache in the worker(s).

        The workers will determine the number of blocks in both the GPU cache
        and the swap CPU cache.
        """
        num_gpu_blocks, num_cpu_blocks = (
            self.model_executor.determine_num_available_blocks())

        if self.cache_config.num_gpu_blocks_override is not None:
            num_gpu_blocks_override = self.cache_config.num_gpu_blocks_override
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            logger.info(
                "Overriding num_gpu_blocks=%d with "
                "num_gpu_blocks_override=%d", num_gpu_blocks,
                num_gpu_blocks_override)
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            num_gpu_blocks = num_gpu_blocks_override

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

        self.model_executor.initialize_cache(num_gpu_blocks, num_cpu_blocks)

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    @classmethod
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    def _get_executor_cls(cls,
                          engine_config: EngineConfig) -> Type[ExecutorBase]:
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        distributed_executor_backend = (
            engine_config.parallel_config.distributed_executor_backend)
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        # Initialize the cluster and specify the executor class.
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        if isinstance(distributed_executor_backend, type):
            if not issubclass(distributed_executor_backend, ExecutorBase):
                raise TypeError(
                    "distributed_executor_backend must be a subclass of "
                    f"ExecutorBase. Got {distributed_executor_backend}.")
            if distributed_executor_backend.uses_ray:  # type: ignore
                initialize_ray_cluster(engine_config.parallel_config)
            executor_class = distributed_executor_backend
        elif engine_config.device_config.device_type == "neuron":
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            from vllm.executor.neuron_executor import NeuronExecutor
            executor_class = NeuronExecutor
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        elif engine_config.device_config.device_type == "tpu":
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            if distributed_executor_backend == "ray":
                initialize_ray_cluster(engine_config.parallel_config)
                from vllm.executor.ray_tpu_executor import RayTPUExecutor
                executor_class = RayTPUExecutor
            else:
                assert distributed_executor_backend is None
                from vllm.executor.tpu_executor import TPUExecutor
                executor_class = TPUExecutor
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        elif engine_config.device_config.device_type == "cpu":
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            from vllm.executor.cpu_executor import CPUExecutor
            executor_class = CPUExecutor
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        elif engine_config.device_config.device_type == "openvino":
            from vllm.executor.openvino_executor import OpenVINOExecutor
            executor_class = OpenVINOExecutor
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        elif engine_config.device_config.device_type == "xpu":
            if distributed_executor_backend == "ray":
                initialize_ray_cluster(engine_config.parallel_config)
                from vllm.executor.ray_xpu_executor import RayXPUExecutor
                executor_class = RayXPUExecutor
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            elif distributed_executor_backend == "mp":
                # FIXME(kunshang):
                # spawn needs calling `if __name__ == '__main__':``
                # fork is not supported for xpu start new process.
                logger.error(
                    "Both start methods (spawn and fork) have issue "
                    "on XPU if you use mp backend, Please try ray instead.")
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            else:
                from vllm.executor.xpu_executor import XPUExecutor
                executor_class = XPUExecutor
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        elif distributed_executor_backend == "ray":
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            initialize_ray_cluster(engine_config.parallel_config)
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            from vllm.executor.ray_gpu_executor import RayGPUExecutor
            executor_class = RayGPUExecutor
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        elif distributed_executor_backend == "mp":
            from vllm.executor.multiproc_gpu_executor import (
                MultiprocessingGPUExecutor)
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            assert not envs.VLLM_USE_RAY_SPMD_WORKER, (
                "multiprocessing distributed executor backend does not "
                "support VLLM_USE_RAY_SPMD_WORKER=1")
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            executor_class = MultiprocessingGPUExecutor
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        else:
            from vllm.executor.gpu_executor import GPUExecutor
            executor_class = GPUExecutor
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        return executor_class

    @classmethod
    def from_engine_args(
        cls,
        engine_args: EngineArgs,
        usage_context: UsageContext = UsageContext.ENGINE_CONTEXT,
        stat_loggers: Optional[Dict[str, StatLoggerBase]] = None,
    ) -> "LLMEngine":
        """Creates an LLM engine from the engine arguments."""
        # Create the engine configs.
        engine_config = engine_args.create_engine_config()
        executor_class = cls._get_executor_cls(engine_config)
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        # Create the LLM engine.
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        engine = cls(
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            **engine_config.to_dict(),
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            executor_class=executor_class,
            log_stats=not engine_args.disable_log_stats,
            usage_context=usage_context,
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            stat_loggers=stat_loggers,
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        )
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        return engine
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    def __reduce__(self):
        # This is to ensure that the LLMEngine is not referenced in
        # the closure used to initialize Ray worker actors
        raise RuntimeError("LLMEngine should not be pickled!")

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    def __del__(self):
        # Shutdown model executor when engine is garbage collected
        # Use getattr since __init__ can fail before the field is set
        if model_executor := getattr(self, "model_executor", None):
            model_executor.shutdown()

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    def get_tokenizer_group(
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        self,
        group_type: Type[_G] = BaseTokenizerGroup,
    ) -> _G:
        tokenizer_group = self.tokenizer

        if tokenizer_group is None:
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            raise ValueError("Unable to get tokenizer because "
                             "skip_tokenizer_init is True")
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        if not isinstance(tokenizer_group, group_type):
            raise TypeError("Invalid type of tokenizer group. "
                            f"Expected type: {group_type}, but "
                            f"found type: {type(tokenizer_group)}")
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        return tokenizer_group
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    def get_tokenizer(
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        self,
        lora_request: Optional[LoRARequest] = None,
    ) -> AnyTokenizer:
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        return self.get_tokenizer_group().get_lora_tokenizer(lora_request)
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    def _init_tokenizer(self) -> BaseTokenizerGroup:
        return init_tokenizer_from_configs(
            model_config=self.model_config,
            scheduler_config=self.scheduler_config,
            parallel_config=self.parallel_config,
            enable_lora=bool(self.lora_config))
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    def _verify_args(self) -> None:
        self.model_config.verify_with_parallel_config(self.parallel_config)
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        self.cache_config.verify_with_parallel_config(self.parallel_config)
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        if self.lora_config:
            self.lora_config.verify_with_model_config(self.model_config)
            self.lora_config.verify_with_scheduler_config(
                self.scheduler_config)
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        if self.prompt_adapter_config:
            self.prompt_adapter_config.verify_with_model_config(
                self.model_config)
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    def _add_processed_request(
        self,
        request_id: str,
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        processed_inputs: Union[LLMInputs, EncoderDecoderLLMInputs],
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        params: Union[SamplingParams, PoolingParams],
        arrival_time: float,
        lora_request: Optional[LoRARequest],
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        prompt_adapter_request: Optional[PromptAdapterRequest],
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        trace_headers: Optional[Mapping[str, str]] = None,
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        priority: int = 0,
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    ) -> None:
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        self._validate_model_inputs(processed_inputs)
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        # Create the sequences.
        block_size = self.cache_config.block_size
        seq_id = next(self.seq_counter)
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        eos_token_id = self.input_preprocessor.get_eos_token_id(lora_request)
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        seq = Sequence(seq_id, processed_inputs, block_size, eos_token_id,
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                       lora_request, prompt_adapter_request)
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        encoder_seq = None
        if 'encoder_prompt_token_ids' in processed_inputs:
            encoder_seq = Sequence(seq_id,
                                   processed_inputs,
                                   block_size,
                                   eos_token_id,
                                   lora_request,
                                   prompt_adapter_request,
                                   from_decoder_prompt=False)

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        # Create a SequenceGroup based on SamplingParams or PoolingParams
        if isinstance(params, SamplingParams):
            seq_group = self._create_sequence_group_with_sampling(
                request_id,
                seq,
                params,
                arrival_time=arrival_time,
                lora_request=lora_request,
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                trace_headers=trace_headers,
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                prompt_adapter_request=prompt_adapter_request,
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                encoder_seq=encoder_seq,
                priority=priority)
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        elif isinstance(params, PoolingParams):
            seq_group = self._create_sequence_group_with_pooling(
                request_id,
                seq,
                params,
                arrival_time=arrival_time,
                lora_request=lora_request,
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                prompt_adapter_request=prompt_adapter_request,
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                encoder_seq=encoder_seq,
                priority=priority)
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        else:
            raise ValueError(
                "Either SamplingParams or PoolingParams must be provided.")

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        # Add the sequence group to the scheduler with least unfinished seqs.
        costs = [
            scheduler.get_num_unfinished_seq_groups()
            for scheduler in self.scheduler
        ]
        min_cost_scheduler = self.scheduler[costs.index(min(costs))]
        min_cost_scheduler.add_seq_group(seq_group)

    def stop_remote_worker_execution_loop(self) -> None:
        self.model_executor.stop_remote_worker_execution_loop()
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    @overload  # DEPRECATED
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    def add_request(
        self,
        request_id: str,
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        *,
        inputs: PromptType,
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        params: Union[SamplingParams, PoolingParams],
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        arrival_time: Optional[float] = None,
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        lora_request: Optional[LoRARequest] = None,
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        trace_headers: Optional[Mapping[str, str]] = None,
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        prompt_adapter_request: Optional[PromptAdapterRequest] = None,
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        priority: int = 0,
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    ) -> None:
        ...

    @overload
    def add_request(
        self,
        request_id: str,
        prompt: PromptType,
        params: Union[SamplingParams, PoolingParams],
        arrival_time: Optional[float] = None,
        lora_request: Optional[LoRARequest] = None,
        trace_headers: Optional[Mapping[str, str]] = None,
        prompt_adapter_request: Optional[PromptAdapterRequest] = None,
        priority: int = 0,
    ) -> None:
        ...

    @deprecate_kwargs(
        "inputs",
        additional_message="Please use the 'prompt' parameter instead.",
    )
    def add_request(
            self,
            request_id: str,
            prompt: Optional[PromptType] = None,
            params: Optional[Union[SamplingParams, PoolingParams]] = None,
            arrival_time: Optional[float] = None,
            lora_request: Optional[LoRARequest] = None,
            trace_headers: Optional[Mapping[str, str]] = None,
            prompt_adapter_request: Optional[PromptAdapterRequest] = None,
            priority: int = 0,
            *,
            inputs: Optional[PromptType] = None,  # DEPRECATED
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    ) -> None:
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        """Add a request to the engine's request pool.
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        The request is added to the request pool and will be processed by the
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        scheduler as `engine.step()` is called. The exact scheduling policy is
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        determined by the scheduler.

        Args:
            request_id: The unique ID of the request.
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            prompt: The prompt to the LLM. See :class:`~vllm.inputs.PromptType`
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                for more details about the format of each input.
            params: Parameters for sampling or pooling.
                :class:`~vllm.SamplingParams` for text generation.
                :class:`~vllm.PoolingParams` for pooling.
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            arrival_time: The arrival time of the request. If None, we use
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                the current monotonic time.
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            trace_headers: OpenTelemetry trace headers.
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            priority: The priority of the request.
                Only applicable with priority scheduling.
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        Details:
            - Set arrival_time to the current time if it is None.
            - Set prompt_token_ids to the encoded prompt if it is None.
            - Create `best_of` number of :class:`~vllm.Sequence` objects.
            - Create a :class:`~vllm.SequenceGroup` object
              from the list of :class:`~vllm.Sequence`.
            - Add the :class:`~vllm.SequenceGroup` object to the scheduler.

        Example:
            >>> # initialize engine
            >>> engine = LLMEngine.from_engine_args(engine_args)
            >>> # set request arguments
            >>> example_prompt = "Who is the president of the United States?"
            >>> sampling_params = SamplingParams(temperature=0.0)
            >>> request_id = 0
            >>>
            >>> # add the request to the engine
            >>> engine.add_request(
            >>>    str(request_id),
            >>>    example_prompt,
            >>>    SamplingParams(temperature=0.0))
            >>> # continue the request processing
            >>> ...
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        """
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        if inputs is not None:
            prompt = inputs
        assert prompt is not None and params is not None

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        if lora_request is not None and not self.lora_config:
            raise ValueError(f"Got lora_request {lora_request} but LoRA is "
                             "not enabled!")
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        if priority > 0 and not self.scheduler_config.policy == "priority":
            raise ValueError(f"Got priority {priority} but "
                             "Priority scheduling is not enabled.")

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        if arrival_time is None:
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            arrival_time = time.time()
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        preprocessed_inputs = self.input_preprocessor.preprocess(
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            prompt,
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            request_id=request_id,
            lora_request=lora_request,
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            prompt_adapter_request=prompt_adapter_request,
        )
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        processed_inputs = self.input_processor(preprocessed_inputs)
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        self._add_processed_request(
            request_id=request_id,
            processed_inputs=processed_inputs,
            params=params,
            arrival_time=arrival_time,
            lora_request=lora_request,
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            prompt_adapter_request=prompt_adapter_request,
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            trace_headers=trace_headers,
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            priority=priority,
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        )
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    def _create_sequence_group_with_sampling(
        self,
        request_id: str,
        seq: Sequence,
        sampling_params: SamplingParams,
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        arrival_time: float,
        lora_request: Optional[LoRARequest],
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        trace_headers: Optional[Mapping[str, str]] = None,
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        prompt_adapter_request: Optional[PromptAdapterRequest] = None,
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        encoder_seq: Optional[Sequence] = None,
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        priority: int = 0,
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    ) -> SequenceGroup:
        """Creates a SequenceGroup with SamplingParams."""
        max_logprobs = self.get_model_config().max_logprobs
        if (sampling_params.logprobs
                and sampling_params.logprobs > max_logprobs) or (
                    sampling_params.prompt_logprobs
                    and sampling_params.prompt_logprobs > max_logprobs):
            raise ValueError(f"Cannot request more than "
                             f"{max_logprobs} logprobs.")

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        # Defensive copy of SamplingParams, which are used by the sampler,
        # this doesn't deep-copy LogitsProcessor objects
        sampling_params = sampling_params.clone()
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        sampling_params.update_from_generation_config(
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            self.generation_config_fields, seq.eos_token_id)
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        # Create the sequence group.
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        seq_group = SequenceGroup(
            request_id=request_id,
            seqs=[seq],
            arrival_time=arrival_time,
            sampling_params=sampling_params,
            lora_request=lora_request,
            trace_headers=trace_headers,
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            prompt_adapter_request=prompt_adapter_request,
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            encoder_seq=encoder_seq,
            priority=priority)
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        return seq_group

    def _create_sequence_group_with_pooling(
        self,
        request_id: str,
        seq: Sequence,
        pooling_params: PoolingParams,
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        arrival_time: float,
        lora_request: Optional[LoRARequest],
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        prompt_adapter_request: Optional[PromptAdapterRequest],
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        encoder_seq: Optional[Sequence] = None,
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        priority: int = 0,
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    ) -> SequenceGroup:
        """Creates a SequenceGroup with PoolingParams."""
        # Defensive copy of PoolingParams, which are used by the pooler
        pooling_params = pooling_params.clone()
        # Create the sequence group.
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        seq_group = SequenceGroup(
            request_id=request_id,
            seqs=[seq],
            arrival_time=arrival_time,
            lora_request=lora_request,
            pooling_params=pooling_params,
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            prompt_adapter_request=prompt_adapter_request,
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            encoder_seq=encoder_seq,
            priority=priority)
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        return seq_group
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    def abort_request(self, request_id: Union[str, Iterable[str]]) -> None:
        """Aborts a request(s) with the given ID.
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        Args:
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            request_id: The ID(s) of the request to abort.
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        Details:
            - Refer to the
              :meth:`~vllm.core.scheduler.Scheduler.abort_seq_group`
              from class :class:`~vllm.core.scheduler.Scheduler`.

        Example:
            >>> # initialize engine and add a request with request_id
            >>> request_id = str(0)
            >>> # abort the request
            >>> engine.abort_request(request_id)
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        """
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        for scheduler in self.scheduler:
            scheduler.abort_seq_group(request_id)
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    def get_model_config(self) -> ModelConfig:
        """Gets the model configuration."""
        return self.model_config

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    def get_parallel_config(self) -> ParallelConfig:
        """Gets the parallel configuration."""
        return self.parallel_config

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    def get_decoding_config(self) -> DecodingConfig:
        """Gets the decoding configuration."""
        return self.decoding_config

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    def get_scheduler_config(self) -> SchedulerConfig:
        """Gets the scheduler configuration."""
        return self.scheduler_config

    def get_lora_config(self) -> LoRAConfig:
        """Gets the LoRA configuration."""
        return self.lora_config

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    def get_num_unfinished_requests(self) -> int:
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        """Gets the number of unfinished requests."""
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        return sum(scheduler.get_num_unfinished_seq_groups()
                   for scheduler in self.scheduler)
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    def has_unfinished_requests(self) -> bool:
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        """Returns True if there are unfinished requests."""
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        return any(scheduler.has_unfinished_seqs()
                   for scheduler in self.scheduler)

    def has_unfinished_requests_for_virtual_engine(
            self, virtual_engine: int) -> bool:
        """
        Returns True if there are unfinished requests for the virtual engine.
        """
        return self.scheduler[virtual_engine].has_unfinished_seqs()
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    @staticmethod
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    def _process_sequence_group_outputs(
        seq_group: SequenceGroup,
        outputs: List[EmbeddingSequenceGroupOutput],
    ) -> None:
        seq_group.embeddings = outputs[0].embeddings

        for seq in seq_group.get_seqs():
            seq.status = SequenceStatus.FINISHED_STOPPED

        return

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    def _process_model_outputs(self,
                               ctx: SchedulerContext,
                               request_id: Optional[str] = None) -> None:
        """Apply the model output to the sequences in the scheduled seq groups
        and return responses.
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        ctx: The virtual engine context to work on
        request_id: If provided, then only this request is going to be processed
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        """
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        now = time.time()
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        if len(ctx.output_queue) == 0:
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            return None

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        # Get pending async postprocessor
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        if request_id:
            # When we process only one request, no pop is required
            # (since later we will process all of the rest)
            (outputs, seq_group_metadata_list, scheduler_outputs, is_async,
             is_last_step, skip) = ctx.output_queue[0]
        else:
            (outputs, seq_group_metadata_list, scheduler_outputs, is_async,
             is_last_step, skip) = ctx.output_queue.popleft()
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        # Sanity check
        assert len(seq_group_metadata_list) == len(
            scheduler_outputs.scheduled_seq_groups)

        # Organize outputs by [step][sequence group] instead of
        # [sequence group][step].
        if len(outputs) > 1:
            outputs_by_sequence_group = create_output_by_sequence_group(
                outputs, num_seq_groups=len(seq_group_metadata_list))
        else:
            outputs_by_sequence_group = outputs

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        # Determine the requests we need to operate on
        if request_id:
            indices = []
            for i, seq_group_meta in enumerate(seq_group_metadata_list):
                if seq_group_meta.request_id == request_id:
                    assert i not in skip  # Cannot be called twice
                    indices.append(i)
                    break

            # If the request_id was not found, then it means that
            # this is a new request that has no pending async
            # postprocessor
            if not indices:
                return
        else:
            indices = range(len(seq_group_metadata_list))  # type: ignore

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        finished_before: List[int] = []
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        finished_now: List[int] = []
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        for i in indices:
            if i in skip:
                continue

            seq_group_meta = seq_group_metadata_list[i]
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            scheduled_seq_group = scheduler_outputs.scheduled_seq_groups[i]
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            seq_group = scheduled_seq_group.seq_group
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            if seq_group.is_finished():
                finished_before.append(i)
                continue

            if len(outputs) > 1:
                output = outputs_by_sequence_group[i]
            else:
                output = [outputs_by_sequence_group[0][i]]

            if not is_async:
                seq_group.update_num_computed_tokens(
                    scheduled_seq_group.token_chunk_size)

            if outputs:
                for o in outputs:
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                    if (isinstance(o, SamplerOutput)
                            and seq_group.metrics is not None):
                        if seq_group.metrics.model_forward_time is not None:
                            seq_group.metrics.model_forward_time += (
                                o.model_forward_time)
                        else:
                            seq_group.metrics.model_forward_time = (
                                o.model_forward_time)
                        if seq_group.metrics.model_execute_time is not None:
                            seq_group.metrics.model_execute_time += (
                                o.model_execute_time)
                        else:
                            seq_group.metrics.model_execute_time = (
                                o.model_execute_time)
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            if self.model_config.embedding_mode:
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                self._process_sequence_group_outputs(seq_group, output)
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            else:
                self.output_processor.process_prompt_logprob(seq_group, output)
                if seq_group_meta.do_sample:
                    self.output_processor.process_outputs(
                        seq_group, output, is_async)
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            if seq_group.is_finished():
                finished_now.append(i)
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        # Generate outputs for the requests that finished this iteration
        for i in finished_now:
            scheduled_seq_group = scheduler_outputs.scheduled_seq_groups[i]
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            seq_group = scheduled_seq_group.seq_group
            seq_group.maybe_set_first_token_time(now)
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            request_output = RequestOutputFactory.create(
                seq_group, use_cache=self.use_cached_outputs)
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            if request_output:
                ctx.request_outputs.append(request_output)
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        # When we process a single request, we skip it for the next time,
        # and invoke the request output callback (if there was final output)
        if request_id:
            assert len(indices) == 1
            skip.append(indices[0])

            if (finished_now
                    and self.process_request_outputs_callback is not None):
                self.process_request_outputs_callback(ctx.request_outputs)
                ctx.request_outputs.clear()
            return

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        # Free currently finished requests
        if finished_now:
            for scheduler in self.scheduler:
                scheduler.free_finished_seq_groups()

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        # For multi-step without streaming, don't create outputs each iteration
        if not is_last_step and not ctx.multi_step_stream_outputs:
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            # Immediately process request outputs here (if callback is given)
            if (finished_now
                    and self.process_request_outputs_callback is not None):
                self.process_request_outputs_callback(ctx.request_outputs)
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                ctx.request_outputs.clear()
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            return

        # Create the outputs
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        for i in indices:
            if i in skip or i in finished_before or i in finished_now:
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                continue  # Avoids double processing

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            scheduled_seq_group = scheduler_outputs.scheduled_seq_groups[i]

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            seq_group = scheduled_seq_group.seq_group
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            seq_group.maybe_set_first_token_time(now)
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            request_output = RequestOutputFactory.create(
                seq_group, use_cache=self.use_cached_outputs)
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            if request_output:
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                ctx.request_outputs.append(request_output)
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        # For multi-step with streaming, create outputs each iteration
        if not is_last_step and ctx.multi_step_stream_outputs:
            # Immediately process request outputs here (if callback is given)
            if self.process_request_outputs_callback is not None:
                self.process_request_outputs_callback(ctx.request_outputs)
                ctx.request_outputs.clear()
            return

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        for seq_group in scheduler_outputs.ignored_seq_groups:
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            params = seq_group.sampling_params
            if params is not None and params.output_kind == (
                    RequestOutputKind.DELTA) and not seq_group.is_finished():
                continue

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            request_output = RequestOutputFactory.create(
                seq_group, use_cache=self.use_cached_outputs)
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            if request_output:
                ctx.request_outputs.append(request_output)
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        # Immediately process request outputs here (if callback is given)
        if (ctx.request_outputs
                and self.process_request_outputs_callback is not None):
            self.process_request_outputs_callback(ctx.request_outputs)
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            ctx.request_outputs.clear()
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        # For async case, we need to record the stats here.
        # For non-async case, the stats are done in the
        # LLMEngine/AsyncLLMEngine directly
        if is_async:
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            # Log stats.
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            self.do_log_stats(scheduler_outputs, outputs, finished_before,
                              skip)
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            # Tracing
            self.do_tracing(scheduler_outputs)

        return None

    def _advance_to_next_step(
            self, output: List[SamplerOutput],
            seq_group_metadata_list: List[SequenceGroupMetadata],
            scheduled_seq_groups: List[ScheduledSequenceGroup]) -> None:
        """Given model output from a single run, append the tokens to the
        sequences. This is normally done inside output processor, but it is
        required if the worker is to perform async forward pass to next step.
        """
        for seq_group_metadata, sequence_group_outputs, scheduled_seq_group in \
            zip(seq_group_metadata_list, output, scheduled_seq_groups):
            seq_group = scheduled_seq_group.seq_group

            if seq_group.is_finished():
                continue

            seq_group.update_num_computed_tokens(
                seq_group_metadata.token_chunk_size)

            if seq_group_metadata.do_sample:
                assert len(sequence_group_outputs.samples) == 1, (
                    "Async output processor expects a single sample"
                    " (i.e sampling_params.n == 1 and no "
                    "sampling_params.best_of > 1)")
                sample = sequence_group_outputs.samples[0]

                assert len(seq_group.seqs) == 1
                seq = seq_group.seqs[0]
                seq.append_token_id(sample.output_token, sample.logprobs)
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    def step(self) -> List[Union[RequestOutput, EmbeddingRequestOutput]]:
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        """Performs one decoding iteration and returns newly generated results.

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        .. figure:: https://i.imgur.com/sv2HssD.png
            :alt: Overview of the step function
            :align: center

            Overview of the step function.

        Details:
            - Step 1: Schedules the sequences to be executed in the next
              iteration and the token blocks to be swapped in/out/copy.

                - Depending on the scheduling policy,
                  sequences may be `preempted/reordered`.
                - A Sequence Group (SG) refer to a group of sequences
                  that are generated from the same prompt.

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            - Step 2: Calls the distributed executor to execute the model.
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            - Step 3: Processes the model output. This mainly includes:

                - Decodes the relevant outputs.
                - Updates the scheduled sequence groups with model outputs
                  based on its `sampling parameters` (`use_beam_search` or not).
                - Frees the finished sequence groups.

            - Finally, it creates and returns the newly generated results.

        Example:
            >>> # Please see the example/ folder for more detailed examples.
            >>>
            >>> # initialize engine and request arguments
            >>> engine = LLMEngine.from_engine_args(engine_args)
            >>> example_inputs = [(0, "What is LLM?",
            >>>    SamplingParams(temperature=0.0))]
            >>>
            >>> # Start the engine with an event loop
            >>> while True:
            >>>     if example_inputs:
            >>>         req_id, prompt, sampling_params = example_inputs.pop(0)
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            >>>         engine.add_request(str(req_id),prompt,sampling_params)
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            >>>
            >>>     # continue the request processing
            >>>     request_outputs = engine.step()
            >>>     for request_output in request_outputs:
            >>>         if request_output.finished:
            >>>             # return or show the request output
            >>>
            >>>     if not (engine.has_unfinished_requests() or example_inputs):
            >>>         break
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        """
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        if self.parallel_config.pipeline_parallel_size > 1:
            raise NotImplementedError(
                "Pipeline parallelism is only supported through AsyncLLMEngine "
                "as performance will be severely degraded otherwise.")
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        # For llm_engine, there is no pipeline parallel support, so the engine
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        # used is always 0.
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        virtual_engine = 0

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        # These are cached outputs from previous iterations. None if on first
        # iteration
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        cached_outputs = self.cached_scheduler_outputs[virtual_engine]
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        seq_group_metadata_list = cached_outputs.seq_group_metadata_list
        scheduler_outputs = cached_outputs.scheduler_outputs
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        allow_async_output_proc = cached_outputs.allow_async_output_proc
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        ctx = self.scheduler_contexts[virtual_engine]

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        # Clear outputs for each new scheduler iteration
        ctx.request_outputs.clear()

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        # Skip the scheduler if there are any remaining steps in the seq groups.
        # This ensures that the scheduler is only called again when the current
        # batch has completed.
        if not self._has_remaining_steps(seq_group_metadata_list):
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            # Schedule iteration
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            (seq_group_metadata_list, scheduler_outputs,
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             allow_async_output_proc
             ) = self.scheduler[virtual_engine].schedule()
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            ctx.seq_group_metadata_list = seq_group_metadata_list
            ctx.scheduler_outputs = scheduler_outputs
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            # Maybe switch from async mode to sync mode
            if not allow_async_output_proc and len(ctx.output_queue) > 0:
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                self._process_model_outputs(ctx=ctx)
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            if (self.scheduler_config.is_multi_step
                    and scheduler_outputs.num_lookahead_slots > 0):
                # cache the scheduler outputs for the next iteration if we have
                # lookahead slots
                self._cache_scheduler_outputs_for_multi_step(
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                    virtual_engine, seq_group_metadata_list, scheduler_outputs,
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                    allow_async_output_proc)
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        assert seq_group_metadata_list is not None
        assert scheduler_outputs is not None
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        if not scheduler_outputs.is_empty():
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            finished_requests_ids = self.scheduler[
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                virtual_engine].get_and_reset_finished_requests_ids()
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            # Check if we have a cached last_output from the previous iteration.
            # For supporting PP this is probably the best way to pass the
            # sampled_token_ids, as a separate broadcast over all the PP stages
            # will cause one virtual engine's microbatch to block the pipeline.
            last_sampled_token_ids = \
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                self._get_last_sampled_token_ids(virtual_engine)
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            execute_model_req = ExecuteModelRequest(
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                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,
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                num_lookahead_slots=scheduler_outputs.num_lookahead_slots,
                running_queue_size=scheduler_outputs.running_queue_size,
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                finished_requests_ids=finished_requests_ids,
                # We use ExecuteModelRequest to pass the last sampled_token_ids
                # to each of the non-last PP stages for in-place prepare_input.
                last_sampled_token_ids=last_sampled_token_ids)

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            if allow_async_output_proc:
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                execute_model_req.async_callback = self.async_callbacks[
                    virtual_engine]
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            outputs = self.model_executor.execute_model(
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                execute_model_req=execute_model_req)
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            # We need to do this here so that last step's sampled_token_ids can
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            # be passed to the next iteration for PP.
            if self.scheduler_config.is_multi_step:
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                self._update_cached_scheduler_output(virtual_engine, outputs)
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        else:
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            # Nothing scheduled => If there is pending async postprocessor,
            # then finish it here.
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            if len(ctx.output_queue) > 0:
                self._process_model_outputs(ctx=ctx)
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            # No outputs in this case
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            outputs = []
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        # Finish the current step for all the sequence groups.
        if self.scheduler_config.is_multi_step:
            for seq_group in seq_group_metadata_list:
                seq_group.finish_step()

        if not self._has_remaining_steps(seq_group_metadata_list):
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            # clear the cache if we have finished all the steps.
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            if self.scheduler_config.is_multi_step:
                self.cached_scheduler_outputs[0] = SchedulerOutputState()

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            # Add results to the output_queue
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            ctx.append_output(outputs=outputs,
                              seq_group_metadata_list=seq_group_metadata_list,
                              scheduler_outputs=scheduler_outputs,
                              is_async=allow_async_output_proc,
                              is_last_step=True)

            if outputs and allow_async_output_proc:
                assert len(outputs) == 1, (
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                    "Async postprocessor expects only a single output set")
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                self._advance_to_next_step(
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                    outputs[0], seq_group_metadata_list,
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                    scheduler_outputs.scheduled_seq_groups)
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            # Check if need to run the usual non-async path
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            if not allow_async_output_proc:
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                self._process_model_outputs(ctx=ctx)
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                # Log stats.
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                self.do_log_stats(scheduler_outputs, outputs)
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                # Tracing
                self.do_tracing(scheduler_outputs)
        else:
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            # Multi-step case
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            return ctx.request_outputs
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        if not self.has_unfinished_requests():
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            # Drain async postprocessor (if exists)
            if len(ctx.output_queue) > 0:
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                self._process_model_outputs(ctx=ctx)
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            assert len(ctx.output_queue) == 0
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            # Stop the execute model loop in parallel workers until there are
            # more requests to process. This avoids waiting indefinitely in
            # torch.distributed ops which may otherwise timeout, and unblocks
            # the RPC thread in the workers so that they can process any other
            # queued control plane messages, such as add/remove lora adapters.
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            logger.debug("Stopping remote worker execution loop.")
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            self.model_executor.stop_remote_worker_execution_loop()

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        return ctx.request_outputs
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    def _has_remaining_steps(
        self, seq_group_metadata_list: Optional[List[SequenceGroupMetadata]]
    ) -> bool:
        if (not self.scheduler_config.is_multi_step
                or not seq_group_metadata_list):
            return False

        # TODO(will) this is a sanity check for nowto make sure that all the
        # seqs are on the same steps. Eventually we will want to do some sort of
        # dynamic scheduling when doing multi-step decoding.
        ref_remaining_steps = seq_group_metadata_list[0].state.remaining_steps
        if any([
                seq_group.state.remaining_steps != ref_remaining_steps
                for seq_group in seq_group_metadata_list[1:]
        ]):
            raise AssertionError(("All running sequence groups should "
                                  "have the same remaining steps."))

        return ref_remaining_steps > 0

    def _cache_scheduler_outputs_for_multi_step(
            self, virtual_engine: int,
            seq_group_metadata_list: Optional[List[SequenceGroupMetadata]],
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            scheduler_outputs: SchedulerOutputs,
            allow_async_output_proc: bool) -> None:
        co = self.cached_scheduler_outputs[virtual_engine]

        co.seq_group_metadata_list = seq_group_metadata_list
        co.scheduler_outputs = scheduler_outputs
        co.allow_async_output_proc = allow_async_output_proc
        co.last_output = None
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    def _update_cached_scheduler_output(
            self, virtual_engine: int,
            output: List[Optional[SamplerOutput]]) -> None:
        if (self.parallel_config.pipeline_parallel_size > 1 and len(output) > 0
                and output[0] is not None):
            last_output = output[-1]
            assert last_output is not None
            assert last_output.sampled_token_ids_cpu is not None
            assert last_output.sampled_token_ids is None
            assert last_output.sampled_token_probs is None
            self.cached_scheduler_outputs[
                virtual_engine].last_output = last_output

    def _get_last_sampled_token_ids(
            self, virtual_engine: int) -> Optional[torch.Tensor]:
        cached_last_output = self.cached_scheduler_outputs[
            virtual_engine].last_output
        if (self.scheduler_config.is_multi_step
                and self.parallel_config.pipeline_parallel_size > 1
                and cached_last_output is not None
                and cached_last_output.sampled_token_ids_cpu is not None):
            return cached_last_output.sampled_token_ids_cpu
        return None

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    def add_logger(self, logger_name: str, logger: StatLoggerBase) -> None:
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        if not self.log_stats:
            raise RuntimeError(
                "Stat logging is disabled. Set `disable_log_stats=False` "
                "argument to enable.")
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        if logger_name in self.stat_loggers:
            raise KeyError(f"Logger with name {logger_name} already exists.")
        self.stat_loggers[logger_name] = logger

    def remove_logger(self, logger_name: str) -> None:
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        if not self.log_stats:
            raise RuntimeError(
                "Stat logging is disabled. Set `disable_log_stats=False` "
                "argument to enable.")
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        if logger_name not in self.stat_loggers:
            raise KeyError(f"Logger with name {logger_name} does not exist.")
        del self.stat_loggers[logger_name]

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    def do_log_stats(self,
                     scheduler_outputs: Optional[SchedulerOutputs] = None,
                     model_output: Optional[List[SamplerOutput]] = None,
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                     finished_before: Optional[List[int]] = None,
                     skip: Optional[List[int]] = None) -> None:
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        """Forced log when no requests active."""
        if self.log_stats:
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            stats = self._get_stats(scheduler_outputs, model_output,
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                                    finished_before, skip)
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            for logger in self.stat_loggers.values():
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                logger.log(stats)
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    def _get_stats(self,
                   scheduler_outputs: Optional[SchedulerOutputs],
                   model_output: Optional[List[SamplerOutput]] = None,
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                   finished_before: Optional[List[int]] = None,
                   skip: Optional[List[int]] = None) -> Stats:
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        """Get Stats to be Logged to Prometheus.

        Args:
            scheduler_outputs: Optional, used to populate metrics related to
                the scheduled batch,
            model_output: Optional, used to emit speculative decoding metrics
                which are created by the workers.
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            finished_before: Optional, indices of sequences that were finished
                before. These sequences will be ignored.
            skip: Optional, indices of sequences that were preempted. These
                sequences will be ignored.
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        """
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        now = time.time()
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        # System State
        #   Scheduler State
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        num_running_sys = sum(
            len(scheduler.running) for scheduler in self.scheduler)
        num_swapped_sys = sum(
            len(scheduler.swapped) for scheduler in self.scheduler)
        num_waiting_sys = sum(
            len(scheduler.waiting) for scheduler in self.scheduler)
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        # KV Cache Usage in %
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        num_total_gpu = self.cache_config.num_gpu_blocks
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        gpu_cache_usage_sys = 0.
        if num_total_gpu is not None:
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            num_free_gpu = sum(
                scheduler.block_manager.get_num_free_gpu_blocks()
                for scheduler in self.scheduler)
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            gpu_cache_usage_sys = 1.0 - (num_free_gpu / num_total_gpu)
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        num_total_cpu = self.cache_config.num_cpu_blocks
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        cpu_cache_usage_sys = 0.
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        if num_total_cpu is not None and num_total_cpu > 0:
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            num_free_cpu = sum(
                scheduler.block_manager.get_num_free_cpu_blocks()
                for scheduler in self.scheduler)
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            cpu_cache_usage_sys = 1.0 - (num_free_cpu / num_total_cpu)

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        # Prefix Cache Hit Rate. Note that we always use
        # the cache hit rate of the first virtual engine.
        cpu_prefix_cache_hit_rate = self.scheduler[
            0].get_prefix_cache_hit_rate(Device.CPU)
        gpu_prefix_cache_hit_rate = self.scheduler[
            0].get_prefix_cache_hit_rate(Device.GPU)

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        # Iteration stats
        num_prompt_tokens_iter = 0
        num_generation_tokens_iter = 0
        time_to_first_tokens_iter: List[float] = []
        time_per_output_tokens_iter: List[float] = []
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        num_preemption_iter = (0 if scheduler_outputs is None else
                               scheduler_outputs.preempted)
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        # Request stats
        #   Latency
        time_e2e_requests: List[float] = []
        #   Metadata
        num_prompt_tokens_requests: List[int] = []
        num_generation_tokens_requests: List[int] = []
        best_of_requests: List[int] = []
        n_requests: List[int] = []
        finished_reason_requests: List[str] = []

        # NOTE: This loop assumes prefill seq_groups are before
        # decode seq_groups in scheduled_seq_groups.
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        if scheduler_outputs is not None:
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            # For async postprocessor, already finished sequences need to be
            # not counted (to avoid double counting)
            actual_num_batched_tokens = scheduler_outputs.num_batched_tokens  # type: ignore

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            num_generation_tokens_from_prefill_groups = 0.
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            # NOTE: if scheduler_outputs.num_prefill_groups > 0 and
            # the len of scheduler_outputs.scheduled_seq_groups is !=
            # scheduler_outputs.num_prefill_groups, this means that
            # chunked prefills have been detected.
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            for idx, scheduled_seq_group in enumerate(
                    scheduler_outputs.scheduled_seq_groups):
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                # Skip double logging when using async output proc
                if finished_before and idx in finished_before:
                    actual_num_batched_tokens -= 1
                    continue
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                # Currently, skip == preempted sequences, so we need to skip
                # their log stats
                if skip and idx in skip:
                    continue
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                group_was_prefill = idx < scheduler_outputs.num_prefill_groups
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                seq_group = scheduled_seq_group.seq_group
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                # NOTE: a seq_group that completed all of its prefill tokens
                # in the last iteration will have seq_group.is_prefill() = False
                # with group_was_prefill = True
                if group_was_prefill:
                    # Number of prompt tokens.
                    num_prompt_tokens_iter += (
                        scheduled_seq_group.token_chunk_size)

                    # If the seq_group just finished the prefill state
                    # get TTFT.
                    if not seq_group.is_prefill():
                        latency = seq_group.get_last_latency(now)
                        time_to_first_tokens_iter.append(latency)

                        # One generation token per finished prefill.
                        num_generation_tokens_from_prefill_groups += (
                            seq_group.num_seqs())
                else:
                    # TPOTs.
                    latency = seq_group.get_last_latency(now)
                    time_per_output_tokens_iter.append(latency)

                # Because of chunked prefill, we can have a single sequence
                # group that does multiple prompt_runs. To prevent logging
                # the same metadata more than once per request, we standardize
                # on logging request level information for finished requests,
                # which can only happen once.
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                if seq_group.is_finished():
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                    # Latency timings
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                    time_e2e_requests.append(now -
                                             seq_group.metrics.arrival_time)
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                    # Metadata
                    num_prompt_tokens_requests.append(
                        len(seq_group.prompt_token_ids))
                    num_generation_tokens_requests.extend([
                        seq.get_output_len()
                        for seq in seq_group.get_finished_seqs()
                    ])
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                    if seq_group.sampling_params is not None:
                        best_of_requests.append(
                            seq_group.sampling_params.best_of)
                        n_requests.append(seq_group.sampling_params.n)
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                    finished_reason_requests.extend([
                        SequenceStatus.get_finished_reason(seq.status)
                        for seq in seq_group.get_finished_seqs()
                    ])

            # Number of generation tokens.
            #   num_batched_tokens equals the number of prompt_tokens plus the
            #   number of decode_tokens in a single iteration. So,
            #   num_generation_tokens = num_batched_tokens - num_prompt_tokens
            #   + num_generation_tokens_from_prefill_groups (since we generate
            #   one token on prefills on iters where the prefill finishes).
            num_generation_tokens_iter = (
1609
                actual_num_batched_tokens - num_prompt_tokens_iter +
1610
                num_generation_tokens_from_prefill_groups)
1611

1612
1613
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1615
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1617
1618
1619
        # Spec decode, if enabled, emits specialized metrics from the worker in
        # sampler output.
        if model_output and (model_output[0].spec_decode_worker_metrics
                             is not None):
            spec_decode_metrics = model_output[0].spec_decode_worker_metrics
        else:
            spec_decode_metrics = None

1620
1621
        return Stats(
            now=now,
1622
1623
1624
1625
1626
1627
1628
1629
            # System stats
            #   Scheduler State
            num_running_sys=num_running_sys,
            num_swapped_sys=num_swapped_sys,
            num_waiting_sys=num_waiting_sys,
            #   KV Cache Usage in %
            gpu_cache_usage_sys=gpu_cache_usage_sys,
            cpu_cache_usage_sys=cpu_cache_usage_sys,
1630
1631
1632
            #   Prefix Cache Hit Rate
            cpu_prefix_cache_hit_rate=cpu_prefix_cache_hit_rate,
            gpu_prefix_cache_hit_rate=gpu_prefix_cache_hit_rate,
1633
1634
1635
1636
1637
1638

            # Iteration stats
            num_prompt_tokens_iter=num_prompt_tokens_iter,
            num_generation_tokens_iter=num_generation_tokens_iter,
            time_to_first_tokens_iter=time_to_first_tokens_iter,
            time_per_output_tokens_iter=time_per_output_tokens_iter,
1639
            spec_decode_metrics=spec_decode_metrics,
1640
            num_preemption_iter=num_preemption_iter,
1641
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1643
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1645
1646
1647
1648
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1650

            # Request stats
            #   Latency
            time_e2e_requests=time_e2e_requests,
            #   Metadata
            num_prompt_tokens_requests=num_prompt_tokens_requests,
            num_generation_tokens_requests=num_generation_tokens_requests,
            best_of_requests=best_of_requests,
            n_requests=n_requests,
            finished_reason_requests=finished_reason_requests,
1651
1652
        )

1653
    def add_lora(self, lora_request: LoRARequest) -> bool:
1654
        return self.model_executor.add_lora(lora_request)
1655
1656

    def remove_lora(self, lora_id: int) -> bool:
1657
        return self.model_executor.remove_lora(lora_id)
1658

1659
    def list_loras(self) -> Set[int]:
1660
        return self.model_executor.list_loras()
1661

1662
1663
1664
    def pin_lora(self, lora_id: int) -> bool:
        return self.model_executor.pin_lora(lora_id)

1665
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1668
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1674
    def add_prompt_adapter(
            self, prompt_adapter_request: PromptAdapterRequest) -> bool:
        return self.model_executor.add_prompt_adapter(prompt_adapter_request)

    def remove_prompt_adapter(self, prompt_adapter_id: int) -> bool:
        return self.model_executor.remove_prompt_adapter(prompt_adapter_id)

    def list_prompt_adapters(self) -> List[int]:
        return self.model_executor.list_prompt_adapters()

1675
    def check_health(self) -> None:
1676
1677
        if self.tokenizer:
            self.tokenizer.check_health()
1678
        self.model_executor.check_health()
1679

1680
    def start_profile(self) -> None:
1681
1682
        # using type instead of isinstance to check to avoid capturing
        # inherited classes (MultiprocessingGPUExecutor)
1683
        if type(self.model_executor) == GPUExecutor:  # noqa: E721
1684
1685
1686
            self.model_executor.start_profile()
        else:
            self.model_executor._run_workers("start_profile")
1687
1688

    def stop_profile(self) -> None:
1689
1690
        # using type instead of isinstance to check to avoid capturing
        # inherited classes (MultiprocessingGPUExecutor)
1691
        if type(self.model_executor) == GPUExecutor:  # noqa: E721
1692
1693
1694
            self.model_executor.stop_profile()
        else:
            self.model_executor._run_workers("stop_profile")
1695

1696
1697
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1701
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1753
    def is_tracing_enabled(self) -> bool:
        return self.tracer is not None

    def do_tracing(self, scheduler_outputs: SchedulerOutputs) -> None:
        if self.tracer is None:
            return

        for scheduled_seq_group in scheduler_outputs.scheduled_seq_groups:
            seq_group = scheduled_seq_group.seq_group
            if seq_group.is_finished():
                self.create_trace_span(seq_group)

    def create_trace_span(self, seq_group: SequenceGroup) -> None:
        if self.tracer is None or seq_group.sampling_params is None:
            return
        arrival_time_nano_seconds = int(seq_group.metrics.arrival_time * 1e9)

        trace_context = extract_trace_context(seq_group.trace_headers)

        with self.tracer.start_as_current_span(
                "llm_request",
                kind=SpanKind.SERVER,
                context=trace_context,
                start_time=arrival_time_nano_seconds) as seq_span:
            metrics = seq_group.metrics
            ttft = metrics.first_token_time - metrics.arrival_time
            e2e_time = metrics.finished_time - metrics.arrival_time
            # attribute names are based on
            # https://github.com/open-telemetry/semantic-conventions/blob/main/docs/gen-ai/llm-spans.md
            seq_span.set_attribute(SpanAttributes.LLM_RESPONSE_MODEL,
                                   self.model_config.model)
            seq_span.set_attribute(SpanAttributes.LLM_REQUEST_ID,
                                   seq_group.request_id)
            seq_span.set_attribute(SpanAttributes.LLM_REQUEST_TEMPERATURE,
                                   seq_group.sampling_params.temperature)
            seq_span.set_attribute(SpanAttributes.LLM_REQUEST_TOP_P,
                                   seq_group.sampling_params.top_p)
            seq_span.set_attribute(SpanAttributes.LLM_REQUEST_MAX_TOKENS,
                                   seq_group.sampling_params.max_tokens)
            seq_span.set_attribute(SpanAttributes.LLM_REQUEST_BEST_OF,
                                   seq_group.sampling_params.best_of)
            seq_span.set_attribute(SpanAttributes.LLM_REQUEST_N,
                                   seq_group.sampling_params.n)
            seq_span.set_attribute(SpanAttributes.LLM_USAGE_NUM_SEQUENCES,
                                   seq_group.num_seqs())
            seq_span.set_attribute(SpanAttributes.LLM_USAGE_PROMPT_TOKENS,
                                   len(seq_group.prompt_token_ids))
            seq_span.set_attribute(
                SpanAttributes.LLM_USAGE_COMPLETION_TOKENS,
                sum([
                    seq.get_output_len()
                    for seq in seq_group.get_finished_seqs()
                ]))
            seq_span.set_attribute(SpanAttributes.LLM_LATENCY_TIME_IN_QUEUE,
                                   metrics.time_in_queue)
            seq_span.set_attribute(
                SpanAttributes.LLM_LATENCY_TIME_TO_FIRST_TOKEN, ttft)
            seq_span.set_attribute(SpanAttributes.LLM_LATENCY_E2E, e2e_time)
1754
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1760
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1765
            if metrics.scheduler_time is not None:
                seq_span.set_attribute(
                    SpanAttributes.LLM_LATENCY_TIME_IN_SCHEDULER,
                    metrics.scheduler_time)
            if metrics.model_forward_time is not None:
                seq_span.set_attribute(
                    SpanAttributes.LLM_LATENCY_TIME_IN_MODEL_FORWARD,
                    metrics.model_forward_time / 1000.0)
            if metrics.model_execute_time is not None:
                seq_span.set_attribute(
                    SpanAttributes.LLM_LATENCY_TIME_IN_MODEL_EXECUTE,
                    metrics.model_execute_time)
1766
1767

    def is_encoder_decoder_model(self):
1768
        return self.input_preprocessor.is_encoder_decoder_model()
1769
1770

    def is_embedding_model(self):
1771
        return self.model_config.is_embedding_model
1772
1773
1774

    def _validate_model_inputs(self, inputs: Union[LLMInputs,
                                                   EncoderDecoderLLMInputs]):
1775
1776
1777
1778
1779
1780
        if self.is_encoder_decoder_model():
            prompt_ids = inputs.get("encoder_prompt_token_ids")
        else:
            prompt_ids = inputs.get("prompt_token_ids")

        if prompt_ids is None or len(prompt_ids) == 0:
1781
            raise ValueError("Prompt cannot be empty")
1782

1783
        if self.model_config.is_multimodal_model:
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
            max_prompt_len = self.model_config.max_model_len

            if len(prompt_ids) > max_prompt_len:
                raise ValueError(
                    f"The prompt (total length {len(prompt_ids)}) is too long "
                    f"to fit into the model (context length {max_prompt_len}). "
                    "Make sure that `max_model_len` is no smaller than the "
                    "number of text tokens plus multimodal tokens. For image "
                    "inputs, the number of image tokens depends on the number "
                    "of images, and possibly their aspect ratios as well.")
1794
1795
1796
1797

            # TODO: Find out how many placeholder tokens are there so we can
            # check that chunked prefill does not truncate them
            # max_batch_len = self.scheduler_config.max_num_batched_tokens