[Frontend] Reduce vLLM's import time

This change optimizes the import time of `import vllm` and contributes to
#14924. Most of the changes are to lazily instead of eagerly import expensive
modules. This change shouldn't affect core functionality.

Co-authored-by: Chen-0210 <chenjincong11@gmail.com>
Co-authored-by: David Xia <david@davidxia.com>

Signed-off-by: Chen-0210 <chenjincong11@gmail.com>
Signed-off-by: David Xia <david@davidxia.com>

Author: Chen-0210

vllm/config.py

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
+from __future__ import annotations
+
 import ast
 import copy
 import enum
@@ -22,42 +24,45 @@
 import torch
 from pydantic import BaseModel, Field, PrivateAttr
 from torch.distributed import ProcessGroup, ReduceOp
-from transformers import PretrainedConfig
 
 import vllm.envs as envs
 from vllm.compilation.inductor_pass import CallableInductorPass, InductorPass
 from vllm.logger import init_logger
-from vllm.model_executor.layers.quantization import (QUANTIZATION_METHODS,
-                                                     get_quantization_config)
-from vllm.model_executor.models import ModelRegistry
-from vllm.platforms import CpuArchEnum, current_platform
+from vllm.platforms import CpuArchEnum
 from vllm.sampling_params import GuidedDecodingParams
-from vllm.tracing import is_otel_available, otel_import_error_traceback
 from vllm.transformers_utils.config import (
     ConfigFormat, get_config, get_hf_image_processor_config,
     get_hf_text_config, get_pooling_config,
     get_sentence_transformer_tokenizer_config, is_encoder_decoder,
     try_get_generation_config, uses_mrope)
 from vllm.transformers_utils.s3_utils import S3Model
 from vllm.transformers_utils.utils import is_s3, maybe_model_redirect
-from vllm.utils import (GiB_bytes, LayerBlockType, cuda_device_count_stateless,
-                        get_cpu_memory, get_open_port, is_torch_equal_or_newer,
-                        random_uuid, resolve_obj_by_qualname)
+from vllm.utils import (GiB_bytes, LayerBlockType, LazyLoader,
+                        cuda_device_count_stateless, get_cpu_memory,
+                        get_open_port, is_torch_equal_or_newer, random_uuid,
+                        resolve_obj_by_qualname)
 
 if TYPE_CHECKING:
     from _typeshed import DataclassInstance
     from ray.util.placement_group import PlacementGroup
+    from transformers import PretrainedConfig
 
     from vllm.executor.executor_base import ExecutorBase
     from vllm.model_executor.layers.quantization.base_config import (
         QuantizationConfig)
     from vllm.model_executor.model_loader.loader import BaseModelLoader
 
     ConfigType = type[DataclassInstance]
+    HfOverrides = Union[dict[str, Any], Callable[[PretrainedConfig],
+                                                 PretrainedConfig]]
 else:
-    QuantizationConfig = None
+    HfOverrides = None
     ConfigType = type
 
+me_quant = LazyLoader("model_executor", globals(),
+                      "vllm.model_executor.layers.quantization")
+me_models = LazyLoader("model_executor", globals(),
+                       "vllm.model_executor.models")
 logger = init_logger(__name__)
 
 ConfigT = TypeVar("ConfigT", bound=ConfigType)
@@ -89,9 +94,6 @@
     for task in tasks
 }
 
-HfOverrides = Union[dict[str, Any], Callable[[PretrainedConfig],
-                                             PretrainedConfig]]
-
 
 class SupportsHash(Protocol):
 
@@ -365,7 +367,7 @@ def __init__(
         mm_processor_kwargs: Optional[dict[str, Any]] = None,
         disable_mm_preprocessor_cache: bool = False,
         override_neuron_config: Optional[dict[str, Any]] = None,
-        override_pooler_config: Optional["PoolerConfig"] = None,
+        override_pooler_config: Optional[PoolerConfig] = None,
         logits_processor_pattern: Optional[str] = None,
         generation_config: str = "auto",
         enable_sleep_mode: bool = False,
@@ -548,7 +550,7 @@ def __init__(
 
     @property
     def registry(self):
-        return ModelRegistry
+        return me_models.ModelRegistry
 
     @property
     def architectures(self) -> list[str]:
@@ -581,7 +583,7 @@ def maybe_pull_model_tokenizer_for_s3(self, model: str,
 
     def _init_multimodal_config(
         self, limit_mm_per_prompt: Optional[dict[str, int]]
-    ) -> Optional["MultiModalConfig"]:
+    ) -> Optional[MultiModalConfig]:
         if self.registry.is_multimodal_model(self.architectures):
             return MultiModalConfig(limit_per_prompt=limit_mm_per_prompt or {})
 
@@ -597,8 +599,8 @@ def _get_encoder_config(self):
 
     def _init_pooler_config(
         self,
-        override_pooler_config: Optional["PoolerConfig"],
-    ) -> Optional["PoolerConfig"]:
+        override_pooler_config: Optional[PoolerConfig],
+    ) -> Optional[PoolerConfig]:
 
         if self.runner_type == "pooling":
             user_config = override_pooler_config or PoolerConfig()
@@ -749,7 +751,8 @@ def _parse_quant_hf_config(self):
         return quant_cfg
 
     def _verify_quantization(self) -> None:
-        supported_quantization = QUANTIZATION_METHODS
+        supported_quantization = me_quant.QUANTIZATION_METHODS
+
         optimized_quantization_methods = [
             "fp8", "marlin", "modelopt", "gptq_marlin_24", "gptq_marlin",
             "awq_marlin", "fbgemm_fp8", "compressed_tensors",
@@ -766,8 +769,8 @@ def _verify_quantization(self) -> None:
             quant_method = quant_cfg.get("quant_method", "").lower()
 
             # Detect which checkpoint is it
-            for name in QUANTIZATION_METHODS:
-                method = get_quantization_config(name)
+            for name in me_quant.QUANTIZATION_METHODS:
+                method = me_quant.get_quantization_config(name)
                 quantization_override = method.override_quantization_method(
                     quant_cfg, self.quantization)
                 if quantization_override:
@@ -799,6 +802,8 @@ def _verify_quantization(self) -> None:
                     "non-quantized models.", self.quantization)
 
     def _verify_cuda_graph(self) -> None:
+        from vllm.platforms import current_platform
+
         if self.max_seq_len_to_capture is None:
             self.max_seq_len_to_capture = self.max_model_len
         self.max_seq_len_to_capture = min(self.max_seq_len_to_capture,
@@ -885,7 +890,7 @@ def verify_async_output_proc(self, parallel_config, speculative_config,
 
     def verify_with_parallel_config(
         self,
-        parallel_config: "ParallelConfig",
+        parallel_config: ParallelConfig,
     ) -> None:
 
         if parallel_config.distributed_executor_backend == "external_launcher":
@@ -1038,7 +1043,7 @@ def get_total_num_kv_heads(self) -> int:
         # equal to the number of attention heads.
         return self.hf_text_config.num_attention_heads
 
-    def get_num_kv_heads(self, parallel_config: "ParallelConfig") -> int:
+    def get_num_kv_heads(self, parallel_config: ParallelConfig) -> int:
         """Returns the number of KV heads per GPU."""
         if self.use_mla:
             # When using MLA during decode it becomes MQA
@@ -1052,13 +1057,12 @@ def get_num_kv_heads(self, parallel_config: "ParallelConfig") -> int:
         return max(1,
                    total_num_kv_heads // parallel_config.tensor_parallel_size)
 
-    def get_num_attention_heads(self,
-                                parallel_config: "ParallelConfig") -> int:
+    def get_num_attention_heads(self, parallel_config: ParallelConfig) -> int:
         num_heads = getattr(self.hf_text_config, "num_attention_heads", 0)
         return num_heads // parallel_config.tensor_parallel_size
 
     def get_layers_start_end_indices(
-            self, parallel_config: "ParallelConfig") -> tuple[int, int]:
+            self, parallel_config: ParallelConfig) -> tuple[int, int]:
         from vllm.distributed.utils import get_pp_indices
         if self.hf_text_config.model_type == "deepseek_mtp":
             total_num_hidden_layers = getattr(self.hf_text_config,
@@ -1073,13 +1077,13 @@ def get_layers_start_end_indices(
         start, end = get_pp_indices(total_num_hidden_layers, pp_rank, pp_size)
         return start, end
 
-    def get_num_layers(self, parallel_config: "ParallelConfig") -> int:
+    def get_num_layers(self, parallel_config: ParallelConfig) -> int:
         start, end = self.get_layers_start_end_indices(parallel_config)
         return end - start
 
     def get_num_layers_by_block_type(
         self,
-        parallel_config: "ParallelConfig",
+        parallel_config: ParallelConfig,
         block_type: LayerBlockType = LayerBlockType.attention,
     ) -> int:
         # This function relies on 'layers_block_type' in hf_config,
@@ -1132,7 +1136,7 @@ def get_num_layers_by_block_type(
 
             return sum(t == 1 for t in attn_type_list[start:end])
 
-    def get_multimodal_config(self) -> "MultiModalConfig":
+    def get_multimodal_config(self) -> MultiModalConfig:
         """
         Get the multimodal configuration of the model.
 
@@ -1241,7 +1245,7 @@ def runner_type(self) -> RunnerType:
     @property
     def is_v1_compatible(self) -> bool:
         architectures = getattr(self.hf_config, "architectures", [])
-        return ModelRegistry.is_v1_compatible(architectures)
+        return me_models.ModelRegistry.is_v1_compatible(architectures)
 
     @property
     def is_matryoshka(self) -> bool:
@@ -1392,7 +1396,7 @@ def _verify_prefix_caching(self) -> None:
 
     def verify_with_parallel_config(
         self,
-        parallel_config: "ParallelConfig",
+        parallel_config: ParallelConfig,
     ) -> None:
         total_cpu_memory = get_cpu_memory()
         # FIXME(woosuk): Here, it is assumed that the GPUs in a tensor parallel
@@ -1460,7 +1464,7 @@ class LoadConfig:
     """Configuration for loading the model weights."""
 
     load_format: Union[str, LoadFormat,
-                       "BaseModelLoader"] = LoadFormat.AUTO.value
+                       BaseModelLoader] = LoadFormat.AUTO.value
     """The format of the model weights to load:\n
     - "auto" will try to load the weights in the safetensors format and fall
     back to the pytorch bin format if safetensors format is not available.\n
@@ -1582,11 +1586,11 @@ def data_parallel_rank_local(self, value: int) -> None:
     ray_workers_use_nsight: bool = False
     """Whether to profile Ray workers with nsight, see https://docs.ray.io/en/latest/ray-observability/user-guides/profiling.html#profiling-nsight-profiler."""
 
-    placement_group: Optional["PlacementGroup"] = None
+    placement_group: Optional[PlacementGroup] = None
     """ray distributed model workers placement group."""
 
     distributed_executor_backend: Optional[Union[DistributedExecutorBackend,
-                                                 type["ExecutorBase"]]] = None
+                                                 type[ExecutorBase]]] = None
     """Backend to use for distributed model
     workers, either "ray" or "mp" (multiprocessing). If the product
     of pipeline_parallel_size and tensor_parallel_size is less than
@@ -1629,7 +1633,7 @@ def get_next_dp_init_port(self) -> int:
         self.data_parallel_master_port += 1
         return answer
 
-    def stateless_init_dp_group(self) -> "ProcessGroup":
+    def stateless_init_dp_group(self) -> ProcessGroup:
         from vllm.distributed.utils import (
             stateless_init_torch_distributed_process_group)
 
@@ -1644,7 +1648,7 @@ def stateless_init_dp_group(self) -> "ProcessGroup":
         return dp_group
 
     @staticmethod
-    def has_unfinished_dp(dp_group: "ProcessGroup",
+    def has_unfinished_dp(dp_group: ProcessGroup,
                           has_unfinished: bool) -> bool:
         tensor = torch.tensor([has_unfinished],
                               dtype=torch.int32,
@@ -2227,7 +2231,7 @@ def compute_hash(self) -> str:
         return hash_str
 
     @classmethod
-    def from_dict(cls, dict_value: dict) -> "SpeculativeConfig":
+    def from_dict(cls, dict_value: dict) -> SpeculativeConfig:
         """Parse the CLI value for the speculative config."""
         return cls(**dict_value)
 
@@ -2819,7 +2823,7 @@ def compute_hash(self) -> str:
         return hash_str
 
     @staticmethod
-    def from_json(json_str: str) -> "PoolerConfig":
+    def from_json(json_str: str) -> PoolerConfig:
         return PoolerConfig(**json.loads(json_str))
 
 
@@ -3176,6 +3180,7 @@ def compute_hash(self) -> str:
         return hash_str
 
     def __post_init__(self):
+        from vllm.tracing import is_otel_available, otel_import_error_traceback
         if not is_otel_available() and self.otlp_traces_endpoint is not None:
             raise ValueError(
                 "OpenTelemetry is not available. Unable to configure "
@@ -3239,7 +3244,7 @@ def compute_hash(self) -> str:
         return hash_str
 
     @classmethod
-    def from_cli(cls, cli_value: str) -> "KVTransferConfig":
+    def from_cli(cls, cli_value: str) -> KVTransferConfig:
         """Parse the CLI value for the kv cache transfer config."""
         return KVTransferConfig.model_validate_json(cli_value)
 
@@ -3476,7 +3481,7 @@ def __repr__(self) -> str:
     __str__ = __repr__
 
     @classmethod
-    def from_cli(cls, cli_value: str) -> "CompilationConfig":
+    def from_cli(cls, cli_value: str) -> CompilationConfig:
         """Parse the CLI value for the compilation config."""
         if cli_value in ["0", "1", "2", "3"]:
             return cls(level=int(cli_value))
@@ -3528,7 +3533,7 @@ def model_post_init(self, __context: Any) -> None:
         self.static_forward_context = {}
         self.compilation_time = 0.0
 
-    def init_backend(self, vllm_config: "VllmConfig") -> Union[str, Callable]:
+    def init_backend(self, vllm_config: VllmConfig) -> Union[str, Callable]:
         if self.level == CompilationLevel.NO_COMPILATION:
             raise ValueError("No compilation level is set.")
 
@@ -3744,9 +3749,7 @@ def _get_quantization_config(
         """Get the quantization config."""
         from vllm.platforms import current_platform
         if model_config.quantization is not None:
-            from vllm.model_executor.model_loader.weight_utils import (
-                get_quant_config)
-            quant_config = get_quant_config(model_config, load_config)
+            quant_config = me_quant.get_quant_config(model_config, load_config)
             capability_tuple = current_platform.get_device_capability()
 
             if capability_tuple is not None:
@@ -3770,7 +3773,7 @@ def with_hf_config(
         self,
         hf_config: PretrainedConfig,
         architectures: Optional[list[str]] = None,
-    ) -> "VllmConfig":
+    ) -> VllmConfig:
         if architectures is not None:
             hf_config = copy.deepcopy(hf_config)
             hf_config.architectures = architectures