[4/N] make quant config first-class citizen (#9978)

Signed-off-by: youkaichao <youkaichao@gmail.com>

vllm/config.py

@@ -23,9 +23,13 @@ if TYPE_CHECKING:
     from ray.util.placement_group import PlacementGroup
 
     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
     from vllm.transformers_utils.tokenizer_group.base_tokenizer_group import (
         BaseTokenizerGroup)
+else:
+    QuantizationConfig = None
 
 logger = init_logger(__name__)
 
@@ -1966,6 +1970,35 @@ class VllmConfig:
     decoding_config: Optional[DecodingConfig] = None
     observability_config: Optional[ObservabilityConfig] = None
     prompt_adapter_config: Optional[PromptAdapterConfig] = None
+    quant_config: Optional[QuantizationConfig] = None
+
+    @staticmethod
+    def _get_quantization_config(
+            model_config: ModelConfig,
+            load_config: LoadConfig) -> Optional[QuantizationConfig]:
+        """Get the quantization config."""
+        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)
+            capability_tuple = current_platform.get_device_capability()
+
+            if capability_tuple is not None:
+                capability = capability_tuple.to_int()
+                if capability < quant_config.get_min_capability():
+                    raise ValueError(
+                        f"The quantization method {model_config.quantization} "
+                        "is not supported for the current GPU. Minimum "
+                        f"capability: {quant_config.get_min_capability()}. "
+                        f"Current capability: {capability}.")
+            supported_dtypes = quant_config.get_supported_act_dtypes()
+            if model_config.dtype not in supported_dtypes:
+                raise ValueError(
+                    f"{model_config.dtype} is not supported for quantization "
+                    f"method {model_config.quantization}. Supported dtypes: "
+                    f"{supported_dtypes}")
+            return quant_config
+        return None
 
     def __post_init__(self):
         """Verify configs are valid & consistent with each other.
@@ -1983,3 +2016,8 @@ class VllmConfig:
         if self.prompt_adapter_config:
             self.prompt_adapter_config.verify_with_model_config(
                 self.model_config)
+
+        if self.quant_config is None and \
+            self.model_config is not None and self.load_config is not None:
+            self.quant_config = VllmConfig._get_quantization_config(
+                self.model_config, self.load_config)