[Core] Update dtype detection and defaults (#14858)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/v1/engine/test_llm_engine.py

@@ -50,7 +50,7 @@ def _get_test_sampling_params(
     """Generate random sampling params for a batch."""
 
     def get_mostly_n_gt1() -> int:
-        """Mostly n \in [2,20], ~1/3 n=1"""
+        r"""Mostly n \in [2,20], ~1/3 n=1"""
         x = random.randint(0, 28)
         if x < 10:
             return 1

vllm/config.py

@@ -347,7 +347,7 @@ class ModelConfig:
         self.encoder_config = self._get_encoder_config()
         self.hf_image_processor_config = get_hf_image_processor_config(
             self.model, revision)
-        self.dtype = _get_and_verify_dtype(self.hf_text_config, dtype)
+        self.dtype = _get_and_verify_dtype(self.hf_config, dtype)
         self.use_async_output_proc = use_async_output_proc
         self.mm_processor_kwargs = mm_processor_kwargs
         self.disable_mm_preprocessor_cache = disable_mm_preprocessor_cache
@@ -2526,6 +2526,14 @@ def _get_and_verify_dtype(
     # NOTE: getattr(config, "torch_dtype", torch.float32) is not correct
     # because config.torch_dtype can be None.
     config_dtype = getattr(config, "torch_dtype", None)
+
+    # Fallbacks for multi-modal models if the root config
+    # does not define torch_dtype
+    if config_dtype is None and hasattr(config, "text_config"):
+        config_dtype = getattr(config.text_config, "torch_dtype", None)
+    if config_dtype is None and hasattr(config, "vision_config"):
+        config_dtype = getattr(config.vision_config, "torch_dtype", None)
+
     if config_dtype is None:
         config_dtype = torch.float32
 
@@ -2533,16 +2541,8 @@ def _get_and_verify_dtype(
         dtype = dtype.lower()
         if dtype == "auto":
             if config_dtype == torch.float32:
-                if config.model_type in ("gemma2", "gemma3", "gemma3_text"):
-                    logger.info(
-                        "For Gemma 2 and 3, we downcast float32 to bfloat16 "
-                        "instead of float16 by default. Please specify `dtype` "
-                        "if you want to use float16.")
-                    torch_dtype = torch.bfloat16
-                else:
-                    # Following the common practice, we use float16 for float32
-                    # models.
-                    torch_dtype = torch.float16
+                # Following common practice, we use float16 for float32 models
+                torch_dtype = torch.float16
             else:
                 torch_dtype = config_dtype