[Serve.llm][Bugfix] Allow users to enable log_stats (ray-project#54719)

Signed-off-by: Seiji Eicher <[email protected]>
Signed-off-by: dshepelev15 <[email protected]>

Author: eicherseiji

python/ray/llm/_internal/serve/configs/server_models.py

@@ -18,6 +18,7 @@
     PositiveInt,
     PrivateAttr,
     field_validator,
+    model_validator,
 )
 
 import ray
@@ -311,6 +312,17 @@ def validate_deployment_config(cls, value: Dict[str, Any]) -> Dict[str, Any]:
 
         return value
 
+    @model_validator(mode="after")
+    def _check_log_stats_with_metrics(self):
+        # Require disable_log_stats is not set to True when log_engine_metrics is enabled.
+        if self.log_engine_metrics and self.engine_kwargs.get("disable_log_stats"):
+            raise ValueError(
+                "disable_log_stats cannot be set to True when log_engine_metrics is enabled. "
+                "Engine metrics require log stats to be enabled."
+            )
+
+        return self
+
     def multiplex_config(self) -> ServeMultiplexConfig:
         multiplex_config = None
         if self.lora_config:

python/ray/llm/_internal/serve/deployments/llm/vllm/vllm_models.py

@@ -136,15 +136,6 @@ def get_initialization_kwargs(self) -> dict:
         else:
             engine_kwargs["distributed_executor_backend"] = "ray"
 
-        if (
-            "disable_log_stats" in engine_kwargs
-            and not engine_kwargs["disable_log_stats"]
-        ):
-            logger.warning(
-                "disable_log_stats = False is not allowed in engine_kwargs when using Ray Serve LLM Configs. Setting it to True."
-            )
-        engine_kwargs["disable_log_stats"] = True
-
         return engine_kwargs
 
     def get_runtime_env_with_local_env_vars(self) -> dict:

python/ray/llm/tests/serve/cpu/configs/test_models.py

@@ -273,6 +273,18 @@ def test_experimental_configs(self):
                 experimental_configs={123: "value1"},
             )
 
+    def test_log_engine_metrics_disable_log_stats_validation(self):
+        """Test that log_engine_metrics=True prevents disable_log_stats=True."""
+        with pytest.raises(
+            pydantic.ValidationError,
+            match="disable_log_stats cannot be set to True when log_engine_metrics is enabled",
+        ):
+            LLMConfig(
+                model_loading_config=ModelLoadingConfig(model_id="test_model"),
+                log_engine_metrics=True,
+                engine_kwargs={"disable_log_stats": True},
+            )
+
 
 if __name__ == "__main__":
     sys.exit(pytest.main(["-v", __file__]))