[Core] Enable async scheduling for external_launcher mode (#27394)

Signed-off-by: 22quinn <33176974+22quinn@users.noreply.github.com>
Co-authored-by: Zhuohan Li <zhuohan123@gmail.com>

vllm/engine/arg_utils.py

@@ -1553,11 +1553,12 @@ class EngineArgs:
         )
 
         if self.async_scheduling and (
-            parallel_config.distributed_executor_backend not in ("mp", "uni")
+            parallel_config.distributed_executor_backend
+            not in ("mp", "uni", "external_launcher")
         ):
             raise ValueError(
-                "Currently, async scheduling only supports `mp` or `uni` "
-                "distributed executor backend, but you choose "
+                "Currently, async scheduling only supports `mp`, `uni` or "
+                "`external_launcher` distributed executor backend, but you choose "
                 f"`{parallel_config.distributed_executor_backend}`."
             )
 

vllm/v1/engine/llm_engine.py

@@ -306,9 +306,7 @@ class LLMEngine:
         self.engine_core.abort_requests(processed_outputs.reqs_to_abort)
 
         # 4) Record stats
-        if self.logger_manager is not None:
-            assert outputs.scheduler_stats is not None
-
+        if self.logger_manager is not None and outputs.scheduler_stats is not None:
             self.logger_manager.record(
                 scheduler_stats=outputs.scheduler_stats,
                 iteration_stats=iteration_stats,