[WIP][Core] Enable async scheduling by default

Signed-off-by: Nick Hill <[email protected]>

Author: njhill

vllm/config/scheduler.py

@@ -135,11 +135,12 @@ class SchedulerConfig:
     like full attention and sliding window attention.
     """
 
-    async_scheduling: bool = False
-    """If set to True, perform async scheduling. This helps to avoid gaps in
-    GPU utilization, leading to better latency and throughput.
-    Async scheduling is currently not supported with some features such as
-    speculative decoding and pipeline parallelism.
+    async_scheduling: bool = Field(default=None)
+    """If set to False, disable async scheduling. Async scheduling helps to
+    avoid gaps in GPU utilization, leading to better latency and throughput.
+    It is currently not supported with some features such as
+    speculative decoding and pipeline parallelism, and will be automatically
+    disabled in those cases.
     """
 
     def get_scheduler_cls(self) -> type["SchedulerInterface"]:

vllm/config/vllm.py

@@ -386,7 +386,6 @@ def __post_init__(self):
                 )
         elif self.scheduler_config.async_scheduling is None:
             # Enable async scheduling unless there is an incompatible option.
-            # NOTE: we won't reach here until async scheduling is enabled by default.
             if (
                 self.parallel_config.pipeline_parallel_size > 1
                 or self.speculative_config is not None