FIX #7592 keeping chunked prefill performance the untouched

vllm/core/scheduler.py

@@ -510,6 +510,16 @@ def _schedule_running(
         # NOTE(woosuk): Preemption happens only when there is no available slot
         # to keep all the sequence groups in the RUNNING state.
 
+        if enable_chunking:
+            # By default, vLLM scheduler prioritizes prefills.
+            # Once chunked prefill is enabled,
+            # the policy is changed to prioritize decode requests.
+            self.running = deque(
+                sorted(
+                    self.running,
+                    key=lambda seq_group: seq_group.metrics.arrival_time,
+                ))
+
         running_queue = self.running
 
         while running_queue: