[Core] Optimize scheduler request removal for single completions (#21917)

Signed-off-by: chiliu <chiliu@paypal.com>
Signed-off-by: chiliu <cliu_whu@yeah.net>
Co-authored-by: chiliu <chiliu@paypal.com>

vllm/v1/core/sched/scheduler.py

@@ -25,7 +25,7 @@ from vllm.v1.core.sched.output import (CachedRequestData, NewRequestData,
                                        SchedulerOutput)
 from vllm.v1.core.sched.request_queue import (SchedulingPolicy,
                                               create_request_queue)
-from vllm.v1.core.sched.utils import check_stop
+from vllm.v1.core.sched.utils import check_stop, remove_all
 from vllm.v1.engine import (EngineCoreEventType, EngineCoreOutput,
                             EngineCoreOutputs)
 from vllm.v1.kv_cache_interface import KVCacheConfig
@@ -872,9 +872,7 @@ class Scheduler(SchedulerInterface):
 
         # Remove the stopped requests from the running and waiting queues.
         if stopped_running_reqs:
-            self.running = [
-                req for req in self.running if req not in stopped_running_reqs
-            ]
+            self.running = remove_all(self.running, stopped_running_reqs)
         if stopped_preempted_reqs:
             # This is a rare case and unlikely to impact performance.
             self.waiting.remove_requests(stopped_preempted_reqs)
@@ -1000,7 +998,7 @@ class Scheduler(SchedulerInterface):
         else:
             request_ids = set(request_ids)
 
-        running_requests_to_remove = []
+        running_requests_to_remove = set()
         waiting_requests_to_remove = []
         valid_requests = []
 
@@ -1013,13 +1011,13 @@ class Scheduler(SchedulerInterface):
 
             valid_requests.append(request)
             if request.status == RequestStatus.RUNNING:
-                running_requests_to_remove.append(request)
+                running_requests_to_remove.add(request)
             else:
                 waiting_requests_to_remove.append(request)
 
         # Remove all requests from queues at once for better efficiency
-        for request in running_requests_to_remove:
-            self.running.remove(request)
+        if running_requests_to_remove:
+            self.running = remove_all(self.running, running_requests_to_remove)
         if waiting_requests_to_remove:
             self.waiting.remove_requests(waiting_requests_to_remove)
 

vllm/v1/core/sched/utils.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import contextlib
 from typing import Optional
 
 import torch
@@ -7,6 +8,38 @@ import torch
 from vllm.v1.request import Request, RequestStatus
 
 
+def remove_all(lst: list, items_to_remove: set) -> list:
+    """Remove all items from a list that are in the items_to_remove set.
+    
+    This method optimizes for the common case of removing a single item,
+    falling back to list comprehension for multiple items.
+    
+    Args:
+        lst: The list to remove items from
+        items_to_remove: Set of items to remove
+    
+    Returns:
+        Either the modified original list (for single item removal) or
+        a new list (for multiple item removal). Callers should use the
+        returned value.
+    
+    Note:
+        For single item removal, this modifies the original list in-place
+        and returns it. For multiple items, it creates and returns a new list.
+    """
+    if not items_to_remove:
+        return lst
+
+    if len(items_to_remove) == 1:
+        # Fast path for single item removal (most common case)
+        item = next(iter(items_to_remove))
+        with contextlib.suppress(ValueError):
+            lst.remove(item)
+        return lst
+    # For multiple items, use list comprehension
+    return [item for item in lst if item not in items_to_remove]
+
+
 def check_stop(request: Request,
                max_model_len: int,
                pooler_output: Optional[torch.Tensor] = None) -> bool: