[Core] LoRA: V1 Scheduler optimization (#15422)

Signed-off-by: Varun Sundar Rabindranath <varun@neuralmagic.com>
Co-authored-by: Varun Sundar Rabindranath <varun@neuralmagic.com>

vllm/v1/core/sched/scheduler.py

@@ -239,16 +239,16 @@ class Scheduler(SchedulerInterface):
                 encoder_budget = new_encoder_budget
 
         # Record the LoRAs in scheduled_running_reqs
-        requested_loras: set[int] = set()
+        scheduled_loras: set[int] = set()
         if self.lora_config:
-            requested_loras = set(
+            scheduled_loras = set(
                 req.lora_request.lora_int_id for req in scheduled_running_reqs
                 if req.lora_request and req.lora_request.lora_int_id > 0)
-            assert len(requested_loras) <= self.lora_config.max_loras
+            assert len(scheduled_loras) <= self.lora_config.max_loras
 
         # Use a temporary deque to collect requests that need to be skipped
         # and put back at the head of the waiting queue later
-        waiting_for_fsm: deque[Request] = deque()
+        skipped_waiting_requests: deque[Request] = deque()
 
         # Next, schedule the WAITING requests.
         if not preempted_reqs:
@@ -258,31 +258,30 @@ class Scheduler(SchedulerInterface):
 
                 request = self.waiting[0]
 
-                if request.status == RequestStatus.WAITING_FOR_FSM:
+                # Waiting request skipping logic
+                is_skipped = False
+                # Skip request if the structured output request is still waiting
+                # for FSM.
+                if (not is_skipped
+                        and request.status == RequestStatus.WAITING_FOR_FSM):
                     structured_output_req = request.structured_output_request
-                    if structured_output_req and structured_output_req.grammar:
+                    is_skipped = (not structured_output_req
+                                  or not structured_output_req.grammar)
+                    if not is_skipped:
                         request.status = RequestStatus.WAITING
-                    else:
-                        waiting_structured_output_req = self.waiting.popleft()
-                        waiting_for_fsm.appendleft(
-                            waiting_structured_output_req)
-                        continue
-
-                # Check that adding the request still respects the max_loras
-                # constraint.
-                if self.lora_config and request.lora_request:
+
+                # Skip request if max_loras can't be honored.
+                if (not is_skipped and self.lora_config
+                        and request.lora_request):
                     req_lora_id = request.lora_request.lora_int_id
-                    if len(requested_loras) == self.lora_config.max_loras and (
-                            req_lora_id not in requested_loras):
-                        # Cannot schedule.
-                        # TODO (varun): This means all the other requests in
-                        # the WAITING queue will be blocked by this request,
-                        # even if,
-                        # 1. these other requests do not use LoRA, or,
-                        # 2. these other requests use the already requested
-                        # LoRAs.
-                        # This is too conservative and could be optimized.
-                        break
+                    is_skipped = (len(scheduled_loras)
+                                  == self.lora_config.max_loras
+                                  and (req_lora_id not in scheduled_loras))
+
+                if is_skipped:
+                    skipped_waiting_requests.appendleft(request)
+                    self.waiting.popleft()
+                    continue
 
                 # Get already-cached tokens.
                 computed_blocks, num_computed_tokens = \
@@ -344,7 +343,7 @@ class Scheduler(SchedulerInterface):
                         f"Invalid request status: {request.status}")
 
                 if self.lora_config and request.lora_request:
-                    requested_loras.add(request.lora_request.lora_int_id)
+                    scheduled_loras.add(request.lora_request.lora_int_id)
                 req_to_new_block_ids[request.request_id] = [
                     b.block_id for b in computed_blocks + new_blocks
                 ]
@@ -363,8 +362,8 @@ class Scheduler(SchedulerInterface):
                     encoder_budget = new_encoder_budget
 
         # Put back any skipped requests at the head of the waiting queue
-        if waiting_for_fsm:
-            self.waiting.extendleft(waiting_for_fsm)
+        if skipped_waiting_requests:
+            self.waiting.extendleft(skipped_waiting_requests)
 
         # Check if the scheduling constraints are satisfied.
         total_num_scheduled_tokens = sum(num_scheduled_tokens.values())