[Model Runner V2] Refactor `update_states` (#32562)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

vllm/v1/worker/gpu/model_runner.py

@@ -425,7 +425,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
             self._dummy_run(self.max_num_tokens, skip_attn=False)
             torch.cuda.synchronize()
 
-    def update_states(self, scheduler_output: SchedulerOutput) -> None:
+    def finish_requests(self, scheduler_output: SchedulerOutput) -> None:
         if scheduler_output.preempted_req_ids is not None:
             for req_id in scheduler_output.preempted_req_ids:
                 self.req_states.remove_request(req_id)
@@ -436,11 +436,12 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
             if self.supports_mm_inputs:
                 self.encoder_runner.remove_request(req_id)
 
+    def free_states(self, scheduler_output: SchedulerOutput) -> None:
         if self.supports_mm_inputs:
             for mm_hash in scheduler_output.free_encoder_mm_hashes:
                 self.encoder_runner.free_encoder_cache(mm_hash)
 
-        # Add new requests.
+    def add_requests(self, scheduler_output: SchedulerOutput) -> None:
         for new_req_data in scheduler_output.scheduled_new_reqs:
             assert new_req_data.prompt_token_ids is not None
             assert new_req_data.prefill_token_ids is not None
@@ -476,6 +477,17 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 req_index, prompt_len, new_req_data.sampling_params
             )
 
+        if scheduler_output.scheduled_new_reqs:
+            self.req_states.apply_staged_writes()
+            self.sampler.apply_staged_writes(
+                self.req_states.prefill_token_ids.gpu,
+                self.req_states.prefill_len.np,
+                self.req_states.prompt_len,
+            )
+            if self.uses_mrope:
+                self.mrope_states.apply_staged_writes()
+
+    def update_requests(self, scheduler_output: SchedulerOutput) -> None:
         # Add new blocks for the existing requests.
         cached_reqs = scheduler_output.scheduled_cached_reqs
         for i, req_id in enumerate(cached_reqs.req_ids):
@@ -486,16 +498,6 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                     req_index, req_new_block_ids, overwrite=False
                 )
 
-        self.req_states.apply_staged_writes()
-        self.block_tables.apply_staged_writes()
-        self.sampler.apply_staged_writes(
-            self.req_states.prefill_token_ids.gpu,
-            self.req_states.prefill_len.np,
-            self.req_states.prompt_len,
-        )
-        if self.uses_mrope:
-            self.mrope_states.apply_staged_writes()
-
     def prepare_inputs(
         self,
         scheduler_output: SchedulerOutput,
@@ -951,15 +953,20 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         dummy_run: bool = False,
     ) -> ModelRunnerOutput | None:
         assert intermediate_tensors is None
-        if scheduler_output.total_num_scheduled_tokens == 0 and not dummy_run:
-            # No need to run the model.
-            self.update_states(scheduler_output)
-            return EMPTY_MODEL_RUNNER_OUTPUT
+        if not dummy_run:
+            # Update the request states.
+            self.finish_requests(scheduler_output)
+            self.free_states(scheduler_output)
+            self.add_requests(scheduler_output)
+            self.update_requests(scheduler_output)
+            self.block_tables.apply_staged_writes()
+            if scheduler_output.total_num_scheduled_tokens == 0:
+                # No need to run the model.
+                return EMPTY_MODEL_RUNNER_OUTPUT
 
         cudagraph_mode, num_tokens_after_padding, num_tokens_across_dp = (
             self.get_cudagraph_and_dp_padding(scheduler_output)
         )
-        self.update_states(scheduler_output)
         if num_tokens_after_padding == 0:
             # All DP ranks have zero tokens to run.
             return EMPTY_MODEL_RUNNER_OUTPUT