[Model Runner V2][Minor] Simplify PP logic (#38031)

Signed-off-by: Nick Hill <nickhill123@gmail.com>

vllm/sequence.py

@@ -62,3 +62,12 @@ class IntermediateTensors:
 
     def __repr__(self) -> str:
         return f"IntermediateTensors(tensors={self.tensors})"
+
+    @staticmethod
+    def empty_like(
+        intermediate_tensors: "IntermediateTensors",
+    ) -> "IntermediateTensors":
+        tensors = {
+            k: torch.empty_like(v) for k, v in intermediate_tensors.tensors.items()
+        }
+        return IntermediateTensors(tensors)

vllm/v1/worker/gpu/cudagraph_utils.py

@@ -94,13 +94,8 @@ class CudaGraphManager:
         self.decode_query_len = decode_query_len
 
         self.dp_size = vllm_config.parallel_config.data_parallel_size
-        self.pp_size = vllm_config.parallel_config.pipeline_parallel_size
-        if self.pp_size > 1:
         self.is_first_pp_rank = get_pp_group().is_first_rank
         self.is_last_pp_rank = get_pp_group().is_last_rank
-        else:
-            self.is_first_pp_rank = True
-            self.is_last_pp_rank = True
 
         self.graphs: dict[BatchExecutionDescriptor, torch.cuda.CUDAGraph] = {}
         self.pool = current_platform.get_global_graph_pool() if cudagraph_mode else None
@@ -371,14 +366,11 @@ class ModelCudaGraphManager(CudaGraphManager):
                         self.aux_hidden_states[i][:num_tokens] = aux
                 else:
                     # Non-last PP rank.
+                    assert isinstance(model_output, IntermediateTensors)
                     intermediate_tensors = model_output
-                    assert isinstance(intermediate_tensors, IntermediateTensors)
                     if self.intermediate_tensors is None:
-                        self.intermediate_tensors = IntermediateTensors(
-                            {
-                                k: torch.empty_like(v)
-                                for k, v in intermediate_tensors.tensors.items()
-                            }
+                        self.intermediate_tensors = IntermediateTensors.empty_like(
+                            intermediate_tensors
                         )
                     for k, v in intermediate_tensors.tensors.items():
                         self.intermediate_tensors[k][:num_tokens] = v

vllm/v1/worker/gpu/model_runner.py

@@ -132,14 +132,10 @@ class GPUModelRunner(LoRAModelRunnerMixin):
         self.output_copy_event = torch.cuda.Event()
 
         # Pipeline parallelism.
-        self.pp_size = self.parallel_config.pipeline_parallel_size
-        self.use_pp = self.pp_size > 1
-        if self.use_pp:
+        self.use_pp = self.parallel_config.pipeline_parallel_size > 1
         self.is_first_pp_rank = get_pp_group().is_first_rank
         self.is_last_pp_rank = get_pp_group().is_last_rank
-        else:
-            self.is_first_pp_rank = True
-            self.is_last_pp_rank = True
+
         # Persistent buffer for intermediate tensors (non-first PP ranks).
         self.intermediate_tensors: IntermediateTensors | None = None
 
@@ -179,7 +175,7 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             if self.speculative_config.method == "eagle3":
                 # EAGLE3 may require auxiliary hidden states from target model outputs.
                 self.use_aux_hidden_state_outputs = True
-                if self.pp_size > 1:
+                if self.use_pp:
                     raise ValueError("EAGLE3 with pipeline parallel is not supported.")
 
         # Draft tokens propagation - for spec-dec + struct outputs.
@@ -270,8 +266,7 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             logger.info("Loading model from scratch...")
 
             self.model = model_loader.load_model(
-                vllm_config=self.vllm_config,
-                model_config=self.vllm_config.model_config,
+                vllm_config=self.vllm_config, model_config=self.vllm_config.model_config
             )
             if self.lora_config:
                 self.model = self.load_lora_model(
@@ -1026,14 +1021,13 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             assert intermediate_tensors is not None
             assert self.intermediate_tensors is not None
             n = input_batch.num_tokens_after_padding
-            intermediate_tensors = IntermediateTensors(
+            model_inputs["intermediate_tensors"] = IntermediateTensors(
                 {
                     k: v[:n].copy_(intermediate_tensors.tensors[k][:n])
                     for k, v in self.intermediate_tensors.tensors.items()
-                },
-                intermediate_tensors.kv_connector_output,
+                }
             )
-            model_inputs["intermediate_tensors"] = intermediate_tensors
+            del intermediate_tensors
 
         # Run model.
         if batch_desc.cg_mode == CUDAGraphMode.FULL: