[Core] Batch multi modal input using pinned memory (#19169)

Signed-off-by: Lukas Geiger <lukas.geiger94@gmail.com>

vllm/multimodal/inputs.py

@@ -680,7 +680,8 @@ class MultiModalKwargs(UserDict[str, NestedTensors]):
         return self._items_by_modality.keys()
 
     @staticmethod
-    def _try_stack(nested_tensors: NestedTensors) -> NestedTensors:
+    def _try_stack(nested_tensors: NestedTensors,
+                   pin_memory: bool = False) -> NestedTensors:
         """
         Stack the inner dimensions that have the same shape in
         a nested list of tensors.
@@ -697,7 +698,9 @@ class MultiModalKwargs(UserDict[str, NestedTensors]):
         if isinstance(nested_tensors, (int, float)):
             return torch.tensor(nested_tensors)
 
-        stacked = [MultiModalKwargs._try_stack(t) for t in nested_tensors]
+        stacked = [
+            MultiModalKwargs._try_stack(t, pin_memory) for t in nested_tensors
+        ]
         if not is_list_of(stacked, torch.Tensor, check="all"):
             # Only tensors (not lists) can be stacked.
             return stacked
@@ -713,10 +716,16 @@ class MultiModalKwargs(UserDict[str, NestedTensors]):
             # The tensors have incompatible shapes and can't be stacked.
             return tensors_
 
-        return torch.stack(tensors_)
+        outputs = torch.empty(len(tensors_),
+                              *tensors_[0].shape,
+                              dtype=tensors_[0].dtype,
+                              device=tensors_[0].device,
+                              pin_memory=pin_memory)
+        return torch.stack(tensors_, out=outputs)
 
     @staticmethod
-    def batch(inputs_list: list["MultiModalKwargs"]) -> BatchedTensorInputs:
+    def batch(inputs_list: list["MultiModalKwargs"],
+              pin_memory: bool = False) -> BatchedTensorInputs:
         """
         Batch multiple inputs together into a dictionary.
 
@@ -738,7 +747,7 @@ class MultiModalKwargs(UserDict[str, NestedTensors]):
                 item_lists[k].append(v)
 
         return {
-            k: MultiModalKwargs._try_stack(item_list)
+            k: MultiModalKwargs._try_stack(item_list, pin_memory)
             for k, item_list in item_lists.items()
         }
 

vllm/v1/worker/gpu_model_runner.py

@@ -962,7 +962,8 @@ class GPUModelRunner(LoRAModelRunnerMixin):
 
         encoder_outputs = []
         for grouped_mm_inputs in grouped_mm_inputs_list:
-            batched_mm_inputs = MultiModalKwargs.batch(grouped_mm_inputs)
+            batched_mm_inputs = MultiModalKwargs.batch(
+                grouped_mm_inputs, pin_memory=self.pin_memory)
             batched_mm_inputs = MultiModalKwargs.as_kwargs(
                 batched_mm_inputs,
                 device=self.device,
@@ -1989,7 +1990,8 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             ).multi_modal_data
 
             batched_dummy_mm_inputs = MultiModalKwargs.batch(
-                [dummy_mm_kwargs] * max_num_mm_items)
+                [dummy_mm_kwargs] * max_num_mm_items,
+                pin_memory=self.pin_memory)
             batched_dummy_mm_inputs = MultiModalKwargs.as_kwargs(
                 batched_dummy_mm_inputs,
                 device=self.device,