Refactor: Move CUDA graph dispatch logic earlier

Moves the CUDA graph dispatch logic to execute before the attention metadata is calculated within the dummy run.

Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>

Author: yiz-liu

vllm/v1/worker/gpu_model_runner.py

@@ -3521,6 +3521,31 @@ def _dummy_run(
             dp_rank = self.parallel_config.data_parallel_rank
             num_tokens_after_padding = int(num_tokens_across_dp[dp_rank])
 
+        # filter out the valid batch descriptor
+        _cg_mode, batch_descriptor = (
+            self.cudagraph_dispatcher.dispatch(
+                BatchDescriptor(
+                    num_tokens=num_tokens_after_padding,
+                    uniform_decode=uniform_decode,
+                    has_lora=activate_lora and self.lora_config is not None,
+                )
+            )
+            if not is_profile
+            else (CUDAGraphMode.NONE, None)
+        )
+        if cudagraph_runtime_mode is not None:
+            # we allow forcing NONE when the dispatcher disagrees to support
+            # warm ups for cudagraph capture
+            assert (
+                cudagraph_runtime_mode == CUDAGraphMode.NONE
+                or cudagraph_runtime_mode == _cg_mode
+            ), (
+                f"Cudagraph runtime mode mismatch at dummy_run. "
+                f"Expected {_cg_mode}, but got {cudagraph_runtime_mode}."
+            )
+        else:
+            cudagraph_runtime_mode = _cg_mode
+
         attn_metadata: PerLayerAttnMetadata | None = None
 
         # If force_attention is True, we always capture attention. Otherwise,
@@ -3595,31 +3620,6 @@ def _dummy_run(
                     num_tokens_after_padding, None, False
                 )
 
-            # filter out the valid batch descriptor
-            _cg_mode, batch_descriptor = (
-                self.cudagraph_dispatcher.dispatch(
-                    BatchDescriptor(
-                        num_tokens=num_tokens_after_padding,
-                        uniform_decode=uniform_decode,
-                        has_lora=activate_lora and self.lora_config is not None,
-                    )
-                )
-                if not is_profile
-                else (CUDAGraphMode.NONE, None)
-            )
-            if cudagraph_runtime_mode is not None:
-                # we allow forcing NONE when the dispatcher disagrees to support
-                # warm ups for cudagraph capture
-                assert (
-                    cudagraph_runtime_mode == CUDAGraphMode.NONE
-                    or cudagraph_runtime_mode == _cg_mode
-                ), (
-                    f"Cudagraph runtime mode mismatch at dummy_run. "
-                    f"Expected {_cg_mode}, but got {cudagraph_runtime_mode}."
-                )
-            else:
-                cudagraph_runtime_mode = _cg_mode
-
             if ubatch_slices is not None:
                 # Adjust values to reflect a single ubatch.
                 # TODO(sage,lucas): this is cruft that should be addressed in