[Model Runner V2] Limit cudagraph size to max decode batch size (#29221)

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

vllm/v1/worker/gpu/cudagraph_utils.py

@@ -27,9 +27,11 @@ class CudaGraphManager:
         device: torch.device,
     ):
         self.vllm_config = vllm_config
+        self.scheduler_config = vllm_config.scheduler_config
         self.device = device
 
         self.max_model_len = vllm_config.model_config.max_model_len
+        self.max_num_reqs = self.scheduler_config.max_num_seqs
         self.dp_size = vllm_config.parallel_config.data_parallel_size
         self.compilation_config = vllm_config.compilation_config
         assert self.compilation_config is not None
@@ -39,9 +41,11 @@ class CudaGraphManager:
         else:
             self.cudagraph_mode = self.compilation_config.cudagraph_mode
         if self.compilation_config.cudagraph_capture_sizes is not None:
-            self.cudagraph_sizes = sorted(
-                self.compilation_config.cudagraph_capture_sizes
-            )
+            cudagraph_sizes = sorted(self.compilation_config.cudagraph_capture_sizes)
+            # Limit the cudagraph sizes to the max decode batch size.
+            self.cudagraph_sizes = [
+                x for x in cudagraph_sizes if x <= self.max_num_reqs
+            ]
         else:
             self.cudagraph_sizes = []
         self.padded_sizes = self._init_padded_sizes()
@@ -54,9 +58,10 @@ class CudaGraphManager:
         if not self.cudagraph_mode.has_full_cudagraphs():
             # Full cuda graphs are not used.
             return {}
+        if not self.cudagraph_sizes:
+            return {}
 
         padded_sizes: dict[int, int] = {}
-        assert len(self.cudagraph_sizes) > 0
         for i in range(1, self.cudagraph_sizes[-1] + 1):
             for x in self.cudagraph_sizes:
                 if i <= x: