[Feature] Add `VLLM_DISABLE_PAD_FOR_CUDAGRAPH` to Avoid Hang Issue (#23595)

Signed-off-by: yewentao256 <zhyanwentao@126.com>
Signed-off-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

vllm/envs.py

@@ -166,6 +166,7 @@ if TYPE_CHECKING:
     VLLM_USE_FLASHINFER_MOE_MXFP4_BF16: bool = False
     VLLM_ALLREDUCE_USE_SYMM_MEM: bool = False
     VLLM_TUNED_CONFIG_FOLDER: Optional[str] = None
+    VLLM_DISABLE_PAD_FOR_CUDAGRAPH: bool = False
 
 
 def get_default_cache_root():
@@ -1144,6 +1145,12 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_ENABLE_CUDAGRAPH_GC":
     lambda: bool(int(os.getenv("VLLM_ENABLE_CUDAGRAPH_GC", "0"))),
 
+    # Disable padding to CUDA graph capture batch sizes.
+    # TODO(wentao): https://github.com/vllm-project/vllm/issues/23378
+    # After the issue is fixed, we can remove this flag.
+    "VLLM_DISABLE_PAD_FOR_CUDAGRAPH":
+    lambda: bool(int(os.getenv("VLLM_DISABLE_PAD_FOR_CUDAGRAPH", "0"))),
+
     # Used to force set up loopback IP
     "VLLM_LOOPBACK_IP":
     lambda: os.getenv("VLLM_LOOPBACK_IP", ""),

vllm/v1/worker/gpu_model_runner.py

@@ -1491,6 +1491,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
 
         num_scheduled_tokens = scheduler_output.total_num_scheduled_tokens
         if (self.compilation_config.cudagraph_mode != CUDAGraphMode.NONE
+                and not envs.VLLM_DISABLE_PAD_FOR_CUDAGRAPH
                 and num_scheduled_tokens <= self.cudagraph_batch_sizes[-1]):
             # Use CUDA graphs.
             # Add padding to the batch size.