[Bug] Fix torch dynamo warning Dynamo detected a call to a functools.lru_cache (#29038)

Signed-off-by: yewentao256 <zhyanwentao@126.com>

vllm/model_executor/layers/batch_invariant.py

@@ -2,7 +2,6 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import os
 from collections.abc import Callable
-from functools import cache
 from typing import Any
 
 import torch
@@ -785,16 +784,19 @@ def enable_batch_invariant_mode():
     torch.backends.cuda.preferred_blas_library(backend="cublaslt")
 
 
-@cache
-def vllm_is_batch_invariant():
-    env_key = "VLLM_BATCH_INVARIANT"
-    is_overridden = False
-    val = os.getenv(env_key, "0")
+def _read_vllm_batch_invariant() -> bool:
+    val = os.getenv("VLLM_BATCH_INVARIANT", "0")
     try:
-        is_overridden = int(val) != 0
+        return int(val) != 0
     except ValueError:
-        is_overridden = False
-    return is_overridden
+        return False
+
+
+VLLM_BATCH_INVARIANT: bool = _read_vllm_batch_invariant()
+
+
+def vllm_is_batch_invariant() -> bool:
+    return VLLM_BATCH_INVARIANT
 
 
 def override_envs_for_invariance():