[misc] skip p2p check by default (#21904)

vllm/envs.py

@@ -668,12 +668,14 @@ environment_variables: dict[str, Callable[[], Any]] = {
     (os.environ.get("VLLM_ALLOW_RUNTIME_LORA_UPDATING", "0").strip().lower() in
      ("1", "true")),
 
-    # By default, vLLM will check the peer-to-peer capability itself,
-    # in case of broken drivers. See https://github.com/vllm-project/vllm/blob/a9b15c606fea67a072416ea0ea115261a2756058/vllm/distributed/device_communicators/custom_all_reduce_utils.py#L101-L108 for details. # noqa
-    # If this env var is set to 1, vLLM will skip the peer-to-peer check,
-    # and trust the driver's peer-to-peer capability report.
+    # We assume drivers can report p2p status correctly.
+    # If the program hangs when using custom allreduce,
+    # potantially caused by a bug in the driver (535 series),
+    # if might be helpful to set VLLM_SKIP_P2P_CHECK=0
+    # so that vLLM can verify if p2p is actually working.
+    # See https://github.com/vllm-project/vllm/blob/a9b15c606fea67a072416ea0ea115261a2756058/vllm/distributed/device_communicators/custom_all_reduce_utils.py#L101-L108 for details. # noqa
     "VLLM_SKIP_P2P_CHECK":
-    lambda: os.getenv("VLLM_SKIP_P2P_CHECK", "0") == "1",
+    lambda: os.getenv("VLLM_SKIP_P2P_CHECK", "1") == "1",
 
     # List of quantization kernels that should be disabled, used for testing
     # and performance comparisons. Currently only affects MPLinearKernel