[Perf] Cache vllm.env.__getattr__ result to avoid recomputation (#26146)

Signed-off-by: Jialin Ouyang <Jialin.Ouyang@gmail.com>

tests/test_envs.py

@@ -6,7 +6,54 @@ from unittest.mock import patch
 
 import pytest
 
-from vllm.envs import env_list_with_choices, env_with_choices
+import vllm.envs as envs
+from vllm.envs import (
+    enable_envs_cache,
+    env_list_with_choices,
+    env_with_choices,
+    environment_variables,
+)
+
+
+def test_getattr_without_cache(monkeypatch: pytest.MonkeyPatch):
+    assert envs.VLLM_HOST_IP == ""
+    assert envs.VLLM_PORT is None
+    monkeypatch.setenv("VLLM_HOST_IP", "1.1.1.1")
+    monkeypatch.setenv("VLLM_PORT", "1234")
+    assert envs.VLLM_HOST_IP == "1.1.1.1"
+    assert envs.VLLM_PORT == 1234
+    # __getattr__ is not decorated with functools.cache
+    assert not hasattr(envs.__getattr__, "cache_info")
+
+
+def test_getattr_with_cache(monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.setenv("VLLM_HOST_IP", "1.1.1.1")
+    monkeypatch.setenv("VLLM_PORT", "1234")
+    # __getattr__ is not decorated with functools.cache
+    assert not hasattr(envs.__getattr__, "cache_info")
+
+    # Enable envs cache and ignore ongoing environment changes
+    enable_envs_cache()
+
+    # __getattr__ is not decorated with functools.cache
+    assert hasattr(envs.__getattr__, "cache_info")
+    start_hits = envs.__getattr__.cache_info().hits
+
+    # 2 more hits due to VLLM_HOST_IP and VLLM_PORT accesses
+    assert envs.VLLM_HOST_IP == "1.1.1.1"
+    assert envs.VLLM_PORT == 1234
+    assert envs.__getattr__.cache_info().hits == start_hits + 2
+
+    # All environment variables are cached
+    for environment_variable in environment_variables:
+        envs.__getattr__(environment_variable)
+    assert envs.__getattr__.cache_info().hits == start_hits + 2 + len(
+        environment_variables
+    )
+
+    # Reset envs.__getattr__ back to none-cached version to
+    # avoid affecting other tests
+    envs.__getattr__ = envs.__getattr__.__wrapped__
 
 
 class TestEnvWithChoices: