[misc] Add Torch profiler support (#7451)

Co-authored-by: Cody Yu <hao.yu.cody@gmail.com>

vllm/envs.py

@@ -58,6 +58,7 @@ if TYPE_CHECKING:
     VLLM_TEST_FORCE_FP8_MARLIN: bool = False
     VLLM_ALLOW_ENGINE_USE_RAY: bool = False
     VLLM_PLUGINS: Optional[List[str]] = None
+    VLLM_TORCH_PROFILER_DIR: Optional[str] = None
 
 
 def get_default_cache_root():
@@ -384,6 +385,12 @@ environment_variables: Dict[str, Callable[[], Any]] = {
     "VLLM_PLUGINS":
     lambda: None if "VLLM_PLUGINS" not in os.environ else os.environ[
         "VLLM_PLUGINS"].split(","),
+
+    # Enables torch profiler if set. Path to the directory where torch profiler
+    # traces are saved. Note that it must be an absolute path.
+    "VLLM_TORCH_PROFILER_DIR":
+    lambda: (None if os.getenv("VLLM_TORCH_PROFILER_DIR", None) is None else os
+             .path.expanduser(os.getenv("VLLM_TORCH_PROFILER_DIR", "."))),
 }
 
 # end-env-vars-definition