[Bugfix] Fix `vllm bench ...` on CPU-only head nodes (#25283)

Signed-off-by: Aydin Abiar <aydin@anyscale.com>
Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Aydin Abiar <aydin@anyscale.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>

vllm/entrypoints/cli/main.py

@@ -8,6 +8,11 @@ to avoid certain eager import breakage."""
 from __future__ import annotations
 
 import importlib.metadata
+import sys
+
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
 
 
 def main():
@@ -29,6 +34,22 @@ def main():
 
     cli_env_setup()
 
+    # For 'vllm bench *': use CPU instead of UnspecifiedPlatform by default
+    if len(sys.argv) > 1 and sys.argv[1] == "bench":
+        logger.debug(
+            "Bench command detected, must ensure current platform is not "
+            "UnspecifiedPlatform to avoid device type inference error"
+        )
+        from vllm import platforms
+
+        if platforms.current_platform.is_unspecified():
+            from vllm.platforms.cpu import CpuPlatform
+
+            platforms.current_platform = CpuPlatform()
+            logger.info(
+                "Unspecified platform detected, switching to CPU Platform instead."
+            )
+
     parser = FlexibleArgumentParser(
         description="vLLM CLI",
         epilog=VLLM_SUBCMD_PARSER_EPILOG.format(subcmd="[subcommand]"),

vllm/platforms/__init__.py

@@ -261,4 +261,14 @@ def __getattr__(name: str):
         raise AttributeError(f"No attribute named '{name}' exists in {__name__}.")
 
 
+def __setattr__(name: str, value):
+    if name == "current_platform":
+        global _current_platform
+        _current_platform = value
+    elif name in globals():
+        globals()[name] = value
+    else:
+        raise AttributeError(f"No attribute named '{name}' exists in {__name__}.")
+
+
 __all__ = ["Platform", "PlatformEnum", "current_platform", "CpuArchEnum", "_init_trace"]

vllm/platforms/interface.py

@@ -141,6 +141,9 @@ class Platform:
     def is_out_of_tree(self) -> bool:
         return self._enum == PlatformEnum.OOT
 
+    def is_unspecified(self) -> bool:
+        return self._enum == PlatformEnum.UNSPECIFIED
+
     def get_max_output_tokens(self, prompt_len: int) -> int:
         return sys.maxsize