[Core] Add torch profiler CPU traces for AsyncLLM. (#21794)

Signed-off-by: Chenheli Hua <huachenheli@outlook.com>

vllm/envs.py

@@ -667,8 +667,10 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_LORA_RESOLVER_CACHE_DIR":
     lambda: os.getenv("VLLM_LORA_RESOLVER_CACHE_DIR", None),
 
-    # Enables torch profiler if set. Path to the directory where torch profiler
-    # traces are saved. Note that it must be an absolute path.
+    # Enables torch profiler if set.
+    # Both AsyncLLM's CPU traces as well as workers'
+    # traces (CPU & GPU) will be saved under this directory.
+    # 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", "."))),

vllm/v1/engine/async_llm.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import asyncio
+import os
+import socket
 import time
 from collections.abc import AsyncGenerator, Iterable, Mapping
 from copy import copy
 from typing import Any, Optional, Union
 
 import numpy as np
+import torch
 
 import vllm.envs as envs
 from vllm.config import ModelConfig, VllmConfig
@@ -144,6 +147,26 @@ class AsyncLLM(EngineClient):
         except RuntimeError:
             pass
 
+        if envs.VLLM_TORCH_PROFILER_DIR:
+            logger.info(
+                "Torch profiler enabled. AsyncLLM CPU traces will be collected under %s",  # noqa: E501
+                envs.VLLM_TORCH_PROFILER_DIR)
+            worker_name = f"{socket.gethostname()}_{os.getpid()}.async_llm"
+            self.profiler = torch.profiler.profile(
+                activities=[
+                    torch.profiler.ProfilerActivity.CPU,
+                ],
+                with_stack=envs.VLLM_TORCH_PROFILER_WITH_STACK,
+                on_trace_ready=torch.profiler.tensorboard_trace_handler(
+                    envs.VLLM_TORCH_PROFILER_DIR,
+                    worker_name=worker_name,
+                    use_gzip=True))
+        else:
+            logger.info(
+                "Torch profiler disabled. AsyncLLM CPU traces will not be collected."  # noqa: E501
+            )
+            self.profiler = None
+
     @classmethod
     @deprecate_kwargs(
         "disable_log_requests",
@@ -562,10 +585,16 @@ class AsyncLLM(EngineClient):
             raise self.dead_error
 
     async def start_profile(self) -> None:
-        await self.engine_core.profile_async(True)
+        coros = [self.engine_core.profile_async(True)]
+        if self.profiler is not None:
+            coros.append(asyncio.to_thread(self.profiler.start))
+        await asyncio.gather(*coros)
 
     async def stop_profile(self) -> None:
-        await self.engine_core.profile_async(False)
+        coros = [self.engine_core.profile_async(False)]
+        if self.profiler is not None:
+            coros.append(asyncio.to_thread(self.profiler.stop))
+        await asyncio.gather(*coros)
 
     async def reset_mm_cache(self) -> None:
         self.processor.mm_registry.reset_processor_cache(self.model_config)