[misc] Add Torch profiler support for CPU-only devices (vllm-project#…

…7806)

vllm/worker/cpu_worker.py

@@ -179,6 +179,32 @@ def __init__(
         self.cache_engine: List[CPUCacheEngine]
         self.cpu_cache: List[List[torch.Tensor]]
 
+        # Torch profiler. Enabled and configured through env vars:
+        # VLLM_TORCH_PROFILER_DIR=/path/to/save/trace
+        if envs.VLLM_TORCH_PROFILER_DIR:
+            torch_profiler_trace_dir = envs.VLLM_TORCH_PROFILER_DIR
+            logger.info("Profiling enabled. Traces will be saved to: %s",
+                        torch_profiler_trace_dir)
+            self.profiler = torch.profiler.profile(
+                activities=[
+                    torch.profiler.ProfilerActivity.CPU,
+                ],
+                with_stack=True,
+                on_trace_ready=torch.profiler.tensorboard_trace_handler(
+                    torch_profiler_trace_dir, use_gzip=True))
+        else:
+            self.profiler = None
+
+    def start_profile(self):
+        if self.profiler is None:
+            raise RuntimeError("Profiler is not enabled.")
+        self.profiler.start()
+
+    def stop_profile(self):
+        if self.profiler is None:
+            raise RuntimeError("Profiler is not enabled.")
+        self.profiler.stop()
+
     def init_device(self) -> None:
         if self.local_omp_cpuid != "all":
             torch.ops._C_utils.init_cpu_threads_env(self.local_omp_cpuid)