[Core][Logging] Add last frame information for better debugging (#4278)

Author: youkaichao

vllm/logger.py

@@ -83,13 +83,27 @@ def _trace_calls(log_path, root_dir, frame, event, arg=None):
             return
         # Log every function call or return
         try:
+            last_frame = frame.f_back
+            if last_frame is not None:
+                last_filename = last_frame.f_code.co_filename
+                last_lineno = last_frame.f_lineno
+                last_func_name = last_frame.f_code.co_name
+            else:
+                # initial frame
+                last_filename = ""
+                last_lineno = 0
+                last_func_name = ""
             with open(log_path, 'a') as f:
                 if event == 'call':
                     f.write(f"{datetime.datetime.now()} Call to"
-                            f" {func_name} in {filename}:{lineno}\n")
+                            f" {func_name} in {filename}:{lineno}"
+                            f" from {last_func_name} in {last_filename}:"
+                            f"{last_lineno}\n")
                 else:
                     f.write(f"{datetime.datetime.now()} Return from"
-                            f" {func_name} in {filename}:{lineno}\n")
+                            f" {func_name} in {filename}:{lineno}"
+                            f" to {last_func_name} in {last_filename}:"
+                            f"{last_lineno}\n")
         except NameError:
             # modules are deleted during shutdown
             pass