diff --git a/src/viztracer/main.py b/src/viztracer/main.py
index ab6cf210..f2dcbe90 100644
--- a/src/viztracer/main.py
+++ b/src/viztracer/main.py
@@ -600,7 +600,7 @@ def wait_children_finish(self) -> None:
                             if pid_exists(pid):
                                 break
                         else:   # pragma: no cover
-                            color_print("WARNING", f"Can't parse {viztmp_file}, skip")
+                            color_print("WARNING", f"Unknown viztmp file {viztmp_file}")
                     else:
                         break
                     time.sleep(0.5)
diff --git a/src/viztracer/util.py b/src/viztracer/util.py
index a1b5e31d..875d65c7 100644
--- a/src/viztracer/util.py
+++ b/src/viztracer/util.py
@@ -118,8 +118,8 @@ def pid_exists(pid):
         # On Windows, 0 is an idle process buw we don't need to
         # check it here
         raise ValueError('invalid PID 0')
-    # Windows
     if sys.platform == "win32":
+        # Windows
         kernel32 = ctypes.windll.kernel32
 
         process = kernel32.OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION, 0, pid)
@@ -153,8 +153,8 @@ def pid_exists(pid):
                 # Usually it's impossible to run here in viztracer.
                 return True
         return False    # pragma: no cover
-    # UNIX
     else:
+        # UNIX
         try:
             os.kill(pid, 0)
         except OSError as err:
diff --git a/tests/test_regression.py b/tests/test_regression.py
index 43f292e1..82481fe8 100644
--- a/tests/test_regression.py
+++ b/tests/test_regression.py
@@ -398,7 +398,7 @@ def target():
     p.start()
     # The main process will join the child in multiprocessing.process._children.
     # This is a hack to make sure the main process won't join the child process,
-    # so we can test the wait_children_finish function
+    # so we can test the VizUI.wait_children_finish function
     multiprocessing.process._children = set()
     time.sleep(1)
 """
@@ -418,7 +418,7 @@ def target():
     p.start()
     # The main process will join the child in multiprocessing.process._children.
     # This is a hack to make sure the main process won't join the child process,
-    # so we can test the wait_children_finish function
+    # so we can test the VizUI.wait_children_finish function
     multiprocessing.process._children = set()
     time.sleep(1)
 """