[Easy] Fix the function signature of torch.Event (#151221)

As the title stated.

The difference between declaration and implemention.
declaration:
d5a19e4525/torch/_C/__init__.pyi.in (L157-L162)

Implementation:
d5a19e4525/torch/csrc/Event.cpp (L30-L32)

**Question**: Which one should we choose?
- Change enable_timing to False to be consistent with torch.cuda.Event
- Change enable_timing to True to avoid BC-break
Pull Request resolved: https://github.com/pytorch/pytorch/pull/151221
Approved by: https://github.com/albanD
ghstack dependencies: #151226

test/test_accelerator.py

@@ -129,6 +129,17 @@ class TestAccelerator(TestCase):
         ):
             event1.elapsed_time(event2)
 
+        # check default value of enable_timing: False
+        event1 = torch.Event()
+        event2 = torch.Event()
+        event1.record()
+        event2.record()
+        with self.assertRaisesRegex(
+            ValueError,
+            "Both events must be created with argument 'enable_timing=True'",
+        ):
+            event1.elapsed_time(event2)
+
 
 if __name__ == "__main__":
     run_tests()

test/test_cuda.py

@@ -985,6 +985,17 @@ class TestCuda(TestCase):
         ):
             event1.elapsed_time(event2)
 
+        # check default value of enable_timing: False
+        event1 = torch.cuda.Event()
+        event2 = torch.cuda.Event()
+        event1.record()
+        event2.record()
+        with self.assertRaisesRegex(
+            ValueError,
+            "Both events must be created with argument 'enable_timing=True'",
+        ):
+            event1.elapsed_time(event2)
+
     def test_generic_stream_event(self):
         stream = torch.Stream("cuda")
         self.assertEqual(stream.device_index, torch.cuda.current_device())

torch/csrc/Event.cpp

@@ -28,7 +28,7 @@ static PyObject* THPEvent_pynew(
   unsigned char interprocess = 0;
 
   static torch::PythonArgParser parser({
-      "Event(Device device=None, *, bool enable_timing=True, bool blocking=False, bool interprocess=False)",
+      "Event(Device device=None, *, bool enable_timing=False, bool blocking=False, bool interprocess=False)",
   });
 
   torch::ParsedArgs<4> parsed_args;
@@ -39,7 +39,7 @@ static PyObject* THPEvent_pynew(
   if (!device.has_value()) {
     device = at::Device(at::getAccelerator(false).value_or(at::kCPU));
   }
-  enable_timing = r.toBoolWithDefault(1, true);
+  enable_timing = r.toBoolWithDefault(1, false);
   blocking = r.toBoolWithDefault(2, false);
   interprocess = r.toBoolWithDefault(3, false);