[Fix] Make autocast compatible with mps (#587)

* [Fix] Make autocast compatible with mps

* Enhance unit test

* fix unit test

* clean the code

* fix unit test

mmengine/runner/amp.py

@@ -121,9 +121,18 @@ def autocast(device_type: Optional[str] = None,
             assert dtype == torch.bfloat16, (
                 'In CPU autocast, only support `torch.bfloat16` dtype')
 
+        elif device_type == 'mlu':
+            pass
         else:
-            raise ValueError('User specified autocast device_type must be '
-                             F'cuda or cpu, but got {device_type}')
+            # Device like MPS does not support fp16 training or testing.
+            # If an inappropriate device is set and fp16 is enabled, an error
+            # will be thrown.
+            if enabled is False:
+                yield
+                return
+            else:
+                raise ValueError('User specified autocast device_type must be '
+                                 f'cuda or cpu, but got {device_type}')
 
         with torch.autocast(
                 device_type=device_type,

tests/test_runner/test_amp.py

@@ -4,6 +4,8 @@ import unittest
 import torch
 import torch.nn as nn
 
+import mmengine
+from mmengine.device import get_device
 from mmengine.runner import autocast
 from mmengine.utils import digit_version
 from mmengine.utils.dl_utils import TORCH_VERSION
@@ -56,3 +58,24 @@ class TestAmp(unittest.TestCase):
                     layer = nn.Conv2d(1, 1, 1).to(device)
                     res = layer(torch.randn(1, 1, 1, 1).to(device))
                     self.assertEqual(res.dtype, torch.float32)
+
+        # Test mps
+        if digit_version(TORCH_VERSION) >= digit_version('1.12.0'):
+            mmengine.runner.amp.get_device = lambda: 'mps'
+            with autocast(enabled=False):
+                layer = nn.Conv2d(1, 1, 1)
+                res = layer(torch.randn(1, 1, 1, 1))
+                self.assertEqual(res.dtype, torch.float32)
+
+            with self.assertRaisesRegex(ValueError,
+                                        'User specified autocast device_type'):
+                with autocast(enabled=True):
+                    pass
+        # Native pytorch does not support mlu, here we simply test autocast
+        # will call `torch.autocast`, which will be overridden by mlu version
+        # pytorch
+            mmengine.runner.amp.get_device = lambda: 'mlu'
+            with self.assertRaises(RuntimeError):
+                with autocast(enabled=False):
+                    pass
+            mmengine.runner.amp.get_device = get_device