add always_use_cpu arg to bypass MPS

ldm/invoke/CLI.py

@@ -47,6 +47,7 @@ def main():
     # alert - setting globals here
     Globals.root = os.path.expanduser(args.root_dir or os.environ.get('INVOKEAI_ROOT') or os.path.abspath('.'))
     Globals.try_patchmatch = args.patchmatch
+    Globals.always_use_cpu = args.always_use_cpu
 
     print(f'>> InvokeAI runtime directory is "{Globals.root}"')
 

ldm/invoke/args.py

@@ -455,6 +455,12 @@ class Args(object):
             action='store_true',
             help='Force free gpu memory before final decoding',
         )
+        model_group.add_argument(
+            "--always_use_cpu",
+            dest="always_use_cpu",
+            action="store_true",
+            help="Force use of CPU even if GPU is available"
+        )
         model_group.add_argument(
             '--precision',
             dest='precision',

ldm/invoke/devices.py

@@ -1,9 +1,12 @@
 import torch
 from torch import autocast
 from contextlib import nullcontext
+from ldm.invoke.globals import Globals
 
 def choose_torch_device() -> str:
     '''Convenience routine for guessing which GPU device to run model on'''
+    if Globals.always_use_cpu:
+        return "cpu"
     if torch.cuda.is_available():
         return 'cuda'
     if hasattr(torch.backends, 'mps') and torch.backends.mps.is_available():

ldm/invoke/globals.py

@@ -8,6 +8,7 @@ the attributes:
   - root           - the root directory under which "models" and "outputs" can be found
   - initfile       - path to the initialization file
   - try_patchmatch - option to globally disable loading of 'patchmatch' module
+  - always_use_cpu - force use of CPU even if GPU is available
 '''
 
 import os
@@ -24,3 +25,6 @@ Globals.initfile = os.path.expanduser('~/.invokeai')
 # Awkward workaround to disable attempted loading of pypatchmatch
 # which is causing CI tests to error out.
 Globals.try_patchmatch = True
+
+# Use CPU even if GPU is available (main use case is for debugging MPS issues)
+Globals.always_use_cpu = False