Add CPU LoRA training (#938)

(It's very slow)

modules/shared.py

@@ -90,7 +90,7 @@ parser.add_argument('--extensions', type=str, nargs="+", help='The list of exten
 parser.add_argument('--verbose', action='store_true', help='Print the prompts to the terminal.')
 
 # Accelerate/transformers
-parser.add_argument('--cpu', action='store_true', help='Use the CPU to generate text.')
+parser.add_argument('--cpu', action='store_true', help='Use the CPU to generate text. Warning: Training on CPU is extremely slow.')
 parser.add_argument('--auto-devices', action='store_true', help='Automatically split the model across the available GPU(s) and CPU.')
 parser.add_argument('--gpu-memory', type=str, nargs="+", help='Maxmimum GPU memory in GiB to be allocated per GPU. Example: --gpu-memory 10 for a single GPU, --gpu-memory 10 5 for two GPUs. You can also set values in MiB like --gpu-memory 3500MiB.')
 parser.add_argument('--cpu-memory', type=str, help='Maximum CPU memory in GiB to allocate for offloaded weights. Same as above.')

modules/training.py

@@ -238,7 +238,7 @@ def do_train(lora_name: str, micro_batch_size: int, batch_size: int, epochs: int
             warmup_steps=100,
             num_train_epochs=epochs,
             learning_rate=actual_lr,
-            fp16=True,
+            fp16=False if shared.args.cpu else True,
             logging_steps=20,
             evaluation_strategy="steps" if eval_data is not None else "no",
             save_strategy="steps",
@@ -248,7 +248,8 @@ def do_train(lora_name: str, micro_batch_size: int, batch_size: int, epochs: int
             save_total_limit=3,
             load_best_model_at_end=True if eval_data is not None else False,
             # TODO: Enable multi-device support
-            ddp_find_unused_parameters=None
+            ddp_find_unused_parameters=None,
+            no_cuda=shared.args.cpu
         ),
         data_collator=transformers.DataCollatorForLanguageModeling(shared.tokenizer, mlm=False),
         callbacks=list([Callbacks()])