Create good defaults in accelerate launch

src/accelerate/commands/launch.py

@@ -16,6 +16,7 @@
 
 import argparse
 import importlib
+import logging
 import os
 import subprocess
 import sys
@@ -24,6 +25,8 @@
 from pathlib import Path
 from typing import Dict, List
 
+import torch
+
 from accelerate.commands.config import default_config_file, load_config_from_file
 from accelerate.commands.config.config_args import SageMakerConfig
 from accelerate.utils import (
@@ -40,6 +43,9 @@
 from accelerate.utils.dataclasses import SageMakerDistributedType
 
 
+logger = logging.getLogger(__name__)
+
+
 def launch_command_parser(subparsers=None):
     if subparsers is not None:
         parser = subparsers.add_parser("launch")
@@ -684,15 +690,33 @@ def launch_command(args):
                     and getattr(args, name, None) is None
                 ):
                     setattr(args, name, attr)
-
         if not args.mixed_precision:
             if args.fp16:
                 args.mixed_precision = "fp16"
             else:
                 args.mixed_precision = defaults.mixed_precision
     else:
+        warned = False
         if args.num_processes is None:
+            logger.warn("`--num_processes` was not set, using a value of `1`.")
+            warned = True
             args.num_processes = 1
+        if args.num_machines is None:
+            warned = True
+            logger.warn("`--num_machines` was not set, using a value of `1`.")
+            args.num_machines = 1
+        if args.mixed_precision is None:
+            warned = True
+            logger.warn("`--mixed_precision` was not set, using a value of `'no'`.")
+            args.mixed_precision = "no"
+        if not hasattr(args, "use_cpu"):
+            args.use_cpu = args.cpu
+        if warned:
+            logger.warn("To avoid these warnings pass in values for each of the problematic parameters")
+
+    if args.multi_gpu and args.num_processes == 1:
+        logger.warn("`--multi_gpu` was passed but `num_processes` was not set. Automatically using all available GPUs")
+        args.num_processes = torch.cuda.device_count()
 
     # Use the proper launcher
     if args.use_deepspeed and not args.cpu: