Model parallel (#538)

* model-parallel for single process

* fix device/device_map

* fix handling for device

src/axolotl/utils/bench.py

@@ -28,7 +28,7 @@ def gpu_memory_usage_smi(device=0):
 
 
 def log_gpu_memory_usage(log, msg, device):
-    if not torch.cuda.is_available():
+    if not torch.cuda.is_available() or device == "auto":
         return (0, 0, 0)
 
     usage, cache, misc = gpu_memory_usage_all(device)

src/axolotl/utils/config.py

@@ -25,7 +25,9 @@ def choose_device(cfg):
             return "cpu"
 
     cfg.device = get_device()
-    if cfg.device_map != "auto":
+    if cfg.world_size == 1:
+        cfg.device_map = "auto"
+    else:
         if cfg.device.startswith("cuda"):
             cfg.device_map = {"": cfg.local_rank}
         else: