Update real_accelerator.py (#6845)

### Comment out or delete `accelerate_name="cpu"` when `xpu` is not
detected.
When `xpu `is not detected it just pass at lines from 68 to 74 if
`DS_ACCELERATOR` is set. However, `cpu` is assigned to `accelerate_name`
if it cannot import `intel_extension_for_pytorch` or find` xpu`, namely,
at line from 125 to 133 when`DS_ACCELERATOR` is not set.

I found this problem yesterday and spent whole afternoon figuring it
out. I got `intel_extension_for_pytorch `installed with other package
which I do not use actually and have no idea about this. Then I found
that it `cpu` is assigned to accelerate_name directly if it cannot find
`xpu` and it affects `cuda` detection. In fact, `cpu` will be assigned
finally if `cuda` is even not detected at line from 170 to 177.

---------

Co-authored-by: Olatunji Ruwase <[email protected]>
Co-authored-by: Logan Adams <[email protected]>
Co-authored-by: Logan Adams <[email protected]>

accelerator/real_accelerator.py

@@ -125,10 +125,9 @@ def get_accelerator():
         if accelerator_name is None:
             try:
                 import intel_extension_for_pytorch as ipex
+
                 if ipex._C._has_xpu():
                     accelerator_name = "xpu"
-                else:
-                    accelerator_name = "cpu"
             except ImportError as e:
                 pass
         if accelerator_name is None:
@@ -162,7 +161,6 @@ def get_accelerator():
             except ImportError as e:
                 pass
         if accelerator_name is None:
-            # borrow this log from PR#5084
             try:
                 import torch
 
@@ -174,16 +172,16 @@ def get_accelerator():
                 # For reference: https://github.com/microsoft/DeepSpeed/pull/6810
                 if torch.cuda.device_count() > 0 and torch.cuda.is_available():  #ignore-cuda
                     accelerator_name = "cuda"
-                else:
-                    if accel_logger is not None:
-                        accel_logger.warn(
-                            "Setting accelerator to CPU. If you have GPU or other accelerator, we were unable to detect it."
-                        )
-                    accelerator_name = "cpu"
             except (RuntimeError, ImportError) as e:
                 # TODO need a more decent way to detect which accelerator to use, consider using nvidia-smi command for detection
-                accelerator_name = "cuda"
                 pass
+        if accelerator_name is None:
+            # borrow this log from PR#5084
+            if accel_logger is not None:
+                accel_logger.warn(
+                    "Setting accelerator to CPU. If you have GPU or other accelerator, we were unable to detect it.")
+            # cpu added as catch-all when accelerator detection fails
+            accelerator_name = "cpu"
 
         ds_set_method = "auto detect"