revert acc changes (#9731)

* Revert "avoid per-batch blocking in metric (#9636)"

This reverts commit 3fe694e.

* Revert "proper flatten in acc (#9619)"

This reverts commit ed823b2.

* Revert "use nd for accuracy calculation (#9583)"

This reverts commit f5f1b91.

* keep doc change

python/mxnet/metric.py

@@ -28,7 +28,6 @@
 from .base import numeric_types, string_types
 from . import ndarray
 from . import registry
-from .context import cpu
 
 
 def check_label_shapes(labels, preds, shape=0):
@@ -389,22 +388,16 @@ def update(self, labels, preds):
         """
         check_label_shapes(labels, preds)
 
-        results = []
         for label, pred_label in zip(labels, preds):
             if pred_label.shape != label.shape:
                 pred_label = ndarray.argmax(pred_label, axis=self.axis)
-            pred_label = pred_label.astype('int32')
-            label = label.astype('int32')
+            pred_label = pred_label.asnumpy().astype('int32')
+            label = label.asnumpy().astype('int32')
 
             check_label_shapes(label, pred_label)
 
-            if pred_label.context != label.context:
-                pred_label = pred_label.as_in_context(label.context)
-
-            self.num_inst += pred_label.size
-            results.append((pred_label.reshape((-1,)) == label.reshape((-1,)))
-                           .sum().as_in_context(cpu()))
-        self.sum_metric += ndarray.add_n(*results).asscalar()
+            self.sum_metric += (pred_label.flat == label.flat).sum()
+            self.num_inst += len(pred_label.flat)
 
 
 @register