!4041 add overflow check for alexnet

Merge pull request !4041 from anzhengqi/modify-alexnet-imagenet

official/cv/alexnet/config_imagenet.yaml

@@ -29,7 +29,7 @@ keep_checkpoint_max: 10
 air_name: 'alexnet.air'
 
 weight_decay: 0.0001
-loss_scale: 1024
+loss_scale: 1
 is_dynamic_loss_scale: 0
 
 # Model Description

official/cv/alexnet/train.py

@@ -110,7 +110,7 @@ def train_alexnet():
         if config.is_dynamic_loss_scale == 1:
             loss_scale_manager = DynamicLossScaleManager(init_loss_scale=65536, scale_factor=2, scale_window=2000)
         else:
-            loss_scale_manager = FixedLossScaleManager(config.loss_scale, drop_overflow_update=False)
+            loss_scale_manager = FixedLossScaleManager(config.loss_scale, drop_overflow_update=True)
 
     else:
         raise ValueError("Unsupported dataset.")