Make the split of batch outside GPUs (#51)

Tentative fix for issue #47

inception/inception/inception_train.py

@@ -221,27 +221,22 @@ def train(dataset):
     # Label 0 is reserved for an (unused) background class.
     num_classes = dataset.num_classes() + 1
     
+     # Split the batch of images and labels for towers.
+    images_splits = tf.split(0, FLAGS.num_gpus, images)
+    labels_splits = tf.split(0, FLAGS.num_gpus, labels)
+
     # Calculate the gradients for each model tower.
     tower_grads = []
     for i in xrange(FLAGS.num_gpus):
       with tf.device('/gpu:%d' % i):
         with tf.name_scope('%s_%d' % (inception.TOWER_NAME, i)) as scope:
-          # Split the batch of images and labels.
-          batch_start = split_batch_size * i
-          images_batch = tf.slice(images,
-                                  begin=[batch_start, 0, 0, 0],
-                                  size=[split_batch_size, -1, -1, -1])
-          labels_batch = tf.slice(labels,
-                                  begin=[batch_start],
-                                  size=[split_batch_size])
-
-
           # Force all Variables to reside on the CPU.
           with slim.arg_scope([slim.variables.variable], device='/cpu:0'):
             # Calculate the loss for one tower of the ImageNet model. This
             # function constructs the entire ImageNet model but shares the
             # variables across all towers.
-            loss = _tower_loss(images_batch, labels_batch, num_classes, scope)
+            loss = _tower_loss(images_splits[i], labels_splits[i], num_classes,
+                               scope)
 
           # Reuse variables for the next tower.
           tf.get_variable_scope().reuse_variables()