Merge pull request #2044 from tfboyd/cifar_estimator

Enhanced comments and renamed ParamServerDeviceSetter

tutorials/image/cifar10_estimator/cifar10_main.py

@@ -98,16 +98,20 @@ tf.flags.DEFINE_boolean('log_device_placement', False,
                         'Whether to log device placement.')
 
 
-# TODO(jamesqin): Replace with fix in b/62239022
-class ParamServerDeviceSetter(object):
-  """Helper class to assign variables on the least loaded ps-device."""
+class GpuParamServerDeviceSetter(object):
+  """Used with tf.device() to place variables on the least loaded GPU.
 
-  def __init__(self, worker_device, ps_devices):
-    """Initializer for ParamServerDeviceSetter.
+    A common use for this class is to pass a list of GPU devices, e.g. ['gpu:0',
+    'gpu:1','gpu:2'], as ps_devices.  When each variable is placed, it will be
+    placed on the least loaded gpu. All other Ops, which will be the computation
+    Ops, will be placed on the worker_device.
+  """
 
+  def __init__(self, worker_device, ps_devices):
+    """Initializer for GpuParamServerDeviceSetter.
     Args:
-      worker_device: the device to use for computer ops.
-      ps_devices: a list of devices to use for Variable ops. Each variable is
+      worker_device: the device to use for computation Ops.
+      ps_devices: a list of devices to use for Variable Ops. Each variable is
       assigned to the least loaded device.
     """
     self.ps_devices = ps_devices
@@ -120,6 +124,7 @@ class ParamServerDeviceSetter(object):
     if op.type not in ['Variable', 'VariableV2', 'VarHandleOp']:
       return self.worker_device
       
+    # Gets the least loaded ps_device
     device_index, _ = min(enumerate(self.ps_sizes), key=operator.itemgetter(1))
     device_name = self.ps_devices[device_index]
     var_size = op.outputs[0].get_shape().num_elements()
@@ -127,15 +132,16 @@ class ParamServerDeviceSetter(object):
 
     return device_name
 
-
-def _create_device_setter(is_cpu_ps, worker):
+def _create_device_setter(is_cpu_ps, worker, num_gpus):
   """Create device setter object."""
   if is_cpu_ps:
+    # tf.train.replica_device_setter supports placing variables on the CPU, all
+    # on one GPU, or on ps_servers defined in a cluster_spec.
     return tf.train.replica_device_setter(
         worker_device=worker, ps_device='/cpu:0', ps_tasks=1)
   else:
-    gpus = ['/gpu:%d' % i for i in range(FLAGS.num_gpus)]
-    return ParamServerDeviceSetter(worker, gpus)
+    gpus = ['/gpu:%d' % i for i in range(num_gpus)]
+    return GpuParamServerDeviceSetter(worker, gpus)
 
 
 def _resnet_model_fn(features, labels, mode):
@@ -169,7 +175,7 @@ def _resnet_model_fn(features, labels, mode):
   if num_gpus != 0:
     for i in range(num_gpus):
       worker = '/gpu:%d' % i
-      device_setter = _create_device_setter(is_cpu_ps, worker)
+      device_setter = _create_device_setter(is_cpu_ps, worker, FLAGS.num_gpus)
       with tf.variable_scope('resnet', reuse=bool(i != 0)):
         with tf.name_scope('tower_%d' % i) as name_scope:
           with tf.device(device_setter):