What do the options in ConfigProto like allow_soft_placement and log_device_placement mean?

Question

We see this quite often in many of the TensorFlow tutorials:

sess = tf.Session(config=tf.ConfigProto(allow_soft_placem         


        

Answer 1

In addition to comments in tensorflow/core/protobuf/config.proto (allow_soft_placement, log_device_placement) it is also explained in TF's using GPUs tutorial.

To find out which devices your operations and tensors are assigned to, create the session with log_device_placement configuration option set to True.

Which is helpful for debugging. For each of the nodes of your graph, you will see the device it was assigned to.

---

If you would like TensorFlow to automatically choose an existing and supported device to run the operations in case the specified one doesn't exist, you can set allow_soft_placement to True in the configuration option when creating the session.

Which will help you if you accidentally manually specified the wrong device or a device which does not support a particular op. This is useful if you write a code which can be executed in environments you do not know. You still can provide useful defaults, but in the case of failure a graceful fallback.