title: What is cuDNN implementation of rnn cells in Tensorflow
body: <p>To create <code>RNN</code> cells, there are classes like <code>GRUCell</code> and <code>LSTMCell</code> which can be used later to create <code>RNN</code> layers.<br>
  And also there are 2 other classes as <code>CudnnGRU</code> and <code>CudnnLSTM</code> which can be directly used to create <code>RNN</code> layers.</p>
  
  <p>In the documentation they say that the latter classes have <code>cuDNN</code> implementation. Why should I use or not use this <code>cuDNN</code> implemented classes over classical <code>RNN</code> implementations when I'm creating a <code>RNN</code> model..?</p>