Very low. A lot of the performance on GPUs comes from Nvidia's optimizations in CuDNN -- it's mostly a matter of making sure TensorFlow feeds the right formats

Very low. A lot of the performance on GPUs comes from Nvidia's optimizations in CuDNN -- it's mostly a matter of making sure TensorFlow feeds the right formats/etc. to CuDNN for core NN ops. TF should run well on CPUs, GPUs, TPUs, and likely future embedded accelerators (via tensorflow lite, which already supports the Android Neural Networks API). (I'm part time on Brain, but, of course, this isn't some kind of Official Statement(tm)).