It's not surprising that TF is the slowest in many cases. It has been widely, sometimes harshly, criticized in the past for that reason. On the other hand, despite its speed TF appears to be the only tool that doesn't have to sit out any of the tests due to incompatibilities or lack of features. Other tools like MXNet deserve a shoutout as well, and it would be interesting to see how a wider group compares. MXNet als…
Clearly room for optimizing the CPU versions of things. That may be Eigen. Intel now has a preview out of their DNN toolkit -- I wonder if we'll see the same speed convergence as we did with CuDNN.