[D] TPU lags behind GPU for Keras CNN training in Colab Pro

I have been comparing Colab's runtime. I found that for, for vanilla Keras CNN, TPU consistently lags behind A100, V100 or T4. Increasing batch-size didn't really improve it. Any specific configuration I should be investigating?

[Code](https://github.com/magurmach/TensorFlowLearning/blob/main/benchmarking/colab/CNN_on_fmnist_datase_Keras_Performance_evaluation.ipynb). [Blog post with details](https://medium.com/@008.shakib/comparing-keras-cnn-performance-in-colab-pro-runtimes-e7402499b61d).

a100 batch-size cnn colab found gpu keras machinelearning tpu training v100