Not so fast?
""The comparison doesn't look quite so rosy next to the current-gen Tesla P40 GPU, which advertises 47 INT8 TOP/s at 250W TDP; compared to the P40, the TPU is about 1.9x faster and 6.5x more energy-efficient," Johnson wrote."
Which is still a pretty decent margin really. Given that Google has been actually using these things since 2015, while the P40 was only announced a few months ago, that's still a pretty favourable comparison. Compared to contemporary competition, the TPU is way ahead; compared to modern competition, the TPU is still way ahead, just not by quite so much.
