  Neural Architecture Search (NAS) refers to automatically design the
architecture. We propose an hourglass-inspired approach (HourNAS) for this
problem that is motivated by the fact that the effects of the architecture
often proceed from the vital few blocks. Acting like the narrow neck of an
hourglass, vital blocks in the guaranteed path from the input to the output of
a deep neural network restrict the information flow and influence the network
accuracy. The other blocks occupy the major volume of the network and determine
the overall network complexity, corresponding to the bulbs of an hourglass. To
achieve an extremely fast NAS while preserving the high accuracy, we propose to
identify the vital blocks and make them the priority in the architecture
search. The search space of those non-vital blocks is further shrunk to only
cover the candidates that are affordable under the computational resource
constraints. Experimental results on the ImageNet show that only using 3 hours
(0.1 days) with one GPU, our HourNAS can search an architecture that achieves a
77.0% Top-1 accuracy, which outperforms the state-of-the-art methods.
