Run fp16 resnext101 training in bench script (#17963)
Summary:
cc xw285cornell
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17963
Differential Revision: D14453445
Pulled By: bddppq
fbshipit-source-id: 7ca0e0c33ae89d4d4cf6ddba321daf4d6b2d5ed6
