benchmark

6b13e204 - Fix PyTorch unet train, only use mixed precision in forward pass. (#873)

Fix PyTorch unet train, only use mixed precision in forward pass. (#873) Summary: We should only apply amp on the forward pass in training, not backward pass. Pull Request resolved: https://github.com/pytorch/benchmark/pull/873 Reviewed By: erichan1 Differential Revision: D35765808 Pulled By: xuzhao9 fbshipit-source-id: 795e308c2ddee391952973ba901b7531f1870541