attention issue fix for fp16 inference (#794)
Summary:
The default min value will be overflow when model is under fp16. So I set a min val of fp16 for it.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/794
Reviewed By: xuzhao9
Differential Revision: D35020048
Pulled By: frank-wei
fbshipit-source-id: d5b11ae944dd4edc4eb8541a4f1780fa44fe28ab
