add num_runs flag to the benchmark (#22892)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22892
Think of num_runs as manually run the binary <num_runs> times. Each run runs the operator for many iterations.
Reviewed By: hl475
Differential Revision: D16271597
fbshipit-source-id: b6f509ee0332c70f85bec0d447b84940c5c0cecd
