[DDP] Profile search_unused_parameters (#57376)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57376
Having this in profiler/trace outputs will be useful when
investigating performance overhead of find_unused_parameters for certain
workloads, to determine whether it is a bottleneck or not.
ghstack-source-id: 127942159
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D28126233
fbshipit-source-id: 93082ae5b84e64351d59447a29f97eaf9b0bbd64
