[aten] Pass std::function<> to thread_pool by value, instead of const ref. (#37681)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37681
By passing by value, we can std::move, and avoid unnecessarily copying
args that are part of any std::function/lambda state (e.g. in the jit
interpreter, there is a std::vector<> stack passed in the
InterpreterContinuation)
This makes the api also consistent with e.g. folly and best practices.
Added a minor at::launch() benchmark to test/cpp/, the difference is
mostly noticeable when copying the std::function<> internal args is
non-trivial.
Benchmarks pre/post (min over ~5 runs)
NoData: 5.81 us -> 5.63 us (-3.2%)
WithData(0): 6.67 us -> 5.88 us (-11.8%)
WithData(4): 6.98 us -> 6.51 us (-6.7%)
WithData(256): 9.44 us -> 7.89 (-16.5%)
ghstack-source-id: 103322321
Test Plan:
- perf: buck run mode/opt caffe2/test/cpp/api:parallel_benchmark pre/post
- correctness buck test mode/dev-nosan caffe2/test/...
Reviewed By: dzhulgakov
Differential Revision: D21355148
fbshipit-source-id: 3567e730845106f1991091e4a892d093e00571c3
