As one would expect, @ptrblck 's advice is the best you’d get. 



 ptrblck:

This would mean that unless your actual workload is small you shouldn’t see a huge difference between using the Python vs. C++ interface, but tom can correct me here.


Indeed, typical speedups I have seen are 1-10% (more the former for convnets, more the latter for RNN-type models e.g. for the LLTM tutorial example when you just convert to C++ but not implement custom kernels). The other part of that rule of thumb is something I have seen materialize, too: If the Python overhead is relatively costly, likely so is torch::Tensor creation at the C++ level.
Best regards
Thomas