Add lightweight reparametrization for `_stateless` calls (#68969)
Summary:
https://github.com/pytorch/pytorch/issues/61447 introduced a mechanism for performing functional calls in a model using the reparametrization API. However, the overhead introduced in a single call was too large.
I tried to address this by modifying the reparametrization code to support spare tensors, but the changes needed were too large due to type checking and several parts of the code expecting actual `nn.Module` objects so this option was not feasible.
resnet50 and call functional with a parameters dict covering the 0, 25, 50, and 100% of the model total parameters.
Used script:
https://gist.github.com/emcastillo/f344a58638bd71d130c71c45f86f0c3a
| % of parameters passed | CPU Time (us) | GPU Time (us) |
|------------------------|---------------|---------------|
| regular call | 5539 | 184909 |
| 0 | 5561 | 184843 |
| 25 | 11363 | 189236 |
| 50 | 18716 | 195378 |
| 75 | 22851 | 198641 |
| 100 | 27441 | 202281 |
This PR just swaps the `__getattr__` of the submodules to look into a dict holding only the parameters when called, greatly reducing the burden of having to instantiate custom modules and calling forward to just retrieve a tensor.
The execution times now are as follows:
| % of parameters passed | CPU Time (us) | GPU Time (us) |
|------------------------|---------------|---------------|
| regular call | 5939 | 187533 |
| 0 | 5899 | 187570 |
| 25 | 8541 | 188953 |
| 50 | 10045 | 189826 |
| 75 | 11049 | 190344 |
| 100 | 11911 | 190800 |
| functorch with 100% params | 14014 | 191727
Now we see that the CPU time overhead is greatly reduced and the GPU time barely increases due to the effective overlap.
cc albanD zou3519
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68969
Reviewed By: george-qi
Differential Revision: D33836360
Pulled By: albanD
fbshipit-source-id: 532561f64b18ca14c6ae2d77dcacb339397a589d
(cherry picked from commit fd4b6bdfbff4cb3d1da47b7fd73f1edfe43ba65c)
pytorch
fa38e93f - Add lightweight reparametrization for `_stateless` calls (#68969)
