Allowed modules are stuck into dynamo's fx graph as call_module
nodes, without dynamo doing any tracing of the module. This means
during AOT trace time, hooks will fire during tracing when the
call_module is executed, but the hooks themselves will disappear
after that and not be present in the compiled program.
(worse, if they performed any tensor operations, those would get
traced so you could end up with part of the hook's functionality).
To circumvent this, there are two options for 'allowed modules' with hooks.
1) don't treat them as 'allowed' - trace into them
2) graph-break, so the module is no longer part of the dynamo trace at all
(1) will fail for users that opted into allowed modules becuase they know
their module has problems being traced by dynamo.
(2) causes graph breaks on common modules such as nn.Linear, just because they
are marked as 'allowed'.
It would help matters if we could differentiate between types of allowed modules
(A) allowed to avoid overheads - used for common ops like nn.Linear
(B) allowed to avoid dynamo graphbreaks caused by unsupported code
Ideally, we'd use method (1) for group (A) and (2) for (B).
For now, graph-break on all cases of allowed modules.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97184
Approved by: https://github.com/jansel
This PR makes basic nnmodule forward hooks work by default, without any overhead. But it leaves silent correctness issues if users modify/remove their hooks later, thus also emits a warning.
- the usual case is to not use hooks, so avoid guard overhead here
- registering any hook before compile will trigger a warning about hook support
- registering a hook later (or removing one) requires user knowledge and opting in,
currently this isn't warnable (but maybe we can observe compiled nnmodules to make it
warnable).
Why skip hook guards by default instead of not tracing __call__/hooks by default?
- avoid having a mode flag that alters dynamo tracing behavior (harder to test both codepaths
in CI with full coverage)
- the most basic hook usecase (registering a hook before compile, and never removing it)
will work by default with this PR, while it would require enablement and incur overhead
in the 'not tracing __call__' proposal.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98371
Approved by: https://github.com/jansel
Chatted with @stas00 on slack and here are some great improvements he suggested to the compile docs
- [x] Rename `dynamo` folder to `compile`
- [x] Link `compile` docstring on `torch.html` to main index page for compile
- [x] Create a new index page that describes why people should care
- [x] easy perf, memory reduction, 1 line
- [x] Short benchmark table
- [x] How to guide
- [x] TOC that links to the more technical pages folks have written, make the existing docs we have a Technical overview
- [x] Highlight the new APIs for `torch._inductor.list_options()` and `torch._inductor.list_mode_options()` - clarify these are inductor specific and add more prose around which ones are most interesting
He also highlighted an interesting way to think about who is reading this doc we have
- [x] End users, that just want things to run fast
- [x] Library maintainers wrapping torch.compile which would care for example about understanding when in their code they should compile a model, which backends are supported
- [x] Debuggers who needs are somewhat addressed by the troubleshooting guide and faq but those could be dramatically reworked to say what we expect to break
And in a seperate PR I'll work on the below with @SherlockNoMad
- [ ] Authors of new backends that care about how to plug into dynamo or inductor layer so need to explain some more internals like
- [ ] IR
- [ ] Where to plugin, dynamo? inductor? triton?
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96706
Approved by: https://github.com/svekars
