Summary:
When creating a new DDP instance for the same model when an old DDP instance existed, the autograd hooks from the old DDP instance might not be cleared. Also, relying on python gc to clear out old autograd hooks is fragile and may not work 100% of the time.
As a result, in this PR I'm adding a way to explicitly remove these hooks from DDP
Test Plan:
Unit test added
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96490
Approved by: https://github.com/zhaojuanmao, https://github.com/rohan-varma
Summary: Enable the functionality of delaying all reduce in DDP to specify the parameters whose all reduce will be hooked to a specific param. This prevents AllReduce blocking All2All in some recommendation models.
Test Plan: GitHub CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96673
Approved by: https://github.com/zhaojuanmao
Implements native mixed precision support for DDP in a similar fashion to how it is enabled for FSDP. The implementation works as follows:
1. In DDP init, we save `_mp_param` and `_fp_param` variables to manage mixed precision parameter usage. In particular, _mp_param will represent the parameter in the reduced precision, while _fp_param will represent the param in regular precision. During forward/backward, we swap back and forth as needed.
2. The root module gets a root pre-forward hook that kicks off copies to the reduced precision for all submodules. An event is recorded for each submodule to allow for waiting, as we run these asynchronously.
3. Each module gets a pre-forward hook that waits on its corresponding event. note that modules might be reused during training, in this case the wait is only done for the first module. After this wait, the module's parameters are in reduced precision.
4. In the pre-forward hook, we register a backward hook on the lower precision parameters in order to run reduced precision allreduce + parameter upcast. We can't rely on the Reducer's constructor setting up these hooks because the gradient is accumulated on the low precision param, so we need to register them ourselves.
5. In the backward pass, when the hook runs, we first run allreduce + divide in the reduced precision. Next, we upcast parameters and gradients back to fp32 asynchronously. We also queue a callback at the end of backward to wait on these upcasts so that the upcast is complete before optim.step() runs.
6. Parameters that don't require grad are also cast since they may be used in computation, they are upcast back in the final autograd callback.
7. DDP Ignored parameters are not touched.
Follow-ups:
1. Unify comm hooks and make it work with apply optimizer in backward
2. implement keep_low_precision_grads,
3. allow BN, LN, or custom units to run in reduced precision,
4. support for cast_forward_inputs
5. Unify certain APIs / helpers with FSDP where possible, such as for _cast_forward_inputs
6. Integrate this with replicate() API.
7. The order in which we kick off copies and wait for them is set by the iteration order of module.modules(), but this might not be how the modules are used in the actual training. In the worst case, the last module in module.modules() could be used first which would result in waiting for all copies unnecessarily. For static graphs, we should record the module execution order and copy / wait in this order.
8. Entirely unused modules probably don't need to be cast.
Differential Revision: [D42515803](https://our.internmc.facebook.com/intern/diff/D42515803/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92882
Approved by: https://github.com/zhaojuanmao
Applies the remaining flake8-comprehension fixes and checks. This changes replace all remaining unnecessary generator expressions with list/dict/set comprehensions which are more succinct, performant, and better supported by our torch.jit compiler. It also removes useless generators such as 'set(a for a in b)`, resolving it into just the set call.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94676
Approved by: https://github.com/ezyang
Applies some more harmless pyupgrades. This one gets rid of deprecated aliases in unit_tests and more upgrades yield for loops into yield from generators which are more performance and propagates more information / exceptions from original generator. This is the modern recommended way of forwarding generators.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94309
Approved by: https://github.com/albanD
removes this unused var, the overall buffer comm hook feature is also not being used, we should deprecate / remove it as it is still a private API.
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93128
Approved by: https://github.com/awgu
Allow _apply_optim_in_backward to work with DDP.
Example:
```
dist.init_process_group("nccl", rank=rank, world_size=2)
torch.cuda.set_device(rank)
e = enc().cuda(rank)
_apply_optimizer_in_backward(
optimizer_class=torch.optim.SGD,
params=e.parameters(),
optimizer_kwargs={"lr": 0.03},
)
e = DDP(e, device_ids=[rank])
inp = torch.randn(1, 10, device=rank)
e(inp).sum().backward()
```
Constraints:
1. Custom communication hook not yet supported
2. _apply_optim_in_backward needs to be called _before_ wrapping model in DDP.
3. DDP will remove the gradient hooks _apply_optim_in_backward registers, so these gradient hooks will not be fired and cannot be used.
4. All DDP managed parameters have grads set to None by default once optimizer is applied. There is no support for setting only some parameter grads to None, this must be done manually by user (and DDP_OVERLAPPED_OPTIM_SET_GRADS_TO_NONE=0 needs to be set.)
Differential Revision: [D41329694](https://our.internmc.facebook.com/intern/diff/D41329694/)
**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D41329694/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89194
Approved by: https://github.com/zhaojuanmao
This is a new version of #15648 based on the latest master branch.
Unlike the previous PR where I fixed a lot of the doctests in addition to integrating xdoctest, I'm going to reduce the scope here. I'm simply going to integrate xdoctest, and then I'm going to mark all of the failing tests as "SKIP". This will let xdoctest run on the dashboards, provide some value, and still let the dashboards pass. I'll leave fixing the doctests themselves to another PR.
In my initial commit, I do the bare minimum to get something running with failing dashboards. The few tests that I marked as skip are causing segfaults. Running xdoctest results in 293 failed, 201 passed tests. The next commits will be to disable those tests. (unfortunately I don't have a tool that will insert the `#xdoctest: +SKIP` directive over every failing test, so I'm going to do this mostly manually.)
Fixes https://github.com/pytorch/pytorch/issues/71105
@ezyang
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82797
Approved by: https://github.com/ezyang
### Description
Across PyTorch's docstrings, both `callable` and `Callable` for variable types. The Callable should be capitalized as we are referring to the `Callable` type, and not the Python `callable()` function.
### Testing
There shouldn't be any testing required.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82487
Approved by: https://github.com/albanD
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75753
As per the design in https://github.com/pytorch/pytorch/issues/72138,
convert DDP parameters to ReplicatedTensor during its forward pass. Concretely,
this is done as follows:
1) Create a separate `_replicated_tensor_module` which is a copy of self.module
without creating copies of the Tensors themselves.
2) Use `_replicated_tensor_module` instead of `self.module` during the forward
pass.
3) Have a context manager `_ddp_replicated_tensor` to enable this, since
certain edge cases can fail where self.module is changed out of band resulting
in discrepancy between self.module and `_replicated_tensor_module`.
Differential Revision: [D35533736](https://our.internmc.facebook.com/intern/diff/D35533736/)
Approved by: https://github.com/wanchaol, https://github.com/rohan-varma
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74063
Address the issue https://github.com/pytorch/pytorch/issues/66229 as part of BE effort.
Basically:
1. We remove the stale comment which confuses users.
2. Add more unit tests to test the forward/backward hook working for DDP.
ghstack-source-id: 151463380
Test Plan: CI
Reviewed By: rohan-varma
Differential Revision: D34800830
fbshipit-source-id: 21133209323b2b5eda0dd6472f6309d4fb779b97
(cherry picked from commit b9b165c8305572128395daffafc13fcac8b85e29)
