This PR implements _allgather_base, reduce_scatter, and _reduce_scatter_base in the MPI backend (ProcessGroupMPI), enabling support for Fully Sharded Data Parallel (FSDP) in environments that use MPI for distributed communication.
### Context
As noted in https://github.com/pytorch/pytorch/issues/85628, FSDP currently supports only the NCCL backend. Due to this limitation, FSDP cannot run on legacy HPC environments or clusters that rely on MPI.
By implementing just these three collective operations, we can enable FSDP to work with the MPI backend. These collectives are implemented in a similar manner to existing operations such as allgather.
### Testing
We validated this PR using pytorch/build/bin/ProcessGroupMPITest with OpenMPI, and all tests passed successfully.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/150162
Approved by: https://github.com/H-Huang
Headers under torch/csrc/distributed may be referened with relative path, e.g., "<c10d/...>". However, relative path cannot be gracefully handled by Meta internal build when the NCCL PG is hipified to support AMD/RCCL because the "hipified" header files are generated in other directories. Moreover, using absolute path for header inclusion is the state-of-the-art in most components in Pytorch. Thus, this patch refactors all header paths in torch/csrc/distributed to be absolute.
See D39835774 for more details about Meta internal complication.
**How to test**: commit 9e5d199 removes -I./torch/csrc/distributed in compile options. Thus use it to verify we don't miss any relative path use of torch/csrc/distributed headers.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85780
Approved by: https://github.com/kumpera, https://github.com/huydhn
Headers under torch/csrc/distributed may be referened with relative path, e.g., "<c10d/...>". However, relative path cannot be gracefully handled by Meta internal build when the NCCL PG is hipified to support AMD/RCCL because the "hipified" header files are generated in other directories. Moreover, using absolute path for header inclusion is the state-of-the-art in most components in Pytorch. Thus, this patch refactors all header paths in torch/csrc/distributed to be absolute.
See D39835774 for more details about Meta internal complication.
**How to test**: commit 9e5d199 removes -I./torch/csrc/distributed in compile options. Thus use it to verify we don't miss any relative path use of torch/csrc/distributed headers.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85780
Approved by: https://github.com/kumpera
### Changes
- Move ProcessGroup::Work into its own class and update all the references to it / header includes.
#### Motivation
In the future PRs we will repurpose ProcessGroup to instead contain a list of Backends (ProcessGroupNCCL/Gloo/UCC) and perform dispatching to them based on tensor type. This change is prevent a circular dependency with ProcessGroup depending on Backend and Backend depending on ProcessGroup::Work.
Differential Revision: [D38839212](https://our.internmc.facebook.com/intern/diff/D38839212)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83680
Approved by: https://github.com/kwen2501
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60543
Since now c10d is part of libtorch, it would also be nice if the sources lived all in one place.
ghstack-source-id: 132306292
Test Plan: It builds
Reviewed By: cbalioglu
Differential Revision: D29062002
fbshipit-source-id: d9e1301e9d73e1643fa0f0119cd2d618f1ad52e6
