This PR is greatly simplified now that it stacked on top of a PR that builds with distributed always. We only need to stub functions that may not be defined due to a backend not being enabled.
Signed-off-by: Edward Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/159889
Approved by: https://github.com/wconstab
ghstack dependencies: #160449
We don't create new PGs when doing slicing in DeviceMesh so it is relatively safe to relax the requirement of one can only do slicing from root mesh. But this does come with caveat when it is asymmetric, for example, only some have the sliced out submesh, for example. So aside from removing the requirement we also add a warning here.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/158899
Approved by: https://github.com/wz337
Fixed error message:
On main:
```
KeyError: ("Invalid mesh_dim_names ('dp_shard', 'dp_shard') specified. ", 'Found mesh dim indices to slice: [(1,), (1,)]. ', 'Mesh dim indices should be in ascending order.')
```
On PR:
```
KeyError: Invalid mesh_dim_names ('dp_shard', 'dp_shard') specified. Found mesh dim indices to slice: [(1,), (1,)]. Mesh dim indices should be in ascending order.'
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/157096
Approved by: https://github.com/Skylion007
as titled, this PR improves the device selection logic when user did not
set the device before calling the DeviceMesh constructor, as a device
manager, DeviceMesh should try to set the device for users in a good
way.
The behavior of set_device before:
* If user call init_process_group to init a world process group, we assume user already called set_device and we don't set the device for the user
* If user does not init a world process group by themselves, we init a world process group for the user and follow a heuristic to set the device.
This is ok but sometimes the set_device heuristic wouldn't work well (i.e. if user use TORCH_CUDA_VISBILE_DEVICES
So this PR improves the device selection logic to:
* If the default cuda context is initialized by the time we init DeviceMesh, then we assume user must called some cuda operation before therefore must have selected the device by themselves
* If not the above, then we check if envvars have "LOCAL_RANK" and "WORLD_SIZE" from the launcher (i.e. torchrun), if so, we use "LOCAL_RANK" to set the device for the current process, which is a very standard practice. (This solves the TORCH_CUDA_VISBILE_DEVICES issue)
* If not above, then we throw warning to users about situation, and fallback to the old heuristic.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/150897
Approved by: https://github.com/tianyu-l
ghstack dependencies: #150898
**Summary**
This PR fixes a calculation miss in DeviceMesh's create_sub_mesh().
**Error Description**
When users call `device_mesh["dim0", "dim1", "dim2", "dim3"]`, it creates a slice of mesh or we call it "submesh". Users can also slice a submesh from a flattened mesh. For example:
```
flattened_mesh = device_mesh["dim0", "dim1", "dim2"]._flatten("dim0-2")
alias_flattened_mesh = device_mesh["dim0-2"] # this mesh slice leads to error in current impl
```
It triggers the error in the size calculation `reduce(lambda, mesh_dim)` happening in `create_sub_mesh`:
```
IndexError: Dimension out of range (expected to be in range of [-4, 3], but got 4)
```
**Fix**
The usage of lambda is wrong, for `lambda x, y`, the x is the accumulated value while `y` is the iterator value.
**Test**
`pytest test/distributed/test_device_mesh.py -s -k test_flatten_mesh_4d`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/138945
Approved by: https://github.com/wz337
Use `split_group()` to create sub_groups for nccl backend if the default pg is eagerly initialized. Otherwise, it will still go through the normal lazy init process and call `new_group()` instead.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/138129
Approved by: https://github.com/kwen2501
As `backend`, `pg_options`, and `group_desc` are the same for each mesh dimension, we don't need to get or create these args for `new_group` multiple times. This PR moves it from the inner loop of the subgroup creation (each subgroup ranks of each mesh dimension) to the outer loop (each mesh_dimension).
For example, given we have a 2 * 4 DeviceMesh, we are re-creating the variables `backend`, `pg_options`, and `group_desc` 2*4 = 8 times. After the change, we only create these variables once per mesh dimension, which is 2 times.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/138117
Approved by: https://github.com/kwen2501
We introduced the dispatchable backend for a ProcessGroup and collective in https://github.com/pytorch/pytorch/issues/86225. This PR is a follow-up cleanup to clean up the option of a ProcessGroup and ask users to either set timeout or backend later on or directly create backend after creating a PG.
Also PGNCCL is using option class from ProcessGroup but we actually should use Option from backend class. So this PR is to make the type or name to be aligned with what we are doing in cpp side. I don't change the signature for the public API, so they still use args named "pg_options"
We need to make changes to the test to make it aligned with the change.
This is try to reland D62008954 by fixing internal errors.
Differential Revision: [D62483294](https://our.internmc.facebook.com/intern/diff/D62483294/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/135653
Approved by: https://github.com/wz337, https://github.com/H-Huang
We introduced the dispatchable backend for a ProcessGroup and collective in https://github.com/pytorch/pytorch/issues/86225. This PR is a follow-up cleanup to clean up the option of a ProcessGroup and ask users to either set timeout or backend later on or directly create backend after creating a PG.
Also PGNCCL is using option class from ProcessGroup but we actually should use Option from backend class. So this PR is to make the type or name to be aligned with what we are doing in cpp side. I don't change the signature for the public API, so they still use args named "pg_options"
We need to make changes to the test to make it aligned with the change.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/132931
Approved by: https://github.com/H-Huang
If a mesh_dim_name is given, we will use the given mesh_dim_name to name the new flattened dim.
Otherwise, the default is a string concatentaing the mesh_dim_names of the given submesh with each mesh_dim_name separated by "_".
For example, if we have a 3D mesh DeviceMesh([[[0, 1], [2, 3]], [[4, 5], [6, 7]]], mesh_dim_names=("dp", "cp", "tp")), calling mesh_3d["dp", "cp"]._flatten() will create a 1D submesh DeviceMesh([0, 1, 2, 3], mesh_dim_names=("dp_cp",)) on rank 0, 1, 2, 3 and a 1D submesh DeviceMesh([4, 5, 6, 7], mesh_dim_names=("dp_cp",)) on rank 4, 5, 6, 7.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/134048
Approved by: https://github.com/fegin
ghstack dependencies: #133838, #133839
Add DeviceMesh slicing support such that we could do the following:
```
mesh_3d = init_device_mesh(
self.device_type, (2, 2, 2), mesh_dim_names=("replicate", "shard", "cp")
)
shard_cp_mesh = mesh_3d["shard", "cp"]._flatten()
hsdp_mesh = mesh_3d["replicate", "shard_cp"]
# we can get the corresponding group of the flatten mesh through
group = shard_cp_mesh.get_group()
# or
group = mesh_3d["shard_cp"].get_group()
# or
mesh_3d.get_group(mesh_dim="shard_cp")
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/133839
Approved by: https://github.com/fegin
ghstack dependencies: #133838
```
# supposed we have a 3d mesh
mesh_3d = init_device_mesh("cuda", (2,2,2), mesh_dim_names=("dp", "cp", "tp")
dp_cp_mesh = mesh_3d["dp", "cp"]._flatten()
"""
then we would have
flatten_name_to_root_dims[mesh_3d]: {
"dp_cp": (0, 1)
}
"""
```
We need this information to validate the order mesh slice including flatten mesh dim.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/133838
Approved by: https://github.com/fegin
More context in [#132471](https://github.com/pytorch/pytorch/issues/132471) and https://github.com/pytorch/pytorch/issues/132366.
TLDR:
When cuda is available and users move tensors to cuda, we cannot really reuse the default pg if default pg is gloo, as lots of collectives are not supported on gloo for cuda tensors. For example, `dtensor.full_tensor()` would result in a mysterious SIGTERM when all_gather a cuda tensor using gloo. Without the change in this PR, users would have to know the context and explicitly move the cuda tensor to cpu before invoking most collectives, which I think is not so ideal UX.
Therefore, given most collectives are not supported on gloo for cuda tensors, we should init a new pg if the default pg is gloo when torch.cuda.is_available() and device_type is cuda.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/132709
Approved by: https://github.com/awgu, https://github.com/wanchaol
Previously, when we slice out a submesh from a mesh, we assign the mesh as the parent mesh of the submesh. In this case, when we have a 3D mesh topology, the parent mesh of a 1D mesh sliced out from the 3D mesh is different from the parent mesh of the same 1D mesh sliced out from the 2D submesh of the 3D mesh. For example:
```
mesh_3d = init_device_mesh("cuda", (2,2,2), ("dim0", "dim1", "dim2"))
mesh_dim0 = mesh_3d["dim0"]
mesh_2d = mesh_2d["dim0", "dim1"]
mesh_dim0_2 = mesh_2d["dim0_2"]
# This would evaluate to be True
print(_mesh_resources.get_parent_mesh(mesh_dim0) != _mesh_resources.get_parent_mesh(mesh_dim0))
```
We can always reconstruct the mesh needed from the mesh dim names, as long as two dims come from the same root. For simplicity, we do not see the necessity of building a tree structure to represent child-parent relationship. Therefore, we are replacing the parent mesh concept with a root mesh concept in `_MeshEnv` so we would have:
```
mesh_3d = init_device_mesh("cuda", (2,2,2), ("dim0", "dim1", "dim2"))
mesh_dim0 = mesh_3d["dim0"]
mesh_2d = mesh_2d["dim0", "dim1"]
mesh_dim0_2 = mesh_2d["dim0_2"]
# This would evaluate to be True
print(_mesh_resources.get_root_mesh(mesh_dim0) == _mesh_resources.get_root_mesh(mesh_dim0))
```
With this change, we will have two types of meshes in an environment.
1. `device_mesh != _mesh_resources.get_root_mesh(device_mesh)` means that the device_mesh is created by slicing.
2. `device_mesh == _mesh_resources.get_root_mesh(device_mesh)` means that the device_mesh is a root mesh not created through slicing.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/132339
Approved by: https://github.com/wanchaol
ghstack dependencies: #132310, #132311
