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7c71d7f32b
This PR adds support for `clip_grad_norm_(foreach=True)` by implementing `aten._foreach_norm.Scalar` and `aten._foreach_mul_.Tensor`. `foreach=True` is required to get competitive performance with `DTensor`. `foreach=True` reduces CPU overhead for Llama-7B from 388 ms to 63 ms. Existing flat-parameter FSDP's `clip_grad_norm_` takes 3 ms on CPU 😢 . Pull Request resolved: https://github.com/pytorch/pytorch/pull/120910 Approved by: https://github.com/wanchaol, https://github.com/janeyx99 ghstack dependencies: #120238
48 lines
2.3 KiB
Python
48 lines
2.3 KiB
Python
from typing import List, Dict, Tuple, Optional
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import torch
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from torch import Tensor
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from torch.autograd.grad_mode import no_grad
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from typing_extensions import TypeAlias
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def _get_foreach_kernels_supported_devices() -> List[str]:
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r"""Return the device type list that supports foreach kernels."""
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return ["cuda", "xpu", torch._C._get_privateuse1_backend_name()]
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def _get_fused_kernels_supported_devices() -> List[str]:
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r"""Return the device type list that supports fused kernels in optimizer."""
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return ["cuda", "xpu", torch._C._get_privateuse1_backend_name()]
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TensorListList: TypeAlias = List[List[Optional[Tensor]]]
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Indices: TypeAlias = List[int]
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# This util function splits tensors into groups by device and dtype, which is useful before sending
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# tensors off to a foreach implementation, which requires tensors to be on one device and dtype.
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# If tensorlistlist contains more than one tensorlist, the following assumptions are made BUT NOT verified:
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# - tensorlists CAN be None
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# - all tensors in the first specified list cannot be None
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# - given an index i, all specified tensorlist[i]s match in dtype and device
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# with_indices (bool, optional): whether to track previous indices as the last list per dictionary entry.
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# It comes in handy if there are Nones or literals in the tensorlists that are getting scattered out.
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# Whereas mutating a tensor in the resulting split-up tensorlists WILL propagate changes back to the
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# original input tensorlists, changing up Nones/literals WILL NOT propagate, and manual propagation
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# may be necessary. Check out torch/optim/sgd.py for an example.
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@no_grad()
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def _group_tensors_by_device_and_dtype(
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tensorlistlist: TensorListList,
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with_indices: bool = False,
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) -> Dict[Tuple[torch.device, torch.dtype], Tuple[TensorListList, Indices]]:
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return {
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(device, getattr(torch, str_dtype)): value
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for (device, str_dtype), value in
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torch._C._group_tensors_by_device_and_dtype(tensorlistlist, with_indices).items()
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}
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def _device_has_foreach_support(device: torch.device) -> bool:
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return device.type in (_get_foreach_kernels_supported_devices() + ["cpu"]) and not torch.jit.is_scripting()
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def _has_foreach_support(tensors: List[Tensor], device: torch.device) -> bool:
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return _device_has_foreach_support(device) and all(t is None or type(t) == torch.Tensor for t in tensors)
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