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import warnings
import functools
from typing import Union, Iterable, List, Dict, Tuple, Optional, cast
import torch
from torch import Tensor
from torch.utils._foreach_utils import _group_tensors_by_device_and_dtype, _has_foreach_support, _device_has_foreach_support
_tensor_or_tensors = Union[torch.Tensor, Iterable[torch.Tensor]]
__all__ = ['clip_grad_norm_', 'clip_grad_norm', 'clip_grad_value_']
def _no_grad(func):
"""
This wrapper is needed to avoid a circular import when using @torch.no_grad on the exposed functions
clip_grad_norm_ and clip_grad_value_ themselves.
"""
def _no_grad_wrapper(*args, **kwargs):
with torch.no_grad():
return func(*args, **kwargs)
functools.update_wrapper(_no_grad_wrapper, func)
return _no_grad_wrapper
@_no_grad
def clip_grad_norm_(
parameters: _tensor_or_tensors, max_norm: float, norm_type: float = 2.0,
error_if_nonfinite: bool = False, foreach: Optional[bool] = None) -> torch.Tensor:
r"""Clip the gradient norm of an iterable of parameters.
The norm is computed over all gradients together, as if they were
concatenated into a single vector. Gradients are modified in-place.
Args:
parameters (Iterable[Tensor] or Tensor): an iterable of Tensors or a
single Tensor that will have gradients normalized
max_norm (float): max norm of the gradients
norm_type (float): type of the used p-norm. Can be ``'inf'`` for
infinity norm.
error_if_nonfinite (bool): if True, an error is thrown if the total
norm of the gradients from :attr:`parameters` is ``nan``,
``inf``, or ``-inf``. Default: False (will switch to True in the future)
foreach (bool): use the faster foreach-based implementation.
If ``None``, use the foreach implementation for CUDA and CPU native tensors and silently
fall back to the slow implementation for other device types.
Default: ``None``
Returns:
Total norm of the parameter gradients (viewed as a single vector).
"""
if isinstance(parameters, torch.Tensor):
parameters = [parameters]
grads = [p.grad for p in parameters if p.grad is not None]
max_norm = float(max_norm)
norm_type = float(norm_type)
if len(grads) == 0:
return torch.tensor(0.)
first_device = grads[0].device
grouped_grads: Dict[Tuple[torch.device, torch.dtype], Tuple[List[List[Tensor]], List[int]]] \
= _group_tensors_by_device_and_dtype([grads]) # type: ignore[assignment]
norms: List[Tensor] = []
for ((device, _), ([device_grads], _)) in grouped_grads.items(): # type: ignore[assignment]
if (
(foreach is None and _has_foreach_support(device_grads, device))
or (foreach and _device_has_foreach_support(device))
):
norms.extend(torch._foreach_norm(device_grads, norm_type))
elif foreach:
raise RuntimeError(f'foreach=True was passed, but can\'t use the foreach API on {device.type} tensors')
else:
norms.extend([torch.linalg.vector_norm(g, norm_type) for g in device_grads])
total_norm = torch.linalg.vector_norm(torch.stack([norm.to(first_device) for norm in norms]), norm_type)
if error_if_nonfinite and torch.logical_or(total_norm.isnan(), total_norm.isinf()):
raise RuntimeError(
f'The total norm of order {norm_type} for gradients from '
'`parameters` is non-finite, so it cannot be clipped. To disable '
'this error and scale the gradients by the non-finite norm anyway, '
'set `error_if_nonfinite=False`')
clip_coef = max_norm / (total_norm + 1e-6)
# Note: multiplying by the clamped coef is redundant when the coef is clamped to 1, but doing so
# avoids a `if clip_coef < 1:` conditional which can require a CPU <=> device synchronization
# when the gradients do not reside in CPU memory.
clip_coef_clamped = torch.clamp(clip_coef, max=1.0)
for ((device, _), ([device_grads], _)) in grouped_grads.items(): # type: ignore[assignment]
if (
(foreach is None and _has_foreach_support(device_grads, device))
or (foreach and _device_has_foreach_support(device))
):
torch._foreach_mul_(device_grads, clip_coef_clamped.to(device))
elif foreach:
raise RuntimeError(f'foreach=True was passed, but can\'t use the foreach API on {device.type} tensors')
else:
clip_coef_clamped_device = clip_coef_clamped.to(device)
for g in device_grads:
g.mul_(clip_coef_clamped_device)
return total_norm
def clip_grad_norm(
parameters: _tensor_or_tensors, max_norm: float, norm_type: float = 2.,
error_if_nonfinite: bool = False, foreach: Optional[bool] = None) -> torch.Tensor:
r"""Clip the gradient norm of an iterable of parameters.
.. warning::
This method is now deprecated in favor of
:func:`torch.nn.utils.clip_grad_norm_`.
"""
warnings.warn("torch.nn.utils.clip_grad_norm is now deprecated in favor "
"of torch.nn.utils.clip_grad_norm_.", stacklevel=2)
return clip_grad_norm_(parameters, max_norm, norm_type, error_if_nonfinite, foreach)
@_no_grad
def clip_grad_value_(parameters: _tensor_or_tensors, clip_value: float, foreach: Optional[bool] = None) -> None:
r"""Clip the gradients of an iterable of parameters at specified value.
Gradients are modified in-place.
Args:
parameters (Iterable[Tensor] or Tensor): an iterable of Tensors or a
single Tensor that will have gradients normalized
clip_value (float): maximum allowed value of the gradients.
The gradients are clipped in the range
:math:`\left[\text{-clip\_value}, \text{clip\_value}\right]`
foreach (bool): use the faster foreach-based implementation
If ``None``, use the foreach implementation for CUDA and CPU native tensors and
silently fall back to the slow implementation for other device types.
Default: ``None``
"""
if isinstance(parameters, torch.Tensor):
parameters = [parameters]
clip_value = float(clip_value)
grads = [p.grad for p in parameters if p.grad is not None]
grouped_grads = _group_tensors_by_device_and_dtype([grads])
for ((device, _), ([grads], _)) in grouped_grads.items(): # type: ignore[assignment]
if (
(foreach is None and _has_foreach_support(cast(List[Tensor], grads), device=device))
or (foreach and _device_has_foreach_support(device))
):
torch._foreach_clamp_min_(cast(List[Tensor], grads), -clip_value)
torch._foreach_clamp_max_(cast(List[Tensor], grads), clip_value)
elif foreach:
raise RuntimeError(f'foreach=True was passed, but can\'t use the foreach API on {device.type} tensors')
else:
for grad in grads:
cast(Tensor, grad).clamp_(min=-clip_value, max=clip_value)
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