raiseRuntimeError("master_params recieved a gradient in the backward pass!")
defprep_param_lists(model,flat_master=False):
"""
Creates a list of FP32 master parameters for a given model, as in
`Training Neural Networks with Mixed Precision: Real Examples`_.
Args:
model (torch.nn.Module): Existing Pytorch model
flat_master (bool, optional, default=False): Flatten the master parameters into a single tensor, as a performance optimization.
Returns:
A tuple (``model_params``, ``master_params``). ``model_params`` is a list of the model's parameters for later use with :func:`model_grads_to_master_grads` and :func:`master_params_to_model_params`. ``master_params`` is a list of FP32 master gradients. If ``flat_master=True``, ``master_params`` will be a list with one element.
Currently, if ``flat_master=True``, all the model's parameters must be the same type. If the model has parameters of different types, use ``flat_master=False``, or use :class:`FP16_Optimizer`.
.. _`Training Neural Networks with Mixed Precision: Real Examples`:
model_params: List of model parameters created by :func:`prep_param_lists`.
master_params: List of FP32 master parameters created by :func:`prep_param_lists`. If ``master_params`` was created with ``flat_master=True``, ``flat_master=True`` should also be supplied to :func:`model_grads_to_master_grads`.
"""
ifflat_master:
# The flattening may incur one more deep copy than is necessary.
model_params: List of model parameters created by :func:`prep_param_lists`.
master_params: List of FP32 master parameters created by :func:`prep_param_lists`. If ``master_params`` was created with ``flat_master=True``, ``flat_master=True`` should also be supplied to :func:`master_params_to_model_params`.
# item() is a recent addition, so this helps with backward compatibility.
defto_python_float(t):
ifhasattr(t,'item'):
returnt.item()
else:
returnt[0]
classLossScaler:
"""
Class that manages a static loss scale. This class is intended to interact with
:class:`FP16_Optimizer`, and should not be directly manipulated by the user.
Use of :class:`LossScaler` is enabled via the ``static_loss_scale`` argument to
:class:`FP16_Optimizer`'s constructor.
Args:
scale (float, optional, default=1.0): The loss scale.
"""
def__init__(self,scale=1):
self.cur_scale=scale
# `params` is a list / generator of torch.Variable
defhas_overflow(self,params):
returnFalse
# `x` is a torch.Tensor
def_has_inf_or_nan(x):
returnFalse
defupdate_scale(self,overflow):
pass
@property
defloss_scale(self):
returnself.cur_scale
defscale_gradient(self,module,grad_in,grad_out):
_overflow_buf=torch.cuda.IntTensor([0])
multi_tensor_applier(amp_C.multi_tensor_scale,
_overflow_buf,
[grad_in,grad_in],
self.loss_scale)
returngrad_in
defbackward(self,loss,retain_graph=False):
scaled_loss=loss*self.loss_scale
scaled_loss.backward(retain_graph=retain_graph)
classDynamicLossScaler:
"""
Class that manages dynamic loss scaling. It is recommended to use :class:`DynamicLossScaler`
indirectly, by supplying ``dynamic_loss_scale=True`` to the constructor of
:class:`FP16_Optimizer`. However, it's important to understand how :class:`DynamicLossScaler`
operates, because the default options can be changed using the
the ``dynamic_loss_args`` argument to :class:`FP16_Optimizer`'s constructor.
Loss scaling is designed to combat the problem of underflowing gradients encountered at long
times when training fp16 networks. Dynamic loss scaling begins by attempting a very high loss
scale. Ironically, this may result in OVERflowing gradients. If overflowing gradients are
encountered, :class:`DynamicLossScaler` informs :class:`FP16_Optimizer` that an overflow has
occurred.
:class:`FP16_Optimizer` then skips the update step for this particular iteration/minibatch,
and :class:`DynamicLossScaler` adjusts the loss scale to a lower value.
If a certain number of iterations occur without overflowing gradients detected,
:class:`DynamicLossScaler` increases the loss scale once more.
In this way :class:`DynamicLossScaler` attempts to "ride the edge" of
always using the highest loss scale possible without incurring overflow.
Args:
init_scale (float, optional, default=2**32): Initial loss scale attempted by :class:`DynamicLossScaler.`
scale_factor (float, optional, default=2.0): Factor used when adjusting the loss scale. If an overflow is encountered, the loss scale is readjusted to loss scale/``scale_factor``. If ``scale_window`` consecutive iterations take place without an overflow, the loss scale is readjusted to loss_scale*``scale_factor``.
scale_window (int, optional, default=1000): Number of consecutive iterations without an overflow to wait before increasing the loss scale.