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losses.py
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losses.py
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# Copyright (c) 2015-present, Facebook, Inc.
# All rights reserved.
"""
Implements the knowledge distillation loss
"""
import torch
from torch.nn import functional as F
class DistillationLoss(torch.nn.Module):
"""
This module wraps a standard criterion and adds an extra knowledge distillation loss by
taking a teacher model prediction and using it as additional supervision.
"""
def __init__(self, base_criterion: torch.nn.Module, teacher_model: torch.nn.Module,
distillation_type: str, alpha: float, tau: float):
super().__init__()
self.base_criterion = base_criterion
self.teacher_model = teacher_model
assert distillation_type in ['none', 'soft', 'hard']
self.distillation_type = distillation_type
self.alpha = alpha
self.tau = tau
def forward(self, inputs, outputs, labels):
"""
Args:
inputs: The original inputs that are feed to the teacher model
outputs: the outputs of the model to be trained. It is expected to be
either a Tensor, or a Tuple[Tensor, Tensor], with the original output
in the first position and the distillation predictions as the second output
labels: the labels for the base criterion
"""
outputs_kd = None
if not isinstance(outputs, torch.Tensor):
# assume that the model outputs a tuple of [outputs, outputs_kd]
outputs, outputs_kd = outputs
base_loss = self.base_criterion(outputs, labels)
if self.distillation_type == 'none':
return base_loss
if outputs_kd is None:
raise ValueError("When knowledge distillation is enabled, the model is "
"expected to return a Tuple[Tensor, Tensor] with the output of the "
"class_token and the dist_token")
# don't backprop throught the teacher
with torch.no_grad():
teacher_outputs = self.teacher_model(inputs)
if self.distillation_type == 'soft':
T = self.tau
# taken from https://github.com/peterliht/knowledge-distillation-pytorch/blob/master/model/net.py#L100
# with slight modifications
distillation_loss = F.kl_div(
F.log_softmax(outputs_kd / T, dim=1),
#We provide the teacher's targets in log probability because we use log_target=True
#(as recommended in pytorch https://github.com/pytorch/pytorch/blob/9324181d0ac7b4f7949a574dbc3e8be30abe7041/torch/nn/functional.py#L2719)
#but it is possible to give just the probabilities and set log_target=False. In our experiments we tried both.
F.log_softmax(teacher_outputs / T, dim=1),
reduction='sum',
log_target=True
) * (T * T) / outputs_kd.numel()
#We divide by outputs_kd.numel() to have the legacy PyTorch behavior.
#But we also experiments output_kd.size(0)
#see issue 61(https://github.com/facebookresearch/deit/issues/61) for more details
elif self.distillation_type == 'hard':
distillation_loss = F.cross_entropy(outputs_kd, teacher_outputs.argmax(dim=1))
loss = base_loss * (1 - self.alpha) + distillation_loss * self.alpha
return loss
class DistillationLoss_bi(torch.nn.Module):
"""
This module wraps a standard criterion and adds an extra knowledge distillation loss by
taking a teacher model prediction and using it as additional supervision.
"""
def __init__(self, base_criterion: torch.nn.Module,
distillation_type: str, alpha: float, tau: float):
super().__init__()
self.base_criterion = base_criterion
# self.teacher_model = teacher_model
assert distillation_type in ['none', 'soft', 'hard']
self.distillation_type = distillation_type
self.alpha = alpha
self.tau = tau
def forward(self, inputs, outputs, labels, teacher_outputs):
"""
Args:
inputs: The original inputs that are feed to the teacher model
outputs: the outputs of the model to be trained. It is expected to be
either a Tensor, or a Tuple[Tensor, Tensor], with the original output
in the first position and the distillation predictions as the second output
labels: the labels for the base criterion
"""
outputs_kd = None
if not isinstance(outputs, torch.Tensor):
# assume that the model outputs a tuple of [outputs, outputs_kd]
outputs, outputs_kd = outputs
base_loss = self.base_criterion(outputs, labels)
if self.distillation_type == 'none':
return base_loss
if outputs_kd is None:
raise ValueError("When knowledge distillation is enabled, the model is "
"expected to return a Tuple[Tensor, Tensor] with the output of the "
"class_token and the dist_token")
# don't backprop throught the teacher
# with torch.no_grad():
# teacher_outputs = self.teacher_model(inputs)
if self.distillation_type == 'soft':
T = self.tau
# taken from https://github.com/peterliht/knowledge-distillation-pytorch/blob/master/model/net.py#L100
# with slight modifications
distillation_loss = F.kl_div(
F.log_softmax(outputs_kd / T, dim=1),
#We provide the teacher's targets in log probability because we use log_target=True
#(as recommended in pytorch https://github.com/pytorch/pytorch/blob/9324181d0ac7b4f7949a574dbc3e8be30abe7041/torch/nn/functional.py#L2719)
#but it is possible to give just the probabilities and set log_target=False. In our experiments we tried both.
F.log_softmax(teacher_outputs / T, dim=1),
reduction='sum',
log_target=True
) * (T * T) / outputs_kd.numel()
#We divide by outputs_kd.numel() to have the legacy PyTorch behavior.
#But we also experiments output_kd.size(0)
#see issue 61(https://github.com/facebookresearch/deit/issues/61) for more details
elif self.distillation_type == 'hard':
distillation_loss = F.cross_entropy(outputs_kd, teacher_outputs.argmax(dim=1))
loss = base_loss * (1 - self.alpha) + distillation_loss * self.alpha
return loss