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loss_scaler.py
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loss_scaler.py
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import torch
class LossScaler:
def __init__(self, scale=1):
self.cur_scale = scale
# `params` is a list / generator of torch.Variable
def has_overflow(self, params):
return False
# `x` is a torch.Tensor
def _has_inf_or_nan(x):
return False
# `overflow` is boolean indicating whether we overflowed in gradient
def update_scale(self, overflow):
pass
@property
def loss_scale(self):
return self.cur_scale
def scale_gradient(self, module, grad_in, grad_out):
return tuple(self.loss_scale * g for g in grad_in)
def backward(self, loss):
scaled_loss = loss*self.loss_scale
scaled_loss.backward()
class DynamicLossScaler:
def __init__(self,
init_scale=2**32,
scale_factor=2.,
scale_window=1000):
self.cur_scale = init_scale
self.cur_iter = 0
self.last_overflow_iter = -1
self.scale_factor = scale_factor
self.scale_window = scale_window
# `params` is a list / generator of torch.Variable
def has_overflow(self, params):
# return False
for p in params:
if p.grad is not None and DynamicLossScaler._has_inf_or_nan(p.grad.data):
return True
return False
# `x` is a torch.Tensor
def _has_inf_or_nan(x):
cpu_sum = float(x.float().sum())
if cpu_sum == float('inf') or cpu_sum == -float('inf') or cpu_sum != cpu_sum:
return True
return False
# `overflow` is boolean indicating whether we overflowed in gradient
def update_scale(self, overflow):
if overflow:
#self.cur_scale /= self.scale_factor
self.cur_scale = max(self.cur_scale/self.scale_factor, 1)
self.last_overflow_iter = self.cur_iter
else:
if (self.cur_iter - self.last_overflow_iter) % self.scale_window == 0:
self.cur_scale *= self.scale_factor
# self.cur_scale = 1
self.cur_iter += 1
@property
def loss_scale(self):
return self.cur_scale
def scale_gradient(self, module, grad_in, grad_out):
return tuple(self.loss_scale * g for g in grad_in)
def backward(self, loss):
scaled_loss = loss*self.loss_scale
scaled_loss.backward()
##############################################################
# Example usage below here -- assuming it's in a separate file
##############################################################
if __name__ == "__main__":
import torch
from torch.autograd import Variable
from dynamic_loss_scaler import DynamicLossScaler
# N is batch size; D_in is input dimension;
# H is hidden dimension; D_out is output dimension.
N, D_in, H, D_out = 64, 1000, 100, 10
# Create random Tensors to hold inputs and outputs, and wrap them in Variables.
x = Variable(torch.randn(N, D_in), requires_grad=False)
y = Variable(torch.randn(N, D_out), requires_grad=False)
w1 = Variable(torch.randn(D_in, H), requires_grad=True)
w2 = Variable(torch.randn(H, D_out), requires_grad=True)
parameters = [w1, w2]
learning_rate = 1e-6
optimizer = torch.optim.SGD(parameters, lr=learning_rate)
loss_scaler = DynamicLossScaler()
for t in range(500):
y_pred = x.mm(w1).clamp(min=0).mm(w2)
loss = (y_pred - y).pow(2).sum() * loss_scaler.loss_scale
print('Iter {} loss scale: {}'.format(t, loss_scaler.loss_scale))
print('Iter {} scaled loss: {}'.format(t, loss.data[0]))
print('Iter {} unscaled loss: {}'.format(t, loss.data[0] / loss_scaler.loss_scale))
# Run backprop
optimizer.zero_grad()
loss.backward()
# Check for overflow
has_overflow = DynamicLossScaler.has_overflow(parameters)
# If no overflow, unscale grad and update as usual
if not has_overflow:
for param in parameters:
param.grad.data.mul_(1. / loss_scaler.loss_scale)
optimizer.step()
# Otherwise, don't do anything -- ie, skip iteration
else:
print('OVERFLOW!')
# Update loss scale for next iteration
loss_scaler.update_scale(has_overflow)