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# Copyright (c) 2022, NVIDIA CORPORATION. All rights reserved.
"""Megatron grad scaler."""
from abc import ABC
from abc import abstractmethod
import torch
class MegatronGradScaler(ABC):
def __init__(self, initial_scale):
"""Initialize scale value with the input initial scale."""
assert initial_scale > 0.0
self._scale = torch.cuda.FloatTensor([initial_scale])
@property
def scale(self):
return self._scale
@property
def inv_scale(self):
return self._scale.double().reciprocal().float()
@abstractmethod
def update(self, found_inf):
pass
@abstractmethod
def state_dict(self):
pass
@abstractmethod
def load_state_dict(self, state_dict):
pass
class ConstantGradScaler(MegatronGradScaler):
def update(self, found_inf):
pass
def state_dict(self):
return dict()
def load_state_dict(self, state_dict):
pass
class DynamicGradScaler(MegatronGradScaler):
def __init__(self, initial_scale, min_scale,
growth_factor, backoff_factor,
growth_interval, hysteresis):
""""Grad scaler with dynamic scale that gets adjusted
during training."""
super(DynamicGradScaler, self).__init__(initial_scale)
# Lower bound on the scale.
assert min_scale > 0.0
assert min_scale <= initial_scale
self.min_scale = torch.cuda.FloatTensor([min_scale])
# Growth and backoff factors for the scale.
assert growth_factor > 1.0
self.growth_factor = torch.cuda.FloatTensor([growth_factor])
assert backoff_factor < 1.0
assert backoff_factor > 0.0
self.backoff_factor = torch.cuda.FloatTensor([backoff_factor])
# Interval over which if we don't see any inf/nan,
# we will scale the grad scale by the growth factor.
assert growth_interval > 0
self.growth_interval = growth_interval
# Number of inf/nans we should see before scaling down
# the grad scale by the backoff factor.
assert hysteresis > 0
self.hysteresis = hysteresis
# Trackers.
self._growth_tracker = 0
self._hysteresis_tracker = self.hysteresis
def update(self, found_inf):
# If we have an inf/nan, growth tracker is set to 0
# and hysterisis tracker is reduced by 1.
if found_inf:
self._growth_tracker = 0
self._hysteresis_tracker -= 1
# Now if we are out of hysteresis count, scale down the loss.
if self._hysteresis_tracker <= 0:
self._scale = torch.max(self._scale * self.backoff_factor,
self.min_scale)
else:
# If there is no nan/inf, increment the growth tracker.
self._growth_tracker += 1
# If we have had enough consequitive intervals with no nan/inf:
if self._growth_tracker == self.growth_interval:
# Reset the tracker and hysteresis trackers,
self._growth_tracker = 0
self._hysteresis_tracker = self.hysteresis
# and scale up the loss scale.
self._scale = self._scale * self.growth_factor
def state_dict(self):
state_dict = {}
state_dict['scale'] = self._scale
state_dict['growth_tracker'] = self._growth_tracker
state_dict['hysteresis_tracker'] = self._hysteresis_tracker
return state_dict
def load_state_dict(self, state_dict):
self._scale = state_dict['scale'].cuda(torch.cuda.current_device())
self._growth_tracker = state_dict['growth_tracker']
self._hysteresis_tracker = state_dict['hysteresis_tracker']
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