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# Copyright (c) Microsoft Corporation.
# SPDX-License-Identifier: Apache-2.0
# DeepSpeed Team
"""
Copyright NVIDIA/apex
This file is adapted from NVIDIA/apex/optimizer/fused_adam and implements the LAMB optimizer
"""
import types
import torch
from deepspeed.ops.op_builder import FusedLambBuilder
class FusedLamb(torch.optim.Optimizer):
"""Implements the LAMB algorithm. Currently GPU-only.
LAMB was proposed in `Large Batch Optimization for Deep Learning: Training BERT in 76 minutes.
https://arxiv.org/abs/1904.00962
Arguments:
params (iterable): iterable of parameters to optimize or dicts defining
parameter groups.
lr (float, optional): learning rate. (default: 1e-3)
bias_correction (bool, optional): bias correction (default: True)
betas (Tuple[float, float], optional): coefficients used for computing
running averages of gradient and its square. (default: (0.9, 0.999))
eps (float, optional): term added to the denominator to improve
numerical stability. (default: 1e-8)
eps_inside_sqrt (boolean, optional): in the 'update parameters' step,
adds eps to the bias-corrected second moment estimate before
evaluating square root instead of adding it to the square root of
second moment estimate as in the original paper. (default: False)
weight_decay (float, optional): weight decay (L2 penalty) (default: 0)
max_grad_norm (float, optional): value used to clip global grad norm
(default: 0.0)
max_coeff(float, optional): maximum value of the lamb coefficient (default: 10.0)
min_coeff(float, optional): minimum value of the lamb coefficient (default: 0.01)
amsgrad (boolean, optional): NOT SUPPORTED in FusedLamb!
"""
def __init__(self,
params,
lr=1e-3,
bias_correction=True,
betas=(0.9, 0.999),
eps=1e-8,
eps_inside_sqrt=False,
weight_decay=0.,
max_grad_norm=0.,
max_coeff=10.0,
min_coeff=0.01,
amsgrad=False):
self.fused_lamb_cuda = FusedLambBuilder().load()
if amsgrad:
raise RuntimeError('FusedLamb does not support the AMSGrad variant.')
defaults = dict(lr=lr,
bias_correction=bias_correction,
betas=betas,
eps=eps,
weight_decay=weight_decay,
max_grad_norm=max_grad_norm,
max_coeff=max_coeff,
min_coeff=min_coeff)
super(FusedLamb, self).__init__(params, defaults)
self.eps_mode = 0 if eps_inside_sqrt else 1
self.lamb_coeffs = []
def step(self, closure=None, grads=None, output_params=None, scale=1., grad_norms=None):
"""Performs a single optimization step.
Arguments:
closure (callable, optional): A closure that reevaluates the model
and returns the loss.
grads (list of tensors, optional): weight gradient to use for the
optimizer update. If gradients have type torch.half, parameters
are expected to be in type torch.float. (default: None)
output params (list of tensors, optional): A reduced precision copy
of the updated weights written out in addition to the regular
updated weights. Have to be of same type as gradients. (default: None)
scale (float, optional): factor to divide gradient tensor values
by before applying to weights. (default: 1)
"""
loss = None
if closure is not None:
loss = closure()
if grads is None:
grads_group = [None] * len(self.param_groups)
# backward compatibility
# assuming a list/generator of parameter means single group
elif isinstance(grads, types.GeneratorType):
grads_group = [grads]
elif type(grads[0]) != list:
grads_group = [grads]
else:
grads_group = grads
if output_params is None:
output_params_group = [None] * len(self.param_groups)
elif isinstance(output_params, types.GeneratorType):
output_params_group = [output_params]
elif type(output_params[0]) != list:
output_params_group = [output_params]
else:
output_params_group = output_params
if grad_norms is None:
grad_norms = [None] * len(self.param_groups)
#remove the previous coeffs
del self.lamb_coeffs[:]
for group, grads_this_group, output_params_this_group, grad_norm_group in zip(
self.param_groups, grads_group, output_params_group, grad_norms):
if grads_this_group is None:
grads_this_group = [None] * len(group['params'])
if output_params_this_group is None:
output_params_this_group = [None] * len(group['params'])
if grad_norm_group is None:
grad_norm_group = [None] * len(group['params'])
elif not isinstance(grad_norm_group, list):
grad_norm_group = [grad_norm_group]
bias_correction = 1 if group['bias_correction'] else 0
for p, grad, output_param, grad_norm in zip(group['params'], grads_this_group, output_params_this_group,
grad_norm_group):
# compute combined scale factor for this group
combined_scale = scale
if group['max_grad_norm'] > 0:
# norm is in fact norm*scale
clip = ((grad_norm / scale) + 1e-6) / group['max_grad_norm']
if clip > 1:
combined_scale = clip * scale
#note: p.grad should not ever be set for correct operation of mixed precision optimizer that sometimes sends None gradients
if p.grad is None and grad is None:
continue
if grad is None:
grad = p.grad.data
if grad.is_sparse:
raise RuntimeError('FusedLamb does not support sparse gradients')
state = self.state[p]
# State initialization
if len(state) == 0:
state['step'] = 0
# Exponential moving average of gradient values
state['exp_avg'] = torch.zeros_like(p.data)
# Exponential moving average of squared gradient values
state['exp_avg_sq'] = torch.zeros_like(p.data)
exp_avg, exp_avg_sq = state['exp_avg'], state['exp_avg_sq']
beta1, beta2 = group['betas']
max_coeff = group['max_coeff']
min_coeff = group['min_coeff']
state['step'] += 1
out_p = torch.tensor([], dtype=torch.float) if output_param is None else output_param
lamb_coeff = self.fused_lamb_cuda.lamb(p.data, out_p, exp_avg, exp_avg_sq, grad, group['lr'], beta1,
beta2, max_coeff, min_coeff, group['eps'], combined_scale,
state['step'], self.eps_mode, bias_correction,
group['weight_decay'])
self.lamb_coeffs.append(lamb_coeff)
return loss
def get_lamb_coeffs(self):
lamb_coeffs = [lamb_coeff.item() for lamb_coeff in self.lamb_coeffs]
return lamb_coeffs
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