LAMB optimizer

This commit is contained in:
James Betker 2022-02-15 06:48:13 -07:00
parent 2bdb515068
commit dd585df772
2 changed files with 143 additions and 0 deletions

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@ -0,0 +1,131 @@
"""
Lamb optimizer.
Adapted from original source: https://github.com/cybertronai/pytorch-lamb/blob/master/pytorch_lamb/lamb.py
"""
import collections
import math
import torch
from torch.optim import Optimizer
class Lamb(Optimizer):
r"""Implements Lamb algorithm.
It has been proposed in `Large Batch Optimization for Deep Learning: Training BERT in 76 minutes`_.
Arguments:
params (iterable): iterable of parameters to optimize or dicts defining
parameter groups
lr (float, optional): learning rate (default: 1e-3)
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)
weight_decay (float, optional): weight decay (L2 penalty) (default: 0)
adam (bool, optional): always use trust ratio = 1, which turns this into
Adam. Useful for comparison purposes.
.. _Large Batch Optimization for Deep Learning: Training BERT in 76 minutes:
https://arxiv.org/abs/1904.00962
"""
def __init__(self, params, lr=1e-3, betas=(0.9, 0.999), eps=1e-6,
weight_decay=0, adam=False):
if not 0.0 <= lr:
raise ValueError("Invalid learning rate: {}".format(lr))
if not 0.0 <= eps:
raise ValueError("Invalid epsilon value: {}".format(eps))
if not 0.0 <= betas[0] < 1.0:
raise ValueError("Invalid beta parameter at index 0: {}".format(betas[0]))
if not 0.0 <= betas[1] < 1.0:
raise ValueError("Invalid beta parameter at index 1: {}".format(betas[1]))
defaults = dict(lr=lr, betas=betas, eps=eps,
weight_decay=weight_decay)
self.adam = adam
super(Lamb, self).__init__(params, defaults)
def step(self, closure=None):
"""Performs a single optimization step.
Arguments:
closure (callable, optional): A closure that reevaluates the model
and returns the loss.
"""
loss = None
if closure is not None:
loss = closure()
for group in self.param_groups:
for p in group['params']:
if p.grad is None:
continue
grad = p.grad.data
if grad.is_sparse:
raise RuntimeError('Lamb does not support sparse gradients, consider SparseAdam instad.')
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']
state['step'] += 1
# Decay the first and second moment running average coefficient
# m_t
exp_avg.mul_(beta1).add_(grad, alpha=1 - beta1)
# v_t
exp_avg_sq.mul_(beta2).addcmul_(grad, grad, value=1 - beta2)
# Paper v3 does not use debiasing.
# bias_correction1 = 1 - beta1 ** state['step']
# bias_correction2 = 1 - beta2 ** state['step']
# Apply bias to lr to avoid broadcast.
step_size = group['lr'] # * math.sqrt(bias_correction2) / bias_correction1
weight_norm = p.data.pow(2).sum().sqrt().clamp(0, 10)
adam_step = exp_avg / exp_avg_sq.sqrt().add(group['eps'])
if group['weight_decay'] != 0:
adam_step.add_(p.data, alpha=group['weight_decay'])
adam_norm = adam_step.pow(2).sum().sqrt()
if weight_norm == 0 or adam_norm == 0:
trust_ratio = 1
else:
trust_ratio = weight_norm / adam_norm
state['weight_norm'] = weight_norm
state['adam_norm'] = adam_norm
state['trust_ratio'] = trust_ratio
if self.adam:
trust_ratio = 1
p.data.add_(adam_step, alpha=-step_size * trust_ratio)
return loss
def debug(self):
"""Returns a histogram dict for recording various norms and the trust ratio."""
results = collections.defaultdict(list)
for group in self.param_groups:
for p in group['params']:
state = self.state[p]
for i in ('weight_norm', 'adam_norm', 'trust_ratio'):
if i in state:
results[i].append(state[i])
res = {}
for k, v in results.items():
res[f'histogram_lamb_{k}'] = torch.tensor(v)
return res

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@ -154,6 +154,18 @@ class ConfigurableStep(Module):
weight_decay=opt_config['weight_decay'])
opt = LARC(optSGD, trust_coefficient=opt_config['lars_coefficient'])
opt._group_names = sorted(list(all_param_names))
elif self.step_opt['optimizer'] == 'lamb':
from trainer.optimizers.lamb import Lamb
opt_unweighted = torch.optim.AdamW(params_notweights, lr=opt_config['lr'], weight_decay=0,
betas=(opt_get(opt_config, ['beta1'], .9), opt_get(opt_config, ['beta2'], .999)))
opt_unweighted._config = opt_config
opt_unweighted._config['network'] = net_name
self.optimizers.append(opt_unweighted)
opt = Lamb(params_weights, lr=opt_config['lr'],
weight_decay=opt_get(opt_config, ['weight_decay'], 1e-2),
betas=(opt_get(opt_config, ['beta1'], .9), opt_get(opt_config, ['beta2'], .999)))
opt._group_names = [params_names_weights, params_names_notweights]
elif self.step_opt['optimizer'] == 'sgd':
from torch.optim import SGD
opt = SGD(list(optim_params.values()), lr=opt_config['lr'], momentum=opt_config['momentum'], weight_decay=opt_config['weight_decay'])