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Source code for mmcls.core.optimizers.lamb

"""PyTorch Lamb optimizer w/ behaviour similar to NVIDIA FusedLamb.

This optimizer code was adapted from the following (starting with latest)
* https://github.com/HabanaAI/Model-References/blob/
2b435114fe8e31f159b1d3063b8280ae37af7423/PyTorch/nlp/bert/pretraining/lamb.py
* https://github.com/NVIDIA/DeepLearningExamples/blob/master/PyTorch/
LanguageModeling/Transformer-XL/pytorch/lamb.py
* https://github.com/cybertronai/pytorch-lamb

Use FusedLamb if you can (GPU). The reason for including this variant of Lamb
is to have a version that is
similar in behaviour to APEX FusedLamb if you aren't using NVIDIA GPUs or
cannot install/use APEX.

In addition to some cleanup, this Lamb impl has been modified to support
PyTorch XLA and has been tested on TPU.

Original copyrights for above sources are below.

Modifications Copyright 2021 Ross Wightman
"""
# Copyright (c) 2021, Habana Labs Ltd.  All rights reserved.

# Copyright (c) 2019-2020, NVIDIA CORPORATION. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# MIT License
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# Copyright (c) 2019 cybertronai
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# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
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# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
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# SOFTWARE.
import math

import torch
from mmcv.runner import OPTIMIZERS
from torch.optim import Optimizer


[docs]@OPTIMIZERS.register_module() class Lamb(Optimizer): """A pure pytorch variant of FuseLAMB (NvLamb variant) optimizer. This class is copied from `timm`_. The LAMB was proposed in `Large Batch Optimization for Deep Learning - Training BERT in 76 minutes`_. .. _timm: https://github.com/rwightman/pytorch-image-models/blob/master/timm/optim/lamb.py .. _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) betas (Tuple[float, float], optional): coefficients used for computing running averages of gradient and its norm. (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) grad_averaging (bool, optional): whether apply (1-beta2) to grad when calculating running averages of gradient. (default: True) max_grad_norm (float, optional): value used to clip global grad norm (default: 1.0) trust_clip (bool): enable LAMBC trust ratio clipping (default: False) always_adapt (boolean, optional): Apply adaptive learning rate to 0.0 weight decay parameter (default: False) """ # noqa: E501 def __init__(self, params, lr=1e-3, bias_correction=True, betas=(0.9, 0.999), eps=1e-6, weight_decay=0.01, grad_averaging=True, max_grad_norm=1.0, trust_clip=False, always_adapt=False): defaults = dict( lr=lr, bias_correction=bias_correction, betas=betas, eps=eps, weight_decay=weight_decay, grad_averaging=grad_averaging, max_grad_norm=max_grad_norm, trust_clip=trust_clip, always_adapt=always_adapt) super().__init__(params, defaults)
[docs] @torch.no_grad() 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: with torch.enable_grad(): loss = closure() device = self.param_groups[0]['params'][0].device one_tensor = torch.tensor( 1.0, device=device ) # because torch.where doesn't handle scalars correctly global_grad_norm = torch.zeros(1, device=device) for group in self.param_groups: for p in group['params']: if p.grad is None: continue grad = p.grad if grad.is_sparse: raise RuntimeError( 'Lamb does not support sparse gradients, consider ' 'SparseAdam instead.') global_grad_norm.add_(grad.pow(2).sum()) global_grad_norm = torch.sqrt(global_grad_norm) # FIXME it'd be nice to remove explicit tensor conversion of scalars # when torch.where promotes # scalar types properly https://github.com/pytorch/pytorch/issues/9190 max_grad_norm = torch.tensor( self.defaults['max_grad_norm'], device=device) clip_global_grad_norm = torch.where(global_grad_norm > max_grad_norm, global_grad_norm / max_grad_norm, one_tensor) for group in self.param_groups: bias_correction = 1 if group['bias_correction'] else 0 beta1, beta2 = group['betas'] grad_averaging = 1 if group['grad_averaging'] else 0 beta3 = 1 - beta1 if grad_averaging else 1.0 # assume same step across group now to simplify things # per parameter step can be easily support by making it tensor, or # pass list into kernel if 'step' in group: group['step'] += 1 else: group['step'] = 1 if bias_correction: bias_correction1 = 1 - beta1**group['step'] bias_correction2 = 1 - beta2**group['step'] else: bias_correction1, bias_correction2 = 1.0, 1.0 for p in group['params']: if p.grad is None: continue grad = p.grad.div_(clip_global_grad_norm) state = self.state[p] # State initialization if len(state) == 0: # Exponential moving average of gradient valuesa state['exp_avg'] = torch.zeros_like(p) # Exponential moving average of squared gradient values state['exp_avg_sq'] = torch.zeros_like(p) exp_avg, exp_avg_sq = state['exp_avg'], state['exp_avg_sq'] # Decay the first and second moment running average coefficient exp_avg.mul_(beta1).add_(grad, alpha=beta3) # m_t exp_avg_sq.mul_(beta2).addcmul_( grad, grad, value=1 - beta2) # v_t denom = (exp_avg_sq.sqrt() / math.sqrt(bias_correction2)).add_( group['eps']) update = (exp_avg / bias_correction1).div_(denom) weight_decay = group['weight_decay'] if weight_decay != 0: update.add_(p, alpha=weight_decay) if weight_decay != 0 or group['always_adapt']: # Layer-wise LR adaptation. By default, skip adaptation on # parameters that are # excluded from weight decay, unless always_adapt == True, # then always enabled. w_norm = p.norm(2.0) g_norm = update.norm(2.0) # FIXME nested where required since logical and/or not # working in PT XLA trust_ratio = torch.where( w_norm > 0, torch.where(g_norm > 0, w_norm / g_norm, one_tensor), one_tensor, ) if group['trust_clip']: # LAMBC trust clipping, upper bound fixed at one trust_ratio = torch.minimum(trust_ratio, one_tensor) update.mul_(trust_ratio) p.add_(update, alpha=-group['lr']) return loss
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