Added adafactor implementation that handles stochastic rounding of update and accumulation
This commit is contained in:
Jaret Burkett
305
toolkit/optimizers/adafactor.py
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305
toolkit/optimizers/adafactor.py
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import math
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from typing import List
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import torch
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from toolkit.optimizers.optimizer_utils import copy_stochastic, stochastic_grad_accummulation
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class Adafactor(torch.optim.Optimizer):
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"""
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Adafactor implementation with stochastic rounding accumulation and stochastic rounding on apply.
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Modified from transformers Adafactor implementation to support stochastic rounding accumulation and apply.
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AdaFactor pytorch implementation can be used as a drop in replacement for Adam original fairseq code:
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https://github.com/pytorch/fairseq/blob/master/fairseq/optim/adafactor.py
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Paper: *Adafactor: Adaptive Learning Rates with Sublinear Memory Cost* https://arxiv.org/abs/1804.04235 Note that
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this optimizer internally adjusts the learning rate depending on the `scale_parameter`, `relative_step` and
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`warmup_init` options. To use a manual (external) learning rate schedule you should set `scale_parameter=False` and
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`relative_step=False`.
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Arguments:
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params (`Iterable[nn.parameter.Parameter]`):
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Iterable of parameters to optimize or dictionaries defining parameter groups.
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lr (`float`, *optional*):
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The external learning rate.
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eps (`Tuple[float, float]`, *optional*, defaults to `(1e-30, 0.001)`):
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Regularization constants for square gradient and parameter scale respectively
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clip_threshold (`float`, *optional*, defaults to 1.0):
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Threshold of root mean square of final gradient update
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decay_rate (`float`, *optional*, defaults to -0.8):
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Coefficient used to compute running averages of square
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beta1 (`float`, *optional*):
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Coefficient used for computing running averages of gradient
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weight_decay (`float`, *optional*, defaults to 0.0):
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Weight decay (L2 penalty)
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scale_parameter (`bool`, *optional*, defaults to `True`):
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If True, learning rate is scaled by root mean square
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relative_step (`bool`, *optional*, defaults to `True`):
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If True, time-dependent learning rate is computed instead of external learning rate
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warmup_init (`bool`, *optional*, defaults to `False`):
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Time-dependent learning rate computation depends on whether warm-up initialization is being used
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This implementation handles low-precision (FP16, bfloat) values, but we have not thoroughly tested.
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Recommended T5 finetuning settings (https://discuss.huggingface.co/t/t5-finetuning-tips/684/3):
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- Training without LR warmup or clip_threshold is not recommended.
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- use scheduled LR warm-up to fixed LR
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- use clip_threshold=1.0 (https://arxiv.org/abs/1804.04235)
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- Disable relative updates
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- Use scale_parameter=False
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- Additional optimizer operations like gradient clipping should not be used alongside Adafactor
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Example:
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```python
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Adafactor(model.parameters(), scale_parameter=False, relative_step=False, warmup_init=False, lr=1e-3)
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```
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Others reported the following combination to work well:
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```python
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Adafactor(model.parameters(), scale_parameter=True, relative_step=True, warmup_init=True, lr=None)
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```
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When using `lr=None` with [`Trainer`] you will most likely need to use [`~optimization.AdafactorSchedule`]
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scheduler as following:
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```python
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from transformers.optimization import Adafactor, AdafactorSchedule
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optimizer = Adafactor(model.parameters(), scale_parameter=True, relative_step=True, warmup_init=True, lr=None)
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lr_scheduler = AdafactorSchedule(optimizer)
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trainer = Trainer(..., optimizers=(optimizer, lr_scheduler))
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```
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Usage:
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```python
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# replace AdamW with Adafactor
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optimizer = Adafactor(
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model.parameters(),
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lr=1e-3,
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eps=(1e-30, 1e-3),
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clip_threshold=1.0,
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decay_rate=-0.8,
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beta1=None,
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weight_decay=0.0,
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relative_step=False,
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scale_parameter=False,
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warmup_init=False,
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)
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```"""
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def __init__(
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self,
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params,
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lr=None,
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eps=(1e-30, 1e-3),
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clip_threshold=1.0,
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decay_rate=-0.8,
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beta1=None,
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weight_decay=0.0,
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scale_parameter=True,
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relative_step=True,
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warmup_init=False,
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):
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if lr is not None and relative_step:
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raise ValueError(
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"Cannot combine manual `lr` and `relative_step=True` options")
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if warmup_init and not relative_step:
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raise ValueError(
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"`warmup_init=True` requires `relative_step=True`")
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defaults = {
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"lr": lr,
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"eps": eps,
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"clip_threshold": clip_threshold,
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"decay_rate": decay_rate,
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"beta1": beta1,
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"weight_decay": weight_decay,
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"scale_parameter": scale_parameter,
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"relative_step": relative_step,
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"warmup_init": warmup_init,
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}
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super().__init__(params, defaults)
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self.base_lrs: List[float] = [
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lr for group in self.param_groups
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]
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self.is_stochastic_rounding_accumulation = False
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# setup stochastic grad accum hooks
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for group in self.param_groups:
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for param in group['params']:
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if param.requires_grad and param.dtype != torch.float32:
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self.is_stochastic_rounding_accumulation = True
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param.register_post_accumulate_grad_hook(
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stochastic_grad_accummulation
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)
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@staticmethod
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def _get_lr(param_group, param_state):
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rel_step_sz = param_group["lr"]
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if param_group["relative_step"]:
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min_step = 1e-6 * \
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param_state["step"] if param_group["warmup_init"] else 1e-2
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rel_step_sz = min(min_step, 1.0 / math.sqrt(param_state["step"]))
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param_scale = 1.0
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if param_group["scale_parameter"]:
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param_scale = max(param_group["eps"][1], param_state["RMS"])
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return param_scale * rel_step_sz
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@staticmethod
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def _get_options(param_group, param_shape):
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factored = len(param_shape) >= 2
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use_first_moment = param_group["beta1"] is not None
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return factored, use_first_moment
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@staticmethod
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def _rms(tensor):
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return tensor.norm(2) / (tensor.numel() ** 0.5)
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@staticmethod
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def _approx_sq_grad(exp_avg_sq_row, exp_avg_sq_col):
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# copy from fairseq's adafactor implementation:
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# https://github.com/huggingface/transformers/blob/8395f14de6068012787d83989c3627c3df6a252b/src/transformers/optimization.py#L505
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r_factor = (exp_avg_sq_row / exp_avg_sq_row.mean(dim=-
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1, keepdim=True)).rsqrt_().unsqueeze(-1)
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c_factor = exp_avg_sq_col.unsqueeze(-2).rsqrt()
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return torch.mul(r_factor, c_factor)
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def step_hook(self):
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if not self.is_stochastic_rounding_accumulation:
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return
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# copy over stochastically rounded grads
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for group in self.param_groups:
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for param in group['params']:
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if param.requires_grad and hasattr(param, "_accum_grad"):
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param.grad = param._accum_grad
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del param._accum_grad
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# adafactor manages its own lr
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def get_learning_rates(self):
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lrs = [
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self._get_lr(group, self.state[group["params"][0]])
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for group in self.param_groups
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if group["params"][0].grad is not None
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]
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if len(lrs) == 0:
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lrs = self.base_lrs # if called before stepping
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return lrs
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@torch.no_grad()
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def step(self, closure=None):
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"""
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Performs a single optimization step
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Arguments:
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closure (callable, optional): A closure that reevaluates the model
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and returns the loss.
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"""
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self.step_hook()
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loss = None
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if closure is not None:
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loss = closure()
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for group in self.param_groups:
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for p in group["params"]:
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if p.grad is None:
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continue
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grad = p.grad
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if grad.dtype != torch.float32:
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grad = grad.to(torch.float32)
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if grad.is_sparse:
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raise RuntimeError(
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"Adafactor does not support sparse gradients.")
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state = self.state[p]
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grad_shape = grad.shape
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factored, use_first_moment = self._get_options(
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group, grad_shape)
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# State Initialization
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if len(state) == 0:
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state["step"] = 0
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if use_first_moment:
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# Exponential moving average of gradient values
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state["exp_avg"] = torch.zeros_like(grad)
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if factored:
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state["exp_avg_sq_row"] = torch.zeros(
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grad_shape[:-1]).to(grad)
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state["exp_avg_sq_col"] = torch.zeros(
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grad_shape[:-2] + grad_shape[-1:]).to(grad)
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else:
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state["exp_avg_sq"] = torch.zeros_like(grad)
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state["RMS"] = 0
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else:
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if use_first_moment:
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state["exp_avg"] = state["exp_avg"].to(grad)
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if factored:
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state["exp_avg_sq_row"] = state["exp_avg_sq_row"].to(
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grad)
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state["exp_avg_sq_col"] = state["exp_avg_sq_col"].to(
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grad)
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else:
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state["exp_avg_sq"] = state["exp_avg_sq"].to(grad)
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p_data_fp32 = p
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if p.dtype != torch.float32:
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p_data_fp32 = p_data_fp32.clone().float()
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state["step"] += 1
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state["RMS"] = self._rms(p_data_fp32)
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lr = self._get_lr(group, state)
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beta2t = 1.0 - math.pow(state["step"], group["decay_rate"])
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eps = group["eps"]
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if isinstance(eps, tuple) or isinstance(eps, list):
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eps = eps[0]
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update = (grad**2) + eps
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if factored:
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exp_avg_sq_row = state["exp_avg_sq_row"]
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exp_avg_sq_col = state["exp_avg_sq_col"]
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exp_avg_sq_row.mul_(beta2t).add_(
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update.mean(dim=-1), alpha=(1.0 - beta2t))
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exp_avg_sq_col.mul_(beta2t).add_(
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update.mean(dim=-2), alpha=(1.0 - beta2t))
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# Approximation of exponential moving average of square of gradient
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update = self._approx_sq_grad(
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exp_avg_sq_row, exp_avg_sq_col)
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update.mul_(grad)
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else:
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exp_avg_sq = state["exp_avg_sq"]
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exp_avg_sq.mul_(beta2t).add_(update, alpha=(1.0 - beta2t))
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update = exp_avg_sq.rsqrt().mul_(grad)
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update.div_(
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(self._rms(update) / group["clip_threshold"]).clamp_(min=1.0))
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update.mul_(lr)
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if use_first_moment:
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exp_avg = state["exp_avg"]
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exp_avg.mul_(group["beta1"]).add_(
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update, alpha=(1 - group["beta1"]))
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update = exp_avg
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if group["weight_decay"] != 0:
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p_data_fp32.add_(
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p_data_fp32, alpha=(-group["weight_decay"] * lr))
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p_data_fp32.add_(-update)
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if p.dtype != torch.float32:
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# apply stochastic rounding
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copy_stochastic(p, p_data_fp32)
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return loss
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