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Overview

8-bit optimizers reduce the memory footprint of 32-bit optimizers without any performance degradation which means you can train large models with many parameters faster. At the core of 8-bit optimizers is block-wise quantization which enables quantization accuracy, computational efficiency, and stability.

bitsandbytes provides 8-bit optimizers through the base Optimizer8bit class, and additionally provides Optimizer2State and Optimizer1State for 2-state (for example, Adam) and 1-state (for example, Adagrad) optimizers respectively. To provide custom optimizer hyperparameters, use the GlobalOptimManager class to configure the optimizer.

Optimizer8bit

class bitsandbytes.optim.optimizer.Optimizer8bit

< >

( params defaults optim_bits = 32 is_paged = False )

__init__

< >

( params defaults optim_bits = 32 is_paged = False )

Parameters

  • params (torch.tensor) — The input parameters to optimize.
  • optim_bits (int, defaults to 32) — The number of bits of the optimizer state.
  • is_paged (bool, defaults to False) — Whether the optimizer is a paged optimizer or not.

Base 8-bit optimizer class.

Optimizer2State

class bitsandbytes.optim.optimizer.Optimizer2State

< >

( optimizer_name params lr = 0.001 betas = (0.9, 0.999) eps = 1e-08 weight_decay = 0.0 optim_bits = 32 args = None min_8bit_size = 4096 percentile_clipping = 100 block_wise = True max_unorm = 0.0 skip_zeros = False is_paged = False )

__init__

< >

( optimizer_name params lr = 0.001 betas = (0.9, 0.999) eps = 1e-08 weight_decay = 0.0 optim_bits = 32 args = None min_8bit_size = 4096 percentile_clipping = 100 block_wise = True max_unorm = 0.0 skip_zeros = False is_paged = False )

Parameters

  • optimizer_name (str) — The name of the optimizer.
  • params (torch.tensor) — The input parameters to optimize.
  • lr (float, defaults to 1e-3) — The learning rate.
  • betas (tuple, defaults to (0.9, 0.999)) — The beta values for the optimizer.
  • eps (float, defaults to 1e-8) — The epsilon value for the optimizer.
  • weight_decay (float, defaults to 0.0) — The weight decay value for the optimizer.
  • optim_bits (int, defaults to 32) — The number of bits of the optimizer state.
  • args (object, defaults to None) — An object with additional arguments.
  • min_8bit_size (int, defaults to 4096) — The minimum number of elements of the parameter tensors for 8-bit optimization.
  • percentile_clipping (int, defaults to 100) — Adapts clipping threshold automatically by tracking the last 100 gradient norms and clipping the gradient at a certain percentile to improve stability.
  • block_wise (bool, defaults to True) — Whether to independently quantize each block of tensors to reduce outlier effects and improve stability.
  • max_unorm (float, defaults to 0.0) — The maximum value to normalize each block with.
  • skip_zeros (bool, defaults to False) — Whether to skip zero values for sparse gradients and models to ensure correct updates.
  • is_paged (bool, defaults to False) — Whether the optimizer is a paged optimizer or not.

Base 2-state update optimizer class.

Optimizer1State

class bitsandbytes.optim.optimizer.Optimizer1State

< >

( optimizer_name params lr = 0.001 betas = (0.9, 0.0) eps = 1e-08 weight_decay = 0.0 optim_bits = 32 args = None min_8bit_size = 4096 percentile_clipping = 100 block_wise = True max_unorm = 0.0 skip_zeros = False is_paged = False )

__init__

< >

( optimizer_name params lr = 0.001 betas = (0.9, 0.0) eps = 1e-08 weight_decay = 0.0 optim_bits = 32 args = None min_8bit_size = 4096 percentile_clipping = 100 block_wise = True max_unorm = 0.0 skip_zeros = False is_paged = False )

Parameters

  • optimizer_name (str) — The name of the optimizer.
  • params (torch.tensor) — The input parameters to optimize.
  • lr (float, defaults to 1e-3) — The learning rate.
  • betas (tuple, defaults to (0.9, 0.0)) — The beta values for the optimizer.
  • eps (float, defaults to 1e-8) — The epsilon value for the optimizer.
  • weight_decay (float, defaults to 0.0) — The weight decay value for the optimizer.
  • optim_bits (int, defaults to 32) — The number of bits of the optimizer state.
  • args (object, defaults to None) — An object with additional arguments.
  • min_8bit_size (int, defaults to 4096) — The minimum number of elements of the parameter tensors for 8-bit optimization.
  • percentile_clipping (int, defaults to 100) — Adapts clipping threshold automatically by tracking the last 100 gradient norms and clipping the gradient at a certain percentile to improve stability.
  • block_wise (bool, defaults to True) — Whether to independently quantize each block of tensors to reduce outlier effects and improve stability.
  • max_unorm (float, defaults to 0.0) — The maximum value to normalize each block with.
  • skip_zeros (bool, defaults to False) — Whether to skip zero values for sparse gradients and models to ensure correct updates.
  • is_paged (bool, defaults to False) — Whether the optimizer is a paged optimizer or not.

Base 1-state update optimizer class.

Utilities

class bitsandbytes.optim.GlobalOptimManager

< >

( )

A global optimizer manager for enabling custom optimizer configs.

override_config

< >

( parameters key = None value = None key_value_dict = None )

Parameters

  • parameters (torch.Tensor or list(torch.Tensors)) — The input parameters.
  • key (str) — The hyperparamter to override. value — The hyperparameter values.
  • key_value_dict (dict) — A dictionary with multiple key-values to override.

Override initial optimizer config with specific hyperparameters.

The key-values of the optimizer config for the input parameters are overridden This can be both, optimizer parameters like betas or lr, or it can be 8-bit specific parameters like optim_bits or percentile_clipping.

Example:

import torch
import bitsandbytes as bnb

mng = bnb.optim.GlobalOptimManager.get_instance()

model = MyModel()
mng.register_parameters(model.parameters()) # 1. register parameters while still on CPU

model = model.cuda()
# use 8-bit optimizer states for all parameters
adam = bnb.optim.Adam(model.parameters(), lr=0.001, optim_bits=8)

# 2. override: the parameter model.fc1.weight now uses 32-bit Adam
mng.override_config(model.fc1.weight, 'optim_bits', 32)
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