param_init_fns.py

import math
import warnings
from collections.abc import Sequence
from functools import partial
from typing import Optional, Tuple, Union
import torch
from torch import nn
from .fc import FC_CLASS_REGISTRY
from .norm import NORM_CLASS_REGISTRY
try:
    import transformer_engine.pytorch as te
except:
    te = None

def torch_default_param_init_fn_(module: nn.Module, verbose: int=0, **kwargs):
    del kwargs
    if verbose > 1:
        warnings.warn(f"Initializing network using module's reset_parameters attribute")
    if hasattr(module, 'reset_parameters'):
        module.reset_parameters()

def fused_init_helper_(module: nn.Module, init_fn_):
    _fused = getattr(module, '_fused', None)
    if _fused is None:
        raise RuntimeError(f'Internal logic error')
    (dim, splits) = _fused
    splits = (0, *splits, module.weight.size(dim))
    for (s, e) in zip(splits[:-1], splits[1:]):
        slice_indices = [slice(None)] * module.weight.ndim
        slice_indices[dim] = slice(s, e)
        init_fn_(module.weight[slice_indices])

def generic_param_init_fn_(module: nn.Module, init_fn_, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, verbose: int=0, **kwargs):
    del kwargs
    if verbose > 1:
        warnings.warn(f'If model has bias parameters they are initialized to 0.')
    init_div_is_residual = init_div_is_residual
    if init_div_is_residual is False:
        div_is_residual = 1.0
    elif init_div_is_residual is True:
        div_is_residual = math.sqrt(2 * n_layers)
    elif isinstance(init_div_is_residual, float) or isinstance(init_div_is_residual, int):
        div_is_residual = init_div_is_residual
    elif isinstance(init_div_is_residual, str) and init_div_is_residual.isnumeric():
        div_is_residual = float(init_div_is_residual)
    else:
        div_is_residual = 1.0
        raise ValueError(f'Expected init_div_is_residual to be boolean or numeric, got {init_div_is_residual}')
    if init_div_is_residual is not False:
        if verbose > 1:
            warnings.warn(f'Initializing _is_residual layers then dividing them by {div_is_residual:.3f}. ' + f'Set `init_div_is_residual: false` in init config to disable this.')
    if isinstance(module, tuple(set(FC_CLASS_REGISTRY.values()))):
        if hasattr(module, '_fused'):
            fused_init_helper_(module, init_fn_)
        else:
            init_fn_(module.weight)
        if module.bias is not None:
            torch.nn.init.zeros_(module.bias)
        if init_div_is_residual is not False and getattr(module, '_is_residual', False):
            with torch.no_grad():
                module.weight.div_(div_is_residual)
    elif isinstance(module, nn.Embedding):
        if emb_init_std is not None:
            std = emb_init_std
            if std == 0:
                warnings.warn(f'Embedding layer initialized to 0.')
            emb_init_fn_ = partial(torch.nn.init.normal_, mean=0.0, std=std)
            if verbose > 1:
                warnings.warn(f'Embedding layer initialized using normal distribution with mean=0 and std={std!r}.')
        elif emb_init_uniform_lim is not None:
            lim = emb_init_uniform_lim
            if isinstance(lim, Sequence):
                if len(lim) > 2:
                    raise ValueError(f'Uniform init requires a min and a max limit. User input: {lim}.')
                if lim[0] == lim[1]:
                    warnings.warn(f'Embedding layer initialized to {lim[0]}.')
            else:
                if lim == 0:
                    warnings.warn(f'Embedding layer initialized to 0.')
                lim = [-lim, lim]
            (a, b) = lim
            emb_init_fn_ = partial(torch.nn.init.uniform_, a=a, b=b)
            if verbose > 1:
                warnings.warn(f'Embedding layer initialized using uniform distribution in range {lim}.')
        else:
            emb_init_fn_ = init_fn_
        emb_init_fn_(module.weight)
    elif isinstance(module, tuple(set(NORM_CLASS_REGISTRY.values()))):
        if verbose > 1:
            warnings.warn(f'Norm weights are set to 1. If norm layer has a bias it is initialized to 0.')
        if hasattr(module, 'weight') and module.weight is not None:
            torch.nn.init.ones_(module.weight)
        if hasattr(module, 'bias') and module.bias is not None:
            torch.nn.init.zeros_(module.bias)
    elif isinstance(module, nn.MultiheadAttention):
        if module._qkv_same_embed_dim:
            assert module.in_proj_weight is not None
            assert module.q_proj_weight is None and module.k_proj_weight is None and (module.v_proj_weight is None)
            assert d_model is not None
            _d = d_model
            splits = (0, _d, 2 * _d, 3 * _d)
            for (s, e) in zip(splits[:-1], splits[1:]):
                init_fn_(module.in_proj_weight[s:e])
        else:
            assert module.q_proj_weight is not None and module.k_proj_weight is not None and (module.v_proj_weight is not None)
            assert module.in_proj_weight is None
            init_fn_(module.q_proj_weight)
            init_fn_(module.k_proj_weight)
            init_fn_(module.v_proj_weight)
        if module.in_proj_bias is not None:
            torch.nn.init.zeros_(module.in_proj_bias)
        if module.bias_k is not None:
            torch.nn.init.zeros_(module.bias_k)
        if module.bias_v is not None:
            torch.nn.init.zeros_(module.bias_v)
        init_fn_(module.out_proj.weight)
        if init_div_is_residual is not False and getattr(module.out_proj, '_is_residual', False):
            with torch.no_grad():
                module.out_proj.weight.div_(div_is_residual)
        if module.out_proj.bias is not None:
            torch.nn.init.zeros_(module.out_proj.bias)
    elif te is not None and isinstance(module, te.LayerNormMLP):
        if module.layer_norm_weight is not None:
            torch.nn.init.ones_(module.layer_norm_weight)
        if module.layer_norm_bias is not None:
            torch.nn.init.zeros_(module.layer_norm_bias)
        init_fn_(module.fc1_weight)
        if module.fc1_bias is not None:
            torch.nn.init.zeros_(module.fc1_bias)
        init_fn_(module.fc2_weight)
        if module.fc2_bias is not None:
            torch.nn.init.zeros_(module.fc2_bias)
        with torch.no_grad():
            module.fc2_weight.div_(div_is_residual)
    else:
        for _ in module.parameters(recurse=False):
            raise NotImplementedError(f'{module.__class__.__name__} parameters are not initialized by param_init_fn.')

def _normal_init_(std, mean=0.0):
    return partial(torch.nn.init.normal_, mean=mean, std=std)

def _normal_param_init_fn_(module: nn.Module, std: float, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, verbose: int=0, **kwargs):
    del kwargs
    init_fn_ = _normal_init_(std=std)
    if verbose > 1:
        warnings.warn(f'Using torch.nn.init.normal_ init fn mean=0.0, std={std}')
    generic_param_init_fn_(module=module, init_fn_=init_fn_, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def baseline_param_init_fn_(module: nn.Module, init_std: float, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, verbose: int=0, **kwargs):
    del kwargs
    if init_std is None:
        raise ValueError("You must set model.init_config['init_std'] to a float value to use the default initialization scheme.")
    _normal_param_init_fn_(module=module, std=init_std, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def small_param_init_fn_(module: nn.Module, n_layers: int, d_model: int, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, verbose: int=0, **kwargs):
    del kwargs
    std = math.sqrt(2 / (5 * d_model))
    _normal_param_init_fn_(module=module, std=std, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def neox_param_init_fn_(module: nn.Module, n_layers: int, d_model: int, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, verbose: int=0, **kwargs):
    """From section 2.3.1 of GPT-NeoX-20B:

    An Open-Source AutoregressiveLanguage Model — Black et. al. (2022)
    see https://github.com/EleutherAI/gpt-neox/blob/9610391ab319403cef079b438edd016a2443af54/megatron/model/init_functions.py#L151
    and https://github.com/EleutherAI/gpt-neox/blob/main/megatron/model/transformer.py
    """
    del kwargs
    residual_div = n_layers / math.sqrt(10)
    if verbose > 1:
        warnings.warn(f'setting init_div_is_residual to {residual_div}')
    small_param_init_fn_(module=module, d_model=d_model, n_layers=n_layers, init_div_is_residual=residual_div, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def kaiming_uniform_param_init_fn_(module: nn.Module, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, init_gain: float=0, fan_mode: str='fan_in', init_nonlinearity: str='leaky_relu', verbose: int=0, **kwargs):
    del kwargs
    if verbose > 1:
        warnings.warn(f'Using nn.init.kaiming_uniform_ init fn with parameters: ' + f'a={init_gain}, mode={fan_mode}, nonlinearity={init_nonlinearity}')
    kaiming_uniform_ = partial(nn.init.kaiming_uniform_, a=init_gain, mode=fan_mode, nonlinearity=init_nonlinearity)
    generic_param_init_fn_(module=module, init_fn_=kaiming_uniform_, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def kaiming_normal_param_init_fn_(module: nn.Module, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, init_gain: float=0, fan_mode: str='fan_in', init_nonlinearity: str='leaky_relu', verbose: int=0, **kwargs):
    del kwargs
    if verbose > 1:
        warnings.warn(f'Using nn.init.kaiming_normal_ init fn with parameters: ' + f'a={init_gain}, mode={fan_mode}, nonlinearity={init_nonlinearity}')
    kaiming_normal_ = partial(torch.nn.init.kaiming_normal_, a=init_gain, mode=fan_mode, nonlinearity=init_nonlinearity)
    generic_param_init_fn_(module=module, init_fn_=kaiming_normal_, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def xavier_uniform_param_init_fn_(module: nn.Module, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, init_gain: float=0, verbose: int=0, **kwargs):
    del kwargs
    xavier_uniform_ = partial(torch.nn.init.xavier_uniform_, gain=init_gain)
    if verbose > 1:
        warnings.warn(f'Using torch.nn.init.xavier_uniform_ init fn with parameters: ' + f'gain={init_gain}')
    generic_param_init_fn_(module=module, init_fn_=xavier_uniform_, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)

def xavier_normal_param_init_fn_(module: nn.Module, n_layers: int, d_model: Optional[int]=None, init_div_is_residual: Union[int, float, str, bool]=True, emb_init_std: Optional[float]=None, emb_init_uniform_lim: Optional[Union[Tuple[float, float], float]]=None, init_gain: float=0, verbose: int=0, **kwargs):
    xavier_normal_ = partial(torch.nn.init.xavier_normal_, gain=init_gain)
    if verbose > 1:
        warnings.warn(f'Using torch.nn.init.xavier_normal_ init fn with parameters: ' + f'gain={init_gain}')
    generic_param_init_fn_(module=module, init_fn_=xavier_normal_, d_model=d_model, n_layers=n_layers, init_div_is_residual=init_div_is_residual, emb_init_std=emb_init_std, emb_init_uniform_lim=emb_init_uniform_lim, verbose=verbose)
MODEL_INIT_REGISTRY = {'default_': torch_default_param_init_fn_, 'baseline_': baseline_param_init_fn_, 'kaiming_uniform_': kaiming_uniform_param_init_fn_, 'kaiming_normal_': kaiming_normal_param_init_fn_, 'neox_init_': neox_param_init_fn_, 'small_init_': small_param_init_fn_, 'xavier_uniform_': xavier_uniform_param_init_fn_, 'xavier_normal_': xavier_normal_param_init_fn_}