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Source code for torch.ao.quantization.fake_quantize

"""
This module implements modules which are used to perform fake quantization
during QAT.
"""

import torch
from torch.nn import Module
from torch.ao.quantization.observer import (
    MovingAverageMinMaxObserver,
    HistogramObserver,
    MovingAveragePerChannelMinMaxObserver,
    PerChannelMinMaxObserver,
    _with_args,
)
import re
from abc import ABC, abstractmethod
from typing import Any, Tuple

def _is_per_channel(qscheme: 'torch.qscheme') -> bool:
    return qscheme in [torch.per_channel_symmetric, torch.per_channel_affine, torch.per_channel_affine_float_qparams]

def _is_per_tensor(qscheme: 'torch.qscheme') -> bool:
    return qscheme in [torch.per_tensor_symmetric, torch.per_tensor_affine]

def _is_symmetric_quant(qscheme: 'torch.qscheme') -> bool:
    return qscheme in [torch.per_tensor_symmetric, torch.per_channel_symmetric]

[docs]class FakeQuantizeBase(ABC, Module): r""" Base fake quantize module Any fake quantize implementation should derive from this class. Concrete fake quantize module should follow the same API. In forward, they will update the statistics of the observed Tensor and fake quantize the input. They should also provide a `calculate_qparams` function that computes the quantization parameters given the collected statistics. """ fake_quant_enabled: torch.Tensor observer_enabled: torch.Tensor def __init__(self): super().__init__() # fake_quant_enabled and observer_enabled are buffers to support their # replication in DDP. Data type is uint8 because NCCL does not support # bool tensors. self.register_buffer('fake_quant_enabled', torch.tensor([1], dtype=torch.uint8)) self.register_buffer('observer_enabled', torch.tensor([1], dtype=torch.uint8)) @abstractmethod def forward(self, x): pass @abstractmethod def calculate_qparams(self, **kwargs): pass @torch.jit.export def enable_fake_quant(self, enabled: bool = True) -> None: self.fake_quant_enabled[0] = 1 if enabled else 0 @torch.jit.export def disable_fake_quant(self): self.enable_fake_quant(False) @torch.jit.export def enable_observer(self, enabled: bool = True) -> None: self.observer_enabled[0] = 1 if enabled else 0 @torch.jit.export def disable_observer(self): self.enable_observer(False) with_args = classmethod(_with_args)
[docs]class FakeQuantize(FakeQuantizeBase): r""" Simulate the quantize and dequantize operations in training time. The output of this module is given by:: x_out = ( clamp(round(x/scale + zero_point), quant_min, quant_max) - zero_point ) * scale * :attr:`scale` defines the scale factor used for quantization. * :attr:`zero_point` specifies the quantized value to which 0 in floating point maps to * :attr:`quant_min` specifies the minimum allowable quantized value. * :attr:`quant_max` specifies the maximum allowable quantized value. * :attr:`fake_quant_enabled` controls the application of fake quantization on tensors, note that statistics can still be updated. * :attr:`observer_enabled` controls statistics collection on tensors * :attr:`dtype` specifies the quantized dtype that is being emulated with fake-quantization, allowable values are torch.qint8 and torch.quint8. The values of quant_min and quant_max should be chosen to be consistent with the dtype Args: observer (module): Module for observing statistics on input tensors and calculating scale and zero-point. quant_min (int): The minimum allowable quantized value. quant_max (int): The maximum allowable quantized value. observer_kwargs (optional): Arguments for the observer module Attributes: observer (Module): User provided module that collects statistics on the input tensor and provides a method to calculate scale and zero-point. """ scale: torch.Tensor zero_point: torch.Tensor def __init__(self, observer=MovingAverageMinMaxObserver, quant_min=0, quant_max=255, **observer_kwargs): super().__init__() assert quant_min <= quant_max, \ 'quant_min must be less than or equal to quant_max' self.quant_min = quant_min self.quant_max = quant_max self.activation_post_process = observer(**observer_kwargs) assert torch.iinfo(self.activation_post_process.dtype).min <= quant_min, 'quant_min out of bound' assert quant_max <= torch.iinfo(self.activation_post_process.dtype).max, 'quant_max out of bound' self.register_buffer('scale', torch.tensor([1.0], dtype=torch.float)) self.register_buffer('zero_point', torch.tensor([0], dtype=torch.int)) self.dtype = self.activation_post_process.dtype self.qscheme = self.activation_post_process.qscheme self.ch_axis = self.activation_post_process.ch_axis \ if hasattr(self.activation_post_process, 'ch_axis') else -1 assert _is_per_channel(self.qscheme) or \ _is_per_tensor(self.qscheme), \ 'Only per channel and per tensor quantization are supported in fake quantize' + \ ' got qscheme: ' + str(self.qscheme) self.is_per_channel = _is_per_channel(self.qscheme) @torch.jit.export def calculate_qparams(self): return self.activation_post_process.calculate_qparams() def forward(self, X): if self.observer_enabled[0] == 1: self.activation_post_process(X.detach()) _scale, _zero_point = self.calculate_qparams() _scale, _zero_point = _scale.to(self.scale.device), _zero_point.to(self.zero_point.device) if self.scale.shape != _scale.shape: self.scale.resize_(_scale.shape) self.zero_point.resize_(_zero_point.shape) self.scale.copy_(_scale) self.zero_point.copy_(_zero_point) if self.fake_quant_enabled[0] == 1: if self.is_per_channel: X = torch.fake_quantize_per_channel_affine( X, self.scale, self.zero_point, self.ch_axis, self.quant_min, self.quant_max) else: X = torch.fake_quantize_per_tensor_affine( X, self.scale, self.zero_point, self.quant_min, self.quant_max) return X @torch.jit.export def extra_repr(self): return 'fake_quant_enabled={}, observer_enabled={}, ' \ 'quant_min={}, quant_max={}, dtype={}, qscheme={}, ch_axis={}, ' \ 'scale={}, zero_point={}'.format( self.fake_quant_enabled, self.observer_enabled, self.quant_min, self.quant_max, self.dtype, self.qscheme, self.ch_axis, self.scale, self.zero_point) def _save_to_state_dict(self, destination, prefix, keep_vars): # We cannot currently register scalar values as buffers, so need to manually # specify serialization here. super(FakeQuantize, self)._save_to_state_dict(destination, prefix, keep_vars) destination[prefix + 'scale'] = self.scale destination[prefix + 'zero_point'] = self.zero_point def _load_from_state_dict(self, state_dict, prefix, local_metadata, strict, missing_keys, unexpected_keys, error_msgs): # Removing this function throws an error that the the size of the loaded tensor does not match the original size # i.e., These buffers start out with numel 0 and become numel 1 once they have their first forward pass. local_state = ['scale', 'zero_point'] for name in local_state: key = prefix + name if key in state_dict: val = state_dict[key] # Custom handling to allow loading scale and zero_point # of size N into uninitialized buffers of size 0. The # buffers are resized here, and the values are copied in # the default state_dict loading code of the parent. if name == 'scale': self.scale.resize_(val.shape) else: assert name == 'zero_point' self.zero_point.resize_(val.shape) # For torchscript module we need to update the attributes here since we do not # call the `_load_from_state_dict` function defined module.py if torch.jit.is_scripting(): if name == 'scale': self.scale.copy_(val) else: assert name == 'zero_point' self.zero_point.copy_(val) elif strict: missing_keys.append(key) super(FakeQuantize, self)._load_from_state_dict(state_dict, prefix, local_metadata, strict, missing_keys, unexpected_keys, error_msgs)
[docs]class FixedQParamsFakeQuantize(FakeQuantizeBase): """ Simulate quantize and dequantize with fixed quantization parameters in training time. Only per tensor quantization is supported. Args: `scale` (float): fixed scale for the fake quantize module `zero_point` (int): fixed zero point for the fake quantize module `dtype`, `qscheme`, `quant_min`, `quant_max` """ scale: torch.Tensor zero_point: torch.Tensor def __init__(self, scale, zero_point, dtype=torch.quint8, qscheme=torch.per_tensor_affine, quant_min=0, quant_max=255): super().__init__() assert quant_min <= quant_max, 'quant_min should be less than or equal to quant_max' self.quant_min = quant_min self.quant_max = quant_max self.register_buffer('scale', torch.tensor([scale], dtype=torch.float)) self.register_buffer('zero_point', torch.tensor([zero_point], dtype=torch.int)) self.dtype = dtype self.qscheme = qscheme assert _is_per_tensor(self.qscheme), 'Only per tensor quantization is supported' + \ ' FixedQParamsFakeQuantize module, got qscheme:' + str(self.qscheme) def forward(self, X): if self.fake_quant_enabled[0] == 1: X = torch.fake_quantize_per_tensor_affine(X, self.scale, self.zero_point, self.quant_min, self.quant_max) return X @torch.jit.export def calculate_qparams(self): return self.scale, self.zero_point @torch.jit.export def extra_repr(self): return 'fake_quant_enabled={}, observer_enabled={}, scale={}, zero_point={}, ' \ 'dtype={}, quant_min={}, quant_max={}, qscheme={}'.format( self.fake_quant_enabled, self.observer_enabled, self.scale, self.zero_point, self.dtype, self.quant_min, self.quant_max, self.qscheme)
[docs]class FusedMovingAvgObsFakeQuantize(FakeQuantize): r"""Fused module that is used to observe the input tensor (compute min/max), compute scale/zero_point and fake_quantize the tensor. This module uses calculation similar MovingAverageMinMaxObserver for the inputs, to compute the min/max values in order to compute the scale/zero_point. The qscheme input in the observer is used to differentiate between symmetric/affine quantization scheme. The output of this module is given by x_out = (clamp(round(x/scale + zero_point), quant_min, quant_max)-zero_point)*scale Similar to :class:`~torch.ao.quantization.FakeQuantize`, and accepts the same attributes as the base class. """ def __init__( self, observer: Any = MovingAverageMinMaxObserver, quant_min: int = 0, quant_max: int = 255, **observer_kwargs: Any ) -> None: super().__init__(observer, quant_min, quant_max, **observer_kwargs) assert isinstance(self.activation_post_process, (MovingAverageMinMaxObserver, MovingAveragePerChannelMinMaxObserver)),\ "Fused observer+fake_quant module only works with MovingAverageMinMaxObserver" self.quant_min: int = quant_min self.quant_max: int = quant_max self.register_buffer("fake_quant_enabled", torch.tensor([1], dtype=torch.long)) self.register_buffer("observer_enabled", torch.tensor([1], dtype=torch.long)) self.is_symmetric_quant = _is_symmetric_quant(self.activation_post_process.qscheme) self.quant_min, self.quant_max = self.activation_post_process.quant_min, self.activation_post_process.quant_max @torch.jit.export def calculate_qparams(self) -> Tuple[torch.Tensor, torch.Tensor]: return self.activation_post_process.calculate_qparams() @torch.jit.export def extra_repr(self) -> str: return ( "fake_quant_enabled={}, observer_enabled={}, scale={}, zero_point={}, " "dtype={}, quant_min={}, quant_max={}, qscheme={}, reduce_range={}".format( self.fake_quant_enabled, self.observer_enabled, self.scale, self.zero_point, self.dtype, self.quant_min, self.quant_max, self.qscheme, self.activation_post_process.reduce_range, ) ) def forward(self, X: torch.Tensor) -> torch.Tensor: return torch.fused_moving_avg_obs_fake_quant( X, self.observer_enabled, self.fake_quant_enabled, self.activation_post_process.min_val, self.activation_post_process.max_val, self.scale, self.zero_point, self.activation_post_process.averaging_constant, self.quant_min, self.quant_max, self.ch_axis, self.is_per_channel, self.is_symmetric_quant, )
default_fake_quant = FakeQuantize.with_args(observer=MovingAverageMinMaxObserver, quant_min=0, quant_max=255, dtype=torch.quint8, qscheme=torch.per_tensor_affine, reduce_range=True) """ Default fake_quant for activations. """ default_weight_fake_quant = FakeQuantize.with_args(observer=MovingAverageMinMaxObserver, quant_min=-128, quant_max=127, dtype=torch.qint8, qscheme=torch.per_tensor_symmetric, reduce_range=False) """ Default fake_quant for weights. """ # TODO(future PR): remove these defaults and enforce activation functions # to explicitly specify their output range default_symmetric_fixed_qparams_fake_quant = FixedQParamsFakeQuantize.with_args( scale=2.0 / 256.0, zero_point=128, dtype=torch.quint8, quant_min=0, quant_max=255) default_affine_fixed_qparams_fake_quant = FixedQParamsFakeQuantize.with_args( scale=1.0 / 256.0, zero_point=0, dtype=torch.quint8, quant_min=0, quant_max=255) default_per_channel_weight_fake_quant = FakeQuantize.with_args(observer=MovingAveragePerChannelMinMaxObserver, quant_min=-128, quant_max=127, dtype=torch.qint8, qscheme=torch.per_channel_symmetric, reduce_range=False, ch_axis=0) """ Default fake_quant for per-channel weights. """ default_embedding_fake_quant = FakeQuantize.with_args(observer=PerChannelMinMaxObserver, qscheme=torch.per_channel_affine_float_qparams, ch_axis=0, memoryless=True) """ Default fake_quant for embeddings. """ default_histogram_fake_quant = FakeQuantize.with_args(observer=HistogramObserver, quant_min=0, quant_max=255, dtype=torch.quint8, qscheme=torch.per_tensor_affine, reduce_range=True) """ Fake_quant for activations using a histogram.. """ default_fused_act_fake_quant = FusedMovingAvgObsFakeQuantize.with_args(observer=MovingAverageMinMaxObserver, quant_min=0, quant_max=255, dtype=torch.quint8,) """ Fused version of `default_fake_quant`, with improved performance. """ default_fused_wt_fake_quant = FusedMovingAvgObsFakeQuantize.with_args(observer=MovingAverageMinMaxObserver, quant_min=-128, quant_max=127, dtype=torch.qint8, qscheme=torch.per_tensor_symmetric) """ Fused version of `default_weight_fake_quant`, with improved performance. """ default_fused_per_channel_wt_fake_quant = FusedMovingAvgObsFakeQuantize.with_args(observer=MovingAveragePerChannelMinMaxObserver, quant_min=-128, quant_max=127, dtype=torch.qint8, qscheme=torch.per_channel_symmetric) """ Fused version of `default_per_channel_weight_fake_quant`, with improved performance. """ def _is_fake_quant_script_module(mod): ''' Returns true if given mod is an instance of FakeQuantize script module. ''' if isinstance(mod, torch.jit.RecursiveScriptModule): # qualified name looks like '__torch__.torch.ao.quantization.fake_quantize.___torch_mangle_2.FakeQuantize' suffix = mod._c.qualified_name.split('.', 1)[1] name = re.sub(r'\.___torch_mangle_\d+', '', suffix) return name == 'torch.ao.quantization.fake_quantize.FakeQuantize' or \ name == 'torch.ao.quantization.fake_quantize.FusedMovingAvgObsFakeQuantize' return False
[docs]def disable_fake_quant(mod): """ Disable fake quantization for this module, if applicable. Example usage:: # model is any PyTorch model model.apply(torch.ao.quantization.disable_fake_quant) """ if isinstance(mod, FakeQuantizeBase) or _is_fake_quant_script_module(mod): mod.disable_fake_quant()
[docs]def enable_fake_quant(mod): """ Enable fake quantization for this module, if applicable. Example usage:: # model is any PyTorch model model.apply(torch.ao.quantization.enable_fake_quant) """ if isinstance(mod, FakeQuantizeBase) or _is_fake_quant_script_module(mod): mod.enable_fake_quant()
[docs]def disable_observer(mod): """ Disable observation for this module, if applicable. Example usage:: # model is any PyTorch model model.apply(torch.ao.quantization.disable_observer) """ if isinstance(mod, FakeQuantizeBase) or _is_fake_quant_script_module(mod): mod.disable_observer()
[docs]def enable_observer(mod): """ Enable observation for this module, if applicable. Example usage:: # model is any PyTorch model model.apply(torch.ao.quantization.enable_observer) """ if isinstance(mod, FakeQuantizeBase) or _is_fake_quant_script_module(mod): mod.enable_observer()

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