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# Copyright (c) Microsoft Corporation.
# Licensed under the MIT license.
import types
import logging
import torch
from . import default_layers
_logger = logging.getLogger(__name__)
class LayerInfo:
def __init__(self, name, module):
self.module = module
self.name = name
self.type = type(module).__name__
def _setattr(model, name, module):
name_list = name.split(".")
for name in name_list[:-1]:
model = getattr(model, name)
setattr(model, name_list[-1], module)
class Compressor:
"""
Abstract base PyTorch compressor
"""
def __init__(self, model, config_list, optimizer=None):
"""
Record necessary info in class members
Parameters
----------
model : pytorch model
the model user wants to compress
config_list : list
the configurations that users specify for compression
optimizer: pytorch optimizer
optimizer used to train the model
"""
assert isinstance(model, torch.nn.Module)
self.validate_config(model, config_list)
self.bound_model = model
self.config_list = config_list
self.optimizer = optimizer
self.modules_to_compress = None
self.modules_wrapper = []
self.is_wrapped = False
self._fwd_hook_handles = {}
self._fwd_hook_id = 0
self.reset()
if not self.modules_wrapper:
_logger.warning('Nothing is configured to compress, please check your model and config_list')
def validate_config(self, model, config_list):
"""
subclass can optionally implement this method to check if config_list if valid
"""
pass
def reset(self, checkpoint=None):
"""
reset model state dict and model wrapper
"""
self._unwrap_model()
if checkpoint is not None:
self.bound_model.load_state_dict(checkpoint)
self.modules_to_compress = None
self.modules_wrapper = []
for layer, config in self._detect_modules_to_compress():
wrapper = self._wrap_modules(layer, config)
self.modules_wrapper.append(wrapper)
self._wrap_model()
def _detect_modules_to_compress(self):
"""
detect all modules should be compressed, and save the result in `self.modules_to_compress`.
The model will be instrumented and user should never edit it after calling this method.
"""
if self.modules_to_compress is None:
self.modules_to_compress = []
for name, module in self.bound_model.named_modules():
if module == self.bound_model:
continue
layer = LayerInfo(name, module)
config = self.select_config(layer)
if config is not None:
self.modules_to_compress.append((layer, config))
return self.modules_to_compress
def _wrap_model(self):
"""
wrap all modules that needed to be compressed
"""
for wrapper in reversed(self.get_modules_wrapper()):
_setattr(self.bound_model, wrapper.name, wrapper)
self.is_wrapped = True
def _unwrap_model(self):
"""
unwrap all modules that needed to be compressed
"""
for wrapper in self.get_modules_wrapper():
_setattr(self.bound_model, wrapper.name, wrapper.module)
self.is_wrapped = False
def compress(self):
"""
Compress the model with algorithm implemented by subclass.
The model will be instrumented and user should never edit it after calling this method.
`self.modules_to_compress` records all the to-be-compressed layers
Returns
-------
torch.nn.Module
model with specified modules compressed.
"""
return self.bound_model
def set_wrappers_attribute(self, name, value):
"""
To register attributes used in wrapped module's forward method.
If the type of the value is Torch.tensor, then this value is registered as a buffer in wrapper,
which will be saved by model.state_dict. Otherwise, this value is just a regular variable in wrapper.
Parameters
----------
name : str
name of the variable
value: any
value of the variable
"""
for wrapper in self.get_modules_wrapper():
if isinstance(value, torch.Tensor):
wrapper.register_buffer(name, value.clone())
else:
setattr(wrapper, name, value)
def get_modules_to_compress(self):
"""
To obtain all the to-be-compressed modules.
Returns
-------
list
a list of the layers, each of which is a tuple (`layer`, `config`),
`layer` is `LayerInfo`, `config` is a `dict`
"""
return self.modules_to_compress
def get_modules_wrapper(self):
"""
To obtain all the wrapped modules.
Returns
-------
list
a list of the wrapped modules
"""
return self.modules_wrapper
def select_config(self, layer):
"""
Find the configuration for `layer` by parsing `self.config_list`
Parameters
----------
layer : LayerInfo
one layer
Returns
-------
config or None
the retrieved configuration for this layer, if None, this layer should
not be compressed
"""
ret = None
for config in self.config_list:
config = config.copy()
# expand config if key `default` is in config['op_types']
if 'op_types' in config and 'default' in config['op_types']:
expanded_op_types = []
for op_type in config['op_types']:
if op_type == 'default':
expanded_op_types.extend(default_layers.weighted_modules)
else:
expanded_op_types.append(op_type)
config['op_types'] = expanded_op_types
# check if condition is satisified
if 'op_types' in config and layer.type not in config['op_types']:
continue
if 'op_names' in config and layer.name not in config['op_names']:
continue
ret = config
if ret is None or 'exclude' in ret:
return None
return ret
def update_epoch(self, epoch):
"""
If user want to update model every epoch, user can override this method.
This method should be called at the beginning of each epoch
Parameters
----------
epoch : num
the current epoch number
"""
pass
def _wrap_modules(self, layer, config):
"""
This method is implemented in the subclasses, i.e., `Pruner` and `Quantizer`
Parameters
----------
layer : LayerInfo
the layer to instrument the compression operation
config : dict
the configuration for compressing this layer
"""
raise NotImplementedError()
def add_activation_collector(self, collector):
self._fwd_hook_id += 1
self._fwd_hook_handles[self._fwd_hook_id] = []
for wrapper in self.get_modules_wrapper():
handle = wrapper.register_forward_hook(collector)
self._fwd_hook_handles[self._fwd_hook_id].append(handle)
return self._fwd_hook_id
def remove_activation_collector(self, fwd_hook_id):
if fwd_hook_id not in self._fwd_hook_handles:
raise ValueError("%s is not a valid collector id" % str(fwd_hook_id))
for handle in self._fwd_hook_handles[fwd_hook_id]:
handle.remove()
del self._fwd_hook_handles[fwd_hook_id]
def patch_optimizer(self, *tasks):
def patch_step(old_step):
def new_step(_, *args, **kwargs):
# call origin optimizer step method
output = old_step(*args, **kwargs)
# calculate mask
for task in tasks:
task()
return output
return new_step
if self.optimizer is not None:
self.optimizer.step = types.MethodType(patch_step(self.optimizer.step), self.optimizer)
class PrunerModuleWrapper(torch.nn.Module):
def __init__(self, module, module_name, module_type, config, pruner):
"""
Wrap an module to enable data parallel, forward method customization and buffer registeration.
Parameters
----------
module : pytorch module
the module user wants to compress
config : dict
the configurations that users specify for compression
module_name : str
the name of the module to compress, wrapper module shares same name
module_type : str
the type of the module to compress
pruner ： Pruner
the pruner used to calculate mask
"""
super().__init__()
# origin layer information
self.module = module
self.name = module_name
self.type = module_type
# config and pruner
self.config = config
self.pruner = pruner
# register buffer for mask
self.register_buffer("weight_mask", torch.ones(self.module.weight.shape))
if hasattr(self.module, 'bias') and self.module.bias is not None:
self.register_buffer("bias_mask", torch.ones(self.module.bias.shape))
else:
self.register_buffer("bias_mask", None)
def forward(self, *inputs):
# apply mask to weight, bias
self.module.weight.data = self.module.weight.data.mul_(self.weight_mask)
if hasattr(self.module, 'bias') and self.module.bias is not None:
self.module.bias.data = self.module.bias.data.mul_(self.bias_mask)
return self.module(*inputs)
class Pruner(Compressor):
"""
Prune to an exact pruning level specification
Attributes
----------
mask_dict : dict
Dictionary for saving masks, `key` should be layer name and
`value` should be a tensor which has the same shape with layer's weight
"""
def __init__(self, model, config_list, optimizer=None):
super().__init__(model, config_list, optimizer)
if optimizer is not None:
self.patch_optimizer(self.update_mask)
def compress(self):
self.update_mask()
return self.bound_model
def update_mask(self):
for wrapper_idx, wrapper in enumerate(self.get_modules_wrapper()):
masks = self.calc_mask(wrapper, wrapper_idx=wrapper_idx)
if masks is not None:
for k in masks:
assert hasattr(wrapper, k), "there is no attribute '%s' in wrapper" % k
setattr(wrapper, k, masks[k])
def calc_mask(self, wrapper, **kwargs):
"""
Pruners should overload this method to provide mask for weight tensors.
The mask must have the same shape and type comparing to the weight.
It will be applied with `mul()` operation on the weight.
This method is effectively hooked to `forward()` method of the model.
Parameters
----------
wrapper : Module
calculate mask for `wrapper.module`'s weight
"""
raise NotImplementedError("Pruners must overload calc_mask()")
def _wrap_modules(self, layer, config):
"""
Create a wrapper module to replace the original one.
Parameters
----------
layer : LayerInfo
the layer to instrument the mask
config : dict
the configuration for generating the mask
"""
_logger.debug("Module detected to compress : %s.", layer.name)
wrapper = PrunerModuleWrapper(layer.module, layer.name, layer.type, config, self)
assert hasattr(layer.module, 'weight'), "module %s does not have 'weight' attribute" % layer.name
# move newly registered buffers to the same device of weight
wrapper.to(layer.module.weight.device)
return wrapper
def export_model(self, model_path, mask_path=None, onnx_path=None, input_shape=None, device=None):
"""
Export pruned model weights, masks and onnx model(optional)
Parameters
----------
model_path : str
path to save pruned model state_dict
mask_path : str
(optional) path to save mask dict
onnx_path : str
(optional) path to save onnx model
input_shape : list or tuple
input shape to onnx model
device : torch.device
device of the model, used to place the dummy input tensor for exporting onnx file.
the tensor is placed on cpu if ```device``` is None
"""
assert model_path is not None, 'model_path must be specified'
mask_dict = {}
self._unwrap_model() # used for generating correct state_dict name without wrapper state
for wrapper in self.get_modules_wrapper():
weight_mask = wrapper.weight_mask
bias_mask = wrapper.bias_mask
if weight_mask is not None:
mask_sum = weight_mask.sum().item()
mask_num = weight_mask.numel()
_logger.debug('Layer: %s Sparsity: %.4f', wrapper.name, 1 - mask_sum / mask_num)
wrapper.module.weight.data = wrapper.module.weight.data.mul(weight_mask)
if bias_mask is not None:
wrapper.module.bias.data = wrapper.module.bias.data.mul(bias_mask)
# save mask to dict
mask_dict[wrapper.name] = {"weight": weight_mask, "bias": bias_mask}
torch.save(self.bound_model.state_dict(), model_path)
_logger.info('Model state_dict saved to %s', model_path)
if mask_path is not None:
torch.save(mask_dict, mask_path)
_logger.info('Mask dict saved to %s', mask_path)
if onnx_path is not None:
assert input_shape is not None, 'input_shape must be specified to export onnx model'
# input info needed
if device is None:
device = torch.device('cpu')
input_data = torch.Tensor(*input_shape)
torch.onnx.export(self.bound_model, input_data.to(device), onnx_path)
_logger.info('Model in onnx with input shape %s saved to %s', input_data.shape, onnx_path)
self._wrap_model()
def load_model_state_dict(self, model_state):
"""
Load the state dict saved from unwrapped model.
Parameters:
-----------
model_state : dict
state dict saved from unwrapped model
"""
if self.is_wrapped:
self._unwrap_model()
self.bound_model.load_state_dict(model_state)
self._wrap_model()
else:
self.bound_model.load_state_dict(model_state)
class QuantizerModuleWrapper(torch.nn.Module):
def __init__(self, module, module_name, module_type, config, quantizer):
"""
Wrap an module to enable data parallel, forward method customization and buffer registeration.
Parameters
----------
module : pytorch module
the module user wants to compress
config : dict
the configurations that users specify for compression
module_name : str
the name of the module to compress, wrapper module shares same name
module_type : str
the type of the module to compress
quantizer ：quantizer
the quantizer used to calculate mask
"""
super().__init__()
# origin layer information
self.module = module
self.name = module_name
self.type = module_type
# config and pruner
self.config = config
self.quantizer = quantizer
# register buffer and parameter
# old_weight is used to store origin weight and weight is used to store quantized weight
# the reason why weight is buffer instead of parameter is because in pytorch parameter is used as leaf
# if weight is leaf , then old_weight can not be updated.
if 'weight' in config['quant_types']:
if not _check_weight(self.module):
_logger.warning('Module %s does not have parameter "weight"', self.name)
else:
self.module.register_parameter('old_weight', torch.nn.Parameter(self.module.weight))
delattr(self.module, 'weight')
self.module.register_buffer('weight', self.module.old_weight)
def forward(self, *inputs):
if 'input' in self.config['quant_types']:
inputs = self.quantizer.quant_grad.apply(
inputs,
QuantType.QUANT_INPUT,
self)
if 'weight' in self.config['quant_types'] and _check_weight(self.module):
self.quantizer.quant_grad.apply(
self.module.old_weight,
QuantType.QUANT_WEIGHT,
self)
result = self.module(*inputs)
else:
result = self.module(*inputs)
if 'output' in self.config['quant_types']:
result = self.quantizer.quant_grad.apply(
result,
QuantType.QUANT_OUTPUT,
self)
return result
return result
class Quantizer(Compressor):
"""
Base quantizer for pytorch quantizer
"""
def __init__(self, model, config_list, optimizer=None):
super().__init__(model, config_list, optimizer)
self.quant_grad = QuantGrad
if self.optimizer is not None:
self.patch_optimizer(self.step_with_optimizer)
for wrapper in self.get_modules_wrapper():
if 'weight' in wrapper.config['quant_types']:
# old_weight is registered to keep track of weight before quantization
# and it is trainable, therefore, it should be added to optimizer.
self.optimizer.add_param_group({"params": wrapper.module.old_weight})
def quantize_weight(self, weight, wrapper, **kwargs):
"""
quantize should overload this method to quantize weight.
This method is effectively hooked to :meth:`forward` of the model.
Parameters
----------
weight : Tensor
weight that needs to be quantized
wrapper : QuantizerModuleWrapper
the wrapper for origin module
"""
raise NotImplementedError('Quantizer must overload quantize_weight()')
def quantize_output(self, output, wrapper, **kwargs):
"""
quantize should overload this method to quantize output.
This method is effectively hooked to :meth:`forward` of the model.
Parameters
----------
output : Tensor
output that needs to be quantized
wrapper : QuantizerModuleWrapper
the wrapper for origin module
"""
raise NotImplementedError('Quantizer must overload quantize_output()')
def quantize_input(self, *inputs, wrapper, **kwargs):
"""
quantize should overload this method to quantize input.
This method is effectively hooked to :meth:`forward` of the model.
Parameters
----------
inputs : Tensor
inputs that needs to be quantized
wrapper : QuantizerModuleWrapper
the wrapper for origin module
"""
raise NotImplementedError('Quantizer must overload quantize_input()')
def _wrap_modules(self, layer, config):
"""
Create a wrapper forward function to replace the original one.
Parameters
----------
layer : LayerInfo
the layer to instrument the mask
config : dict
the configuration for quantization
"""
assert 'quant_types' in config, 'must provide quant_types in config'
assert isinstance(config['quant_types'], list), 'quant_types must be list type'
assert 'quant_bits' in config, 'must provide quant_bits in config'
assert isinstance(config['quant_bits'], int) or isinstance(config['quant_bits'], dict), 'quant_bits must be dict type or int type'
if isinstance(config['quant_bits'], dict):
for quant_type in config['quant_types']:
assert quant_type in config['quant_bits'], 'bits length for %s must be specified in quant_bits dict' % quant_type
return QuantizerModuleWrapper(layer.module, layer.name, layer.type, config, self)
def step_with_optimizer(self):
pass
class QuantType:
"""
Enum class for quantization type.
"""
QUANT_INPUT = 0
QUANT_WEIGHT = 1
QUANT_OUTPUT = 2
class QuantGrad(torch.autograd.Function):
"""
Base class for overriding backward function of quantization operation.
"""
@staticmethod
def quant_backward(tensor, grad_output, quant_type):
"""
This method should be overrided by subclass to provide customized backward function,
default implementation is Straight-Through Estimator
Parameters
----------
tensor : Tensor
input of quantization operation
grad_output : Tensor
gradient of the output of quantization operation
quant_type : QuantType
the type of quantization, it can be `QuantType.QUANT_INPUT`, `QuantType.QUANT_WEIGHT`, `QuantType.QUANT_OUTPUT`,
you can define different behavior for different types.
Returns
-------
tensor
gradient of the input of quantization operation
"""
return grad_output
@staticmethod
def forward(ctx, tensor, quant_type, wrapper, **kwargs):
ctx.save_for_backward(tensor, torch.Tensor([quant_type]))
if quant_type == QuantType.QUANT_INPUT:
return wrapper.quantizer.quantize_input(tensor, wrapper, **kwargs)
elif quant_type == QuantType.QUANT_WEIGHT:
return wrapper.quantizer.quantize_weight(wrapper, **kwargs)
elif quant_type == QuantType.QUANT_OUTPUT:
return wrapper.quantizer.quantize_output(tensor, wrapper, **kwargs)
else:
raise ValueError("unrecognized QuantType.")
@classmethod
def backward(cls, ctx, grad_output):
tensor, quant_type = ctx.saved_variables
output = cls.quant_backward(tensor, grad_output, quant_type)
return output, None, None, None
def _check_weight(module):
try:
return isinstance(module.weight.data, torch.Tensor)
except AttributeError:
return False
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