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Model-Optimizer/modelopt/torch/quantization/plugins/peft.py
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2025-07-31 22:48:09 +05:30

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# SPDX-FileCopyrightText: Copyright (c) 2024 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Support quantization for peft LoRA linear layers."""
import torch.nn.functional as F
from peft.tuners.lora.layer import Linear as LoraLinear
from modelopt.torch.quantization.qtensor.base_qtensor import QTensorWrapper
from ..nn import QuantModule, QuantModuleRegistry, TensorQuantizer
__all__ = []
@QuantModuleRegistry.register({LoraLinear: "LoraLinear"})
class _QuantLoraLinear(QuantModule):
def _setup(self):
self.input_quantizer = TensorQuantizer()
self.weight_quantizer = TensorQuantizer()
self.output_quantizer = TensorQuantizer()
def forward(self, x, *args, **kwargs):
adapter_names = kwargs.pop("adapter_names", None)
if self.disable_adapters or adapter_names is not None or self.merged:
return super().forward(x, args, kwargs)
x = self.input_quantizer(x)
weight = self.base_layer.weight
is_compressed = isinstance(weight, QTensorWrapper)
if not is_compressed:
for active_adapter in self.active_adapters:
if active_adapter not in self.lora_A.keys(): # noqa: SIM118
continue
lora_a = self.lora_A[active_adapter]
lora_b = self.lora_B[active_adapter]
scaling = self.scaling[active_adapter]
if not self.use_dora[active_adapter]:
weight = weight + scaling * lora_b.weight @ lora_a.weight
else:
raise NotImplementedError("dora not implemented")
weight = self.weight_quantizer(weight)
output = F.linear(x, weight, self.base_layer.bias)
else:
# For compressed weights, compute base output and LoRA outputs separately
base_output = self.base_layer(x)
# Only compute LoRA outputs if there are active adapters
if self.active_adapters:
# Start with zero LoRA output
lora_output = None
for active_adapter in self.active_adapters:
if active_adapter not in self.lora_A.keys(): # noqa: SIM118
continue
lora_a = self.lora_A[active_adapter]
lora_b = self.lora_B[active_adapter]
scaling = self.scaling[active_adapter]
if not self.use_dora[active_adapter]:
# Compute LoRA output step by step to maintain gradient flow
lora_a_output = F.linear(x, lora_a.weight)
lora_b_output = F.linear(lora_a_output, lora_b.weight)
adapter_output = scaling * lora_b_output
lora_output = (
adapter_output if lora_output is None else lora_output + adapter_output
)
output = base_output + lora_output
else:
output = base_output
output = self.output_quantizer(output)
return output