TextBrewer is a PyTorch-based model distillation toolkit for natural language processing. It includes various distillation techniques from both NLP and CV field and provides an easy-to-use distillation framework, which allows users to quickly experiment with the state-of-the-art distillation methods to compress the model with a relatively small sacrifice in the performance, increasing the inference speed and reducing the memory usage.
Check our paper through ACL Anthology or arXiv pre-print.
Dec 17, 2021
- We have released a model pruning toolkit TextPruner. Check https://github.com/airaria/TextPruner
Oct 24, 2021
- We propose the first pre-trained language model that specifically focusing on Chinese minority languages. Check:https://github.com/ymcui/Chinese-Minority-PLM
Jul 8, 2021
- New examples with Transformers 4
- The current examples (exmaples/) have been written with old versions of Transformers and they may cause some confusions and bugs. We rewrite the examples with Transformers 4 in Jupyter Notebooks, which are easy to follow and learn.
- The new examples can be found at examples/notebook_examples. See Examples for details.
Mar 1, 2021
-
BERT-EMD and custom distiller
- We added an experiment with BERT-EMD in the MNLI exmaple. BERT-EMD allows each intermediate student layer to learn from any intermediate teacher layers adaptively, based on optimizing Earth Mover’s Distance. So there is no need to specify the matching scheme.
- We have written a new EMDDistiller to perform BERT-EMD. It demonstrates how to write a custom distiller.
-
updated MNLI example
- We removed the pretrained_pytorch_bert and used transformers library instead in all the MNLI examples.
Click here to see old news
Nov 11, 2020
-
Updated to 0.2.1:
-
More flexible distillation: Supports feeding different batches to the student and teacher. It means the batches for the student and teacher no longer need to be the same. It can be used for distilling models with different vocabularies (e.g., from RoBERTa to BERT).
-
Faster distillation: Users now can pre-compute and cache the teacher outputs, then feed the cache to the distiller to save teacher's forward pass time.
See Feed Different batches to Student and Teacher, Feed Cached Values for details of the above features.
-
MultiTaskDistiller
now supports intermediate feature matching loss. -
Tensorboard now records more detailed losses (KD loss, hard label loss, matching losses...).
See details in releases.
-
August 27, 2020
We are happy to announce that our model is on top of GLUE benchmark, check leaderboard.
Aug 24, 2020
- Updated to 0.2.0.1:
- fixed bugs in
MultiTaskDistiller
and training loops.
- fixed bugs in
Jul 29, 2020
- Updated to 0.2.0:
- Added the support for distributed data-parallel training with
DistributedDataParallel
:TrainingConfig
now accpects thelocal_rank
argument. See the documentation ofTrainingConfig
for detail.
- Added the support for distributed data-parallel training with
- Added an example of distillation on the Chinese NER task to demonstrate distributed data-parallel training. See examples/msra_ner_example.
Jul 14, 2020
- Updated to 0.1.10:
- Now supports mixed precision training with Apex! Just set
fp16
toTrue
inTrainingConfig
. See the documentation ofTrainingConfig
for detail. - Added
data_parallel
option inTrainingConfig
to enable data parallel training and mixed precision training work together.
- Now supports mixed precision training with Apex! Just set
Apr 26, 2020
- Added Chinese NER task (MSRA NER) results.
- Added results for distilling to T12-nano model, which has a similar strcuture to Electra-small.
- Updated some results of CoNLL-2003, CMRC 2018 and DRCD.
Apr 22, 2020
- Updated to 0.1.9 (added cache option which speeds up distillation; fixed some bugs). See details in releases.
- Added experimential results for distilling Electra-base to Electra-small on Chinese tasks.
- TextBrewer has been accepted by ACL 2020 as a demo paper, please use our new bib entry.
Mar 17, 2020
- Added CoNLL-2003 English NER distillation example. See examples/conll2003_example.
Mar 11, 2020
- Updated to 0.1.8 (Improvements on TrainingConfig and train method). See details in releases.
Mar 2, 2020
- Initial public version 0.1.7 has been released. See details in releases.
Section | Contents |
---|---|
Introduction | Introduction to TextBrewer |
Installation | How to install |
Workflow | Two stages of TextBrewer workflow |
Quickstart | Example: distilling BERT-base to a 3-layer BERT |
Experiments | Distillation experiments on typical English and Chinese datasets |
Core Concepts | Brief explanations of the core concepts in TextBrewer |
FAQ | Frequently asked questions |
Known Issues | Known issues |
Citation | Citation to TextBrewer |
Follow Us | - |
Textbrewer is designed for the knowledge distillation of NLP models. It provides various distillation methods and offers a distillation framework for quickly setting up experiments.
The main features of TextBrewer are:
- Wide-support: it supports various model architectures (especially transformer-based models)
- Flexibility: design your own distillation scheme by combining different techniques; it also supports user-defined loss functions, modules, etc.
- Easy-to-use: users don't need to modify the model architectures
- Built for NLP: it is suitable for a wide variety of NLP tasks: text classification, machine reading comprehension, sequence labeling, ...
TextBrewer currently is shipped with the following distillation techniques:
- Mixed soft-label and hard-label training
- Dynamic loss weight adjustment and temperature adjustment
- Various distillation loss functions: hidden states MSE, attention-matrix-based loss, neuron selectivity transfer, ...
- Freely adding intermediate features matching losses
- Multi-teacher distillation
- ...
TextBrewer includes:
- Distillers: the cores of distillation. Different distillers perform different distillation modes. There are GeneralDistiller, MultiTeacherDistiller, BasicTrainer, etc.
- Configurations and presets: Configuration classes for training and distillation, and predefined distillation loss functions and strategies.
- Utilities: auxiliary tools such as model parameters analysis.
To start distillation, users need to provide
- the models (the trained teacher model and the un-trained student model)
- datasets and experiment configurations
TextBrewer has achieved impressive results on several typical NLP tasks. See Experiments.
See Full Documentation for detailed usages.
-
Requirements
- Python >= 3.6
- PyTorch >= 1.1.0
- TensorboardX or Tensorboard
- NumPy
- tqdm
- Transformers >= 2.0 (optional, used by some examples)
- Apex == 0.1.0 (optional, mixed precision training)
-
Install from PyPI
pip install textbrewer
-
Install from the Github source
git clone https://github.com/airaria/TextBrewer.git pip install ./textbrewer
-
Stage 1: Preparation:
- Train the teacher model
- Define and initialize the student model
- Construct a dataloader, an optimizer, and a learning rate scheduler
-
Stage 2: Distillation with TextBrewer:
- Construct a TraningConfig and a DistillationConfig, initialize a distiller
- Define an adaptor and a callback. The adaptor is used for adaptation of model inputs and outputs. The callback is called by the distiller during training
- Call the train method of the distiller
Here we show the usage of TextBrewer by distilling BERT-base to a 3-layer BERT.
Before distillation, we assume users have provided:
- A trained teacher model
teacher_model
(BERT-base) and a to-be-trained student modelstudent_model
(3-layer BERT). - a
dataloader
of the dataset, anoptimizer
and a learning rate builder or classscheduler_class
and its args dictscheduler_dict
.
Distill with TextBrewer:
import textbrewer
from textbrewer import GeneralDistiller
from textbrewer import TrainingConfig, DistillationConfig
# Show the statistics of model parameters
print("\nteacher_model's parametrers:")
result, _ = textbrewer.utils.display_parameters(teacher_model,max_level=3)
print (result)
print("student_model's parametrers:")
result, _ = textbrewer.utils.display_parameters(student_model,max_level=3)
print (result)
# Define an adaptor for interpreting the model inputs and outputs
def simple_adaptor(batch, model_outputs):
# The second and third elements of model outputs are the logits and hidden states
return {'logits': model_outputs[1],
'hidden': model_outputs[2]}
# Training configuration
train_config = TrainingConfig()
# Distillation configuration
# Matching different layers of the student and the teacher
distill_config = DistillationConfig(
intermediate_matches=[
{'layer_T':0, 'layer_S':0, 'feature':'hidden', 'loss': 'hidden_mse','weight' : 1},
{'layer_T':8, 'layer_S':2, 'feature':'hidden', 'loss': 'hidden_mse','weight' : 1}])
# Build distiller
distiller = GeneralDistiller(
train_config=train_config, distill_config = distill_config,
model_T = teacher_model, model_S = student_model,
adaptor_T = simple_adaptor, adaptor_S = simple_adaptor)
# Start!
with distiller:
distiller.train(optimizer, dataloader, num_epochs=1, scheduler_class=scheduler_class, scheduler_args = scheduler_args, callback=None)
-
Notebook examples with Transformers 4
- examples/notebook_examples/sst2.ipynb (English): training and distilling BERT on SST-2, an English sentence classification task.
- examples/notebook_examples/msra_ner.ipynb (Chinese): training and distilling BERT on MSRA NER, a Chinese sequence labeling task.
- examples/notebook_examples/sqaudv1.1.ipynb (English): training and distilling BERT on SQuAD 1.1, an English MRC task.
-
examples/random_token_example : a simple runnable toy example which demonstrates the usage of TextBrewer. This example performs distillation on the text classification task with random tokens as inputs.
-
examples/cmrc2018_example (Chinese): distillation on CMRC 2018, a Chinese MRC task, using DRCD as data augmentation.
-
examples/mnli_example (English): distillation on MNLI, an English sentence-pair classification task. This example also shows how to perform multi-teacher distillation.
-
examples/conll2003_example (English): distillation on CoNLL-2003 English NER task, which is in form of sequence labeling.
-
examples/msra_ner_example (Chinese): This example distills a Chinese-ELECTRA-base model on the MSRA NER task with distributed data-parallel training(single node, multi-GPU).
We have performed distillation experiments on several typical English and Chinese NLP datasets. The setups and configurations are listed below.
- For English tasks, the teacher model is BERT-base-cased.
- For Chinese tasks, the teacher models are RoBERTa-wwm-ext and Electra-base released by the Joint Laboratory of HIT and iFLYTEK Research.
We have tested different student models. To compare with public results, the student models are built with standard transformer blocks except for BiGRU which is a single-layer bidirectional GRU. The architectures are listed below. Note that the number of parameters includes the embedding layer but does not include the output layer of each specific task.
Model | #Layers | Hidden size | Feed-forward size | #Params | Relative size |
---|---|---|---|---|---|
BERT-base-cased (teacher) | 12 | 768 | 3072 | 108M | 100% |
T6 (student) | 6 | 768 | 3072 | 65M | 60% |
T3 (student) | 3 | 768 | 3072 | 44M | 41% |
T3-small (student) | 3 | 384 | 1536 | 17M | 16% |
T4-Tiny (student) | 4 | 312 | 1200 | 14M | 13% |
T12-nano (student) | 12 | 256 | 1024 | 17M | 16% |
BiGRU (student) | - | 768 | - | 31M | 29% |
Model | #Layers | Hidden size | Feed-forward size | #Params | Relative size |
---|---|---|---|---|---|
RoBERTa-wwm-ext (teacher) | 12 | 768 | 3072 | 102M | 100% |
Electra-base (teacher) | 12 | 768 | 3072 | 102M | 100% |
T3 (student) | 3 | 768 | 3072 | 38M | 37% |
T3-small (student) | 3 | 384 | 1536 | 14M | 14% |
T4-Tiny (student) | 4 | 312 | 1200 | 11M | 11% |
Electra-small (student) | 12 | 256 | 1024 | 12M | 12% |
- T6 architecture is the same as DistilBERT[1], BERT6-PKD[2], and BERT-of-Theseus[3].
- T4-tiny architecture is the same as TinyBERT[4].
- T3 architecure is the same as BERT3-PKD[2].
distill_config = DistillationConfig(temperature = 8, intermediate_matches = matches)
# Others arguments take the default values
matches
are differnt for different models:
Model | matches |
---|---|
BiGRU | None |
T6 | L6_hidden_mse + L6_hidden_smmd |
T3 | L3_hidden_mse + L3_hidden_smmd |
T3-small | L3n_hidden_mse + L3_hidden_smmd |
T4-Tiny | L4t_hidden_mse + L4_hidden_smmd |
T12-nano | small_hidden_mse + small_hidden_smmd |
Electra-small | small_hidden_mse + small_hidden_smmd |
The definitions of matches are at examples/matches/matches.py.
We use GeneralDistiller in all the distillation experiments.
- Learning rate is 1e-4 (unless otherwise specified).
- We train all the models for 30~60 epochs.
We experiment on the following typical English datasets:
Dataset | Task type | Metrics | #Train | #Dev | Note |
---|---|---|---|---|---|
MNLI | text classification | m/mm Acc | 393K | 20K | sentence-pair 3-class classification |
SQuAD 1.1 | reading comprehension | EM/F1 | 88K | 11K | span-extraction machine reading comprehension |
CoNLL-2003 | sequence labeling | F1 | 23K | 6K | named entity recognition |
We list the public results from DistilBERT, BERT-PKD, BERT-of-Theseus, TinyBERT and our results below for comparison.
Public results:
Model (public) | MNLI | SQuAD | CoNLL-2003 |
---|---|---|---|
DistilBERT (T6) | 81.6 / 81.1 | 78.1 / 86.2 | - |
BERT6-PKD (T6) | 81.5 / 81.0 | 77.1 / 85.3 | - |
BERT-of-Theseus (T6) | 82.4/ 82.1 | - | - |
BERT3-PKD (T3) | 76.7 / 76.3 | - | - |
TinyBERT (T4-tiny) | 82.8 / 82.9 | 72.7 / 82.1 | - |
Our results:
Model (ours) | MNLI | SQuAD | CoNLL-2003 |
---|---|---|---|
BERT-base-cased (teacher) | 83.7 / 84.0 | 81.5 / 88.6 | 91.1 |
BiGRU | - | - | 85.3 |
T6 | 83.5 / 84.0 | 80.8 / 88.1 | 90.7 |
T3 | 81.8 / 82.7 | 76.4 / 84.9 | 87.5 |
T3-small | 81.3 / 81.7 | 72.3 / 81.4 | 78.6 |
T4-tiny | 82.0 / 82.6 | 75.2 / 84.0 | 89.1 |
T12-nano | 83.2 / 83.9 | 79.0 / 86.6 | 89.6 |
Note:
- The equivalent model structures of public models are shown in the brackets after their names.
- When distilling to T4-tiny, NewsQA is used for data augmentation on SQuAD and HotpotQA is used for data augmentation on CoNLL-2003.
- When distilling to T12-nano, HotpotQA is used for data augmentation on CoNLL-2003.
We experiment on the following typical Chinese datasets:
Dataset | Task type | Metrics | #Train | #Dev | Note |
---|---|---|---|---|---|
XNLI | text classification | Acc | 393K | 2.5K | Chinese translation version of MNLI |
LCQMC | text classification | Acc | 239K | 8.8K | sentence-pair matching, binary classification |
CMRC 2018 | reading comprehension | EM/F1 | 10K | 3.4K | span-extraction machine reading comprehension |
DRCD | reading comprehension | EM/F1 | 27K | 3.5K | span-extraction machine reading comprehension (Traditional Chinese) |
MSRA NER | sequence labeling | F1 | 45K | 3.4K (#Test) | Chinese named entity recognition |
The results are listed below.
Model | XNLI | LCQMC | CMRC 2018 | DRCD |
---|---|---|---|---|
RoBERTa-wwm-ext (teacher) | 79.9 | 89.4 | 68.8 / 86.4 | 86.5 / 92.5 |
T3 | 78.4 | 89.0 | 66.4 / 84.2 | 78.2 / 86.4 |
T3-small | 76.0 | 88.1 | 58.0 / 79.3 | 75.8 / 84.8 |
T4-tiny | 76.2 | 88.4 | 61.8 / 81.8 | 77.3 / 86.1 |
Model | XNLI | LCQMC | CMRC 2018 | DRCD | MSRA NER |
---|---|---|---|---|---|
Electra-base (teacher)) | 77.8 | 89.8 | 65.6 / 84.7 | 86.9 / 92.3 | 95.14 |
Electra-small | 77.7 | 89.3 | 66.5 / 84.9 | 85.5 / 91.3 | 93.48 |
Note:
- Learning rate decay is not used in distillation on CMRC 2018 and DRCD.
- CMRC 2018 and DRCD take each other as the augmentation dataset in the distillation.
- The settings of training Electra-base teacher model can be found at Chinese-ELECTRA.
- Electra-small student model is initialized with the pretrained weights.
TrainingConfig
: configuration related to general deep learning model trainingDistillationConfig
: configuration related to distillation methods
Distillers are in charge of conducting the actual experiments. The following distillers are available:
BasicDistiller
: single-teacher single-task distillation, provides basic distillation strategies.GeneralDistiller
(Recommended): single-teacher single-task distillation, supports intermediate features matching. Recommended most of the time.MultiTeacherDistiller
: multi-teacher distillation, which distills multiple teacher models (of the same task) into a single student model. This class doesn't support Intermediate features matching.MultiTaskDistiller
: multi-task distillation, which distills multiple teacher models (of different tasks) into a single student.BasicTrainer
: Supervised training a single model on a labeled dataset, not for distillation. It can be used to train a teacher model.
In TextBrewer, there are two functions that should be implemented by users: callback and adaptor.
At each checkpoint, after saving the student model, the callback function will be called by the distiller. A callback can be used to evaluate the performance of the student model at each checkpoint.
It converts the model inputs and outputs to the specified format so that they could be recognized by the distiller, and distillation losses can be computed. At each training step, batch and model outputs will be passed to the adaptor; the adaptor re-organizes the data and returns a dictionary.
For more details, see the explanations in Full Documentation.
Q: How to initialize the student model?
A: The student model could be randomly initialized (i.e., with no prior knowledge) or be initialized by pre-trained weights. For example, when distilling a BERT-base model to a 3-layer BERT, you could initialize the student model with RBT3 (for Chinese tasks) or the first three layers of BERT (for English tasks) to avoid cold start problem. We recommend that users use pre-trained student models whenever possible to fully take advantage of large-scale pre-training.
Q: How to set training hyperparameters for the distillation experiments?
A: Knowledge distillation usually requires more training epochs and larger learning rate than training on the labeled dataset. For example, training SQuAD on BERT-base usually takes 3 epochs with lr=3e-5; however, distillation takes 30~50 epochs with lr=1e-4. The conclusions are based on our experiments, and you are advised to try on your own data.
Q: My teacher model and student model take different inputs (they do not share vocabularies), so how can I distill?
A: You need to feed different batches to the teacher and the student. See the section Feed Different batches to Student and Teacher, Feed Cached Values in the full documentation.
Q: I have stored the logits from my teacher model. Can I use them in the distillation to save the forward pass time?
A: Yes, see the section Feed Different batches to Student and Teacher, Feed Cached Values in the full documentation.
Multi-GPU training support is only available throughDataParallel
currently.- Multi-label classification is not supported.
If you find TextBrewer is helpful, please cite our paper:
@InProceedings{textbrewer-acl2020-demo,
title = "{T}ext{B}rewer: {A}n {O}pen-{S}ource {K}nowledge {D}istillation {T}oolkit for {N}atural {L}anguage {P}rocessing",
author = "Yang, Ziqing and Cui, Yiming and Chen, Zhipeng and Che, Wanxiang and Liu, Ting and Wang, Shijin and Hu, Guoping",
booktitle = "Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics: System Demonstrations",
year = "2020",
publisher = "Association for Computational Linguistics",
url = "https://www.aclweb.org/anthology/2020.acl-demos.2",
pages = "9--16",
}
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