BingBertSQuAD Fine-tuning

In this tutorial we will be adding DeepSpeed to the BingBert model for the SQuAD fine-tuning task, called “BingBertSquad” henceforth. We will also demonstrate performance gains.

Overview

If you don’t already have a copy of the DeepSpeed repository, please clone in now and checkout the DeepSpeedExamples submodule the contains the BingBertSquad example (DeepSpeedExamples/BingBertSquad) we will be going over in the rest of this tutorial.

git clone https://github.com/microsoft/DeepSpeed
cd DeepSpeed
git submodule update --init --recursive
cd DeepSpeedExamples/BingBertSquad

Pre-requisites

You also need a pre-trained BERT model checkpoint from either DeepSpeed, HuggingFace, or TensorFlow to run the fine-tuning. Regarding the DeepSpeed model, we will use checkpoint 160 from the BERT pre-training tutorial.

Running BingBertSquad

  • DeepSpeed-enabled: We provide a shell script that you can invoke to start training with DeepSpeed, it takes 4 arguments: bash run_squad_deepspeed.sh <NUM_GPUS> <PATH_TO_CHECKPOINT> <PATH_TO_DATA_DIR> <PATH_TO_OUTPUT_DIR>. The first argument is the number of GPUs to train with, second argument is the path to the pre-training checkpoint, third is the path to training and validation sets (e.g., train-v1.1.json), and fourth is path to an output folder where the results will be saved. This script will invoke nvidia_run_squad_deepspeed.py.
  • Unmodified baseline If you would like to run a non-DeepSpeed enabled version of fine-tuning we provide a shell script that takes the same arguments as the DeepSpeed one named run_squad_baseline.sh. This script will invoke nvidia_run_squad_baseline.py.

DeepSpeed Integration

The main part of training is done in nvidia_run_squad_deepspeed.py, which has already been modified to use DeepSpeed. The run_squad_deepspeed.sh script helps to invoke training and setup several different hyperparameters relevant to the training process. In the next few sections we will cover what changes we made to the baseline in order to enable DeepSpeed, you don’t have to make these changes yourself since we have already done them for you.

Configuration

The deepspeed_bsz24_config.json file gives the user the ability to specify DeepSpeed options in terms of batch size, micro batch size, learning rate, and other parameters. When running the nvidia_run_squad_deepspeed.py, in addition to the --deepspeed flag to enable DeepSpeed, the appropriate DeepSpeed configuration file must be specified using --deepspeed_config deepspeed_bsz24_config.json. Table 1 shows the fine-tuning configuration used in our experiments.

Parameters Value
Total batch size 24
Train micro batch size per GPU 3
Optimizer Adam
Learning rate 3e-5
Sequence-length 384
Weight-decay 0.0
Epoch count 2

Table 1. Fine-tuning configuration

Argument Parsing

The first step to apply DeepSpeed is adding arguments to BingBertSquad, using deepspeed.add_config_arguments() in the beginning of the main entry point as in the main() function in nvidia_run_squad_deepspeed.py. The argument passed to add_config_arguments() is obtained from the get_argument_parser() function in utils.py.

parser = get_argument_parser()
# Include DeepSpeed configuration arguments
parser = deepspeed.add_config_arguments(parser)
args = parser.parse_args()

Similar to this, all the options with their corresponding description are available in utils.py.

Training

Initialization

DeepSpeed has an initialization function to wrap the model, optimizer, LR scheduler, and data loader. For BingBertSquad, we simply augment the baseline script with the initialize function to wrap the model and create the optimizer as follows:

model, optimizer, _, _ = deepspeed.initialize(
    args=args,
    model=model,
    model_parameters=optimizer_grouped_parameters
)

Forward pass

This is identical in both Baseline and DeepSpeed, and is performed by loss = model(input_ids, segment_ids, input_mask, start_positions, end_positions).

Backward pass

In the Baseline script you need to handle the all-reduce operation at the gradient accumulation boundary explicitly by using enable_need_reduction() followed by optimizer.backward(loss) in FP16 and loss.backward() in FP32. In DeepSpeed, you may simply do model.backward(loss).

Weight updates

In the Baseline Script, you are required to explicitly specify the optimizer as FusedAdam (along with the handling of dynamic loss scaling) in FP16 and BertAdam in FP32, followed by the call optimizer.step() and optimizer.zero_grad(). DeepSpeed handles this internally (by setting the optimizer using the JSON config) when initialize() is called and thus you don’t need to explicitly write code but just do model.step().

Congratulations! Porting to DeepSpeed is complete.

Evaluation

Once training is complete, the EM and F1 scores may be obtained from the following command:

python evaluate-v1.1.py <PATH_TO_DATA_DIR>/dev-v1.1.json <PATH_TO_DATA_DIR>/predictions.json

Fine-tuning Results

The table summarizing the results are given below. In all cases (unless otherwise noted), the total batch size is set to 24 and training is conducted on 4 GPUs for 2 epochs on a DGX-2 node. A set of parameters (seeds and learning rates) were tried and the best ones were selected. All learning rates were 3e-5; We set the seeds to 9041 and 19068 for HuggingFace and TensorFlow models, respectively. The checkpoints used for each case are linked in the table below.

Case Model Precision EM F1
TensorFlow Bert-large-uncased-L-24_H-1024_A-16 FP16 84.13 91.03
HuggingFace Bert-large-uncased-whole-word-masking FP16 87.27 93.33

Enabling DeepSpeed’s Transformer Kernel for better Throughput

DeepSpeed’s optimized transformer kernel can be enabled during fine-tuning to increase the training throughput. In addition to supporting the models pre-trained with DeepSpeed, the kernel can be used with TensorFlow and HuggingFace checkpoints.

Enabling Transformer Kernel

An argument --deepspeed_transformer_kernel is already created in utils.py, we enable the transformer kernel by adding it in the shell script.

parser.add_argument(
    '--deepspeed_transformer_kernel',
    default=False,
    action='store_true',
    help='Use DeepSpeed transformer kernel to accelerate.'
)

In the BertEncoder class of the modeling source file, DeepSpeed transformer kernel is created as below when it is enabled by using --deepspeed_transformer_kernel argument.

if args.deepspeed_transformer_kernel:
    from deepspeed import DeepSpeedTransformerLayer, \
        DeepSpeedTransformerConfig, DeepSpeedConfig

    ds_config = DeepSpeedConfig(args.deepspeed_config)

    cuda_config = DeepSpeedTransformerConfig(
        batch_size=ds_config.train_micro_batch_size_per_gpu,
        max_seq_length=args.max_seq_length,
        hidden_size=config.hidden_size,
        heads=config.num_attention_heads,
        attn_dropout_ratio=config.attention_probs_dropout_prob,
        hidden_dropout_ratio=config.hidden_dropout_prob,
        num_hidden_layers=config.num_hidden_layers,
        initializer_range=config.initializer_range,
        seed=args.seed,
        fp16=ds_config.fp16_enabled
    )
    self.layer = nn.ModuleList([
        copy.deepcopy(DeepSpeedTransformerLayer(i, cuda_config))
        for i in range(config.num_hidden_layers)
    ])
else:
    layer = BertLayer(config)
    self.layer = nn.ModuleList([
        copy.deepcopy(layer)
        for _ in range(config.num_hidden_layers)
    ])

All configuration settings come from the DeepSpeed configuration file and command arguments and thus we must pass the args variable to here in this model.

Note: batch_size is the maximum bath size of input data, all fine-tuning training data or prediction data shouldn’t exceed this threshold, otherwise it will throw an exception. In the DeepSpeed configuration file micro batch size is defined as train_micro_batch_size_per_gpu, e.g., if it is set as 8 then the --predict_batch_size should also be 8.

For further details about the transformer kernel, please see our usage tutorial and technical deep dive on the fastest BERT training.

Loading HuggingFace and TensorFlow Pretrained Models

BingBertSquad supports both HuggingFace and TensorFlow pretrained models. Here, we show the two model examples:

  1. test/huggingface which includes the checkpoint Bert-large-uncased-whole-word-masking and bert json config.
  2. test/tensorflow which comes from a checkpoint zip from Google Bert-large-uncased-L-24_H-1024_A-16.
[test/huggingface]
bert-large-uncased-whole-word-masking-config.json
bert-large-uncased-whole-word-masking-pytorch_model.bin

[test/tensorflow]
bert_config.json
bert_model.ckpt.data-00000-of-00001
bert_model.ckpt.index
bert_model.ckpt.meta

There are three arguments used for loading these two types of checkpoints.

  1. --model_file, points to the pretrained model file.
  2. --ckpt_type, indicates the checkpoint type, TF for Tensorflow, HF for HuggingFace, default value is DS for DeepSpeed.
  3. --origin_bert_config_file, points to the BERT config file, usually saved in same folder of model_file.

We can add the following in our fine-tuning shell script in run_squad_deepspeed.sh to run the above HuggingFace and TensorFlow examples.

[HuggingFace]

--model_file test/huggingface/bert-large-uncased-whole-word-masking-pytorch_model.bin \
--ckpt_type HF \
--origin_bert_config_file test/huggingface/bert-large-uncased-whole-word-masking-config.json \

[TensorFlow]

--model_file /test/tensorflow/bert_model.ckpt \
--ckpt_type TF \
--origin_bert_config_file /test/tensorflow/bert_config.json \

Note:

  1. --deepspeed_transformer_kernel flag is required for using HuggingFace or TensorFlow pretrained models.

  2. --preln flag cannot be used with HuggingFace or TensorFlow pretrained models, since they use a post-layer-norm.

  3. BingBertSquad will check the pretrained models to have the same vocabulary size and won’t be able to run if there is any mismatch. We advise that you use a model checkpoint of the style described above or a DeepSpeed bing_bert checkpoint.

Tuning Performance

In order to perform fine-tuning, we set the total batch size to 24 as shown in Table 1. However, we can tune the micro-batch size per GPU to get high-performance training. In this regard, we have tried different micro-batch sizes on NVIDIA V100 using either 16GB or 32GB of memory. As Tables 2 and 3 show, we can improve performance by increasing the micro-batch. Compared with PyTorch, we can achieve up to 1.5x speedup for the 16GB V100 while supporting a 2x larger batch size per GPU. On the other hand, we can support as large as 32 batch size (2.6x higher than PyTorch) using a 32GB V100, while providing 1.3x speedup in the end-to-end fine-tune training. Note, that we use the best samples-per-second to compute speedup for the cases that PyTorch runs out-of-memory (OOM).

Micro batch size PyTorch DeepSpeed Speedup (x)
4 36.34 50.76 1.4
6 OOM 54.28 1.5
8 OOM 54.16 1.5

Table 2. Samples/second for running SQuAD fine-tuning on NVIDIA V100 (16GB) using PyTorch and DeepSpeed transformer kernels.

Micro batch size PyTorch DeepSpeed Speedup (x)
4 37.78 50.82 1.3
6 43.81 55.97 1.3
12 49.32 61.41 1.2
24 OOM 60.70 1.2
32 OOM 63.01 1.3

Table 3. Samples/second for running SQuAD fine-tuning on NVIDIA V100 (32GB) using PyTorch and DeepSpeed transformer kernels.

As mentioned, we can increase the micro-batch size per GPU from 3 to 24 or even higher if a larger batch size is desired. In order to support a larger micro-batch size, we may need to enable different memory-optimization flags for our transformer kernel as described in DeepSpeed Transformer Kernel tutorial. Table 4 shows which optimization flags are required for running different range of micro-batch sizes.

Micro batch size NVIDIA V100 (32-GB) NVIDIA V100 (16-GB)
> 4 - normalize_invertible
> 6 - attn_dropout_checkpoint, gelu_checkpoint
> 12 normalize_invertible, attn_dropout_checkpoint OOM
> 24 gelu_checkpoint OOM

Table 4. The setting of memory-optimization flags for a range of micro-batch size on 16-GB and 32-GB V100.

FineTuning model pre-trained with DeepSpeed Transformer Kernels

Fine-tuning the model pre-trained using DeepSpeed Transformer and the recipe in DeepSpeed Fast-Bert Training should yield F1 score of 90.5 and is expected to increase if you let the pre-training longer than suggested in the tutorial.

To get these results, we do require some tuning of the dropout settings as described below:

Dropout Setting

For the fine-tuning, we only use the deterministic transformer to have reproducible the fine-tuning results. But, we choose different values for dropout based on whether pre-training was done using deterministic or stochastic transformer (Please see Transformer tutorial for more detail of selecting these two modes).

For models pre-trained with deterministic transformer, we use the same dropout ratio used in pre-training (0.1). However, we slightly increase the dropout ratio when fine-tuning the model pre-trained using the stochastic transformer to compensate for the lack of stochastic noise during fine-tuning.

Pre-training mode Dropout ratio
Deterministic 0.1
Stochastic 0.12 - 0.14

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