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Summary: Pull Request resolved: https://github.com/pytorch/fairseq/pull/2492 Reviewed By: ngoyal2707 Differential Revision: D23177728 Pulled By: myleott fbshipit-source-id: 32424f61cab57f759f87e16e8d5144d3eed5ae36
207 lines
8.1 KiB
ReStructuredText
207 lines
8.1 KiB
ReStructuredText
Evaluating Pre-trained Models
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=============================
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First, download a pre-trained model along with its vocabularies:
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.. code-block:: console
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> curl https://dl.fbaipublicfiles.com/fairseq/models/wmt14.v2.en-fr.fconv-py.tar.bz2 | tar xvjf -
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This model uses a `Byte Pair Encoding (BPE)
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vocabulary <https://arxiv.org/abs/1508.07909>`__, so we'll have to apply
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the encoding to the source text before it can be translated. This can be
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done with the
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`apply\_bpe.py <https://github.com/rsennrich/subword-nmt/blob/master/subword_nmt/apply_bpe.py>`__
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script using the ``wmt14.en-fr.fconv-cuda/bpecodes`` file. ``@@`` is
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used as a continuation marker and the original text can be easily
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recovered with e.g. ``sed s/@@ //g`` or by passing the ``--remove-bpe``
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flag to :ref:`fairseq-generate`. Prior to BPE, input text needs to be tokenized
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using ``tokenizer.perl`` from
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`mosesdecoder <https://github.com/moses-smt/mosesdecoder>`__.
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Let's use :ref:`fairseq-interactive` to generate translations interactively.
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Here, we use a beam size of 5 and preprocess the input with the Moses
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tokenizer and the given Byte-Pair Encoding vocabulary. It will automatically
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remove the BPE continuation markers and detokenize the output.
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.. code-block:: console
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> MODEL_DIR=wmt14.en-fr.fconv-py
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> fairseq-interactive \
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--path $MODEL_DIR/model.pt $MODEL_DIR \
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--beam 5 --source-lang en --target-lang fr \
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--tokenizer moses \
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--bpe subword_nmt --bpe-codes $MODEL_DIR/bpecodes
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| loading model(s) from wmt14.en-fr.fconv-py/model.pt
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| [en] dictionary: 44206 types
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| [fr] dictionary: 44463 types
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| Type the input sentence and press return:
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Why is it rare to discover new marine mammal species?
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S-0 Why is it rare to discover new marine mam@@ mal species ?
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H-0 -0.0643349438905716 Pourquoi est-il rare de découvrir de nouvelles espèces de mammifères marins?
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P-0 -0.0763 -0.1849 -0.0956 -0.0946 -0.0735 -0.1150 -0.1301 -0.0042 -0.0321 -0.0171 -0.0052 -0.0062 -0.0015
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This generation script produces three types of outputs: a line prefixed
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with *O* is a copy of the original source sentence; *H* is the
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hypothesis along with an average log-likelihood; and *P* is the
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positional score per token position, including the
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end-of-sentence marker which is omitted from the text.
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Other types of output lines you might see are *D*, the detokenized hypothesis,
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*T*, the reference target, *A*, alignment info, *E* the history of generation steps.
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See the `README <https://github.com/pytorch/fairseq#pre-trained-models>`__ for a
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full list of pre-trained models available.
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Training a New Model
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====================
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The following tutorial is for machine translation. For an example of how
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to use Fairseq for other tasks, such as :ref:`language modeling`, please see the
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``examples/`` directory.
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Data Pre-processing
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-------------------
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Fairseq contains example pre-processing scripts for several translation
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datasets: IWSLT 2014 (German-English), WMT 2014 (English-French) and WMT
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2014 (English-German). To pre-process and binarize the IWSLT dataset:
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.. code-block:: console
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> cd examples/translation/
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> bash prepare-iwslt14.sh
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> cd ../..
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> TEXT=examples/translation/iwslt14.tokenized.de-en
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> fairseq-preprocess --source-lang de --target-lang en \
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--trainpref $TEXT/train --validpref $TEXT/valid --testpref $TEXT/test \
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--destdir data-bin/iwslt14.tokenized.de-en
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This will write binarized data that can be used for model training to
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``data-bin/iwslt14.tokenized.de-en``.
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Training
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--------
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Use :ref:`fairseq-train` to train a new model. Here a few example settings that work
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well for the IWSLT 2014 dataset:
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.. code-block:: console
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> mkdir -p checkpoints/fconv
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> CUDA_VISIBLE_DEVICES=0 fairseq-train data-bin/iwslt14.tokenized.de-en \
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--lr 0.25 --clip-norm 0.1 --dropout 0.2 --max-tokens 4000 \
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--arch fconv_iwslt_de_en --save-dir checkpoints/fconv
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By default, :ref:`fairseq-train` will use all available GPUs on your machine. Use the
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``CUDA_VISIBLE_DEVICES`` environment variable to select specific GPUs and/or to
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change the number of GPU devices that will be used.
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Also note that the batch size is specified in terms of the maximum
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number of tokens per batch (``--max-tokens``). You may need to use a
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smaller value depending on the available GPU memory on your system.
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Generation
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----------
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Once your model is trained, you can generate translations using
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:ref:`fairseq-generate` **(for binarized data)** or
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:ref:`fairseq-interactive` **(for raw text)**:
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.. code-block:: console
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> fairseq-generate data-bin/iwslt14.tokenized.de-en \
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--path checkpoints/fconv/checkpoint_best.pt \
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--batch-size 128 --beam 5
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| [de] dictionary: 35475 types
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| [en] dictionary: 24739 types
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| data-bin/iwslt14.tokenized.de-en test 6750 examples
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| model fconv
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| loaded checkpoint trainings/fconv/checkpoint_best.pt
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S-721 danke .
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T-721 thank you .
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...
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To generate translations with only a CPU, use the ``--cpu`` flag. BPE
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continuation markers can be removed with the ``--remove-bpe`` flag.
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Advanced Training Options
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=========================
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Large mini-batch training with delayed updates
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----------------------------------------------
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The ``--update-freq`` option can be used to accumulate gradients from
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multiple mini-batches and delay updating, creating a larger effective
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batch size. Delayed updates can also improve training speed by reducing
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inter-GPU communication costs and by saving idle time caused by variance
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in workload across GPUs. See `Ott et al.
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(2018) <https://arxiv.org/abs/1806.00187>`__ for more details.
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To train on a single GPU with an effective batch size that is equivalent
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to training on 8 GPUs:
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.. code-block:: console
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> CUDA_VISIBLE_DEVICES=0 fairseq-train --update-freq 8 (...)
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Training with half precision floating point (FP16)
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--------------------------------------------------
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.. note::
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FP16 training requires a Volta GPU and CUDA 9.1 or greater
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Recent GPUs enable efficient half precision floating point computation,
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e.g., using `Nvidia Tensor Cores
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<https://docs.nvidia.com/deeplearning/sdk/mixed-precision-training/index.html>`__.
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Fairseq supports FP16 training with the ``--fp16`` flag:
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.. code-block:: console
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> fairseq-train --fp16 (...)
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Distributed training
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--------------------
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Distributed training in fairseq is implemented on top of ``torch.distributed``.
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The easiest way to launch jobs is with the `torch.distributed.launch
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<https://pytorch.org/docs/stable/distributed.html#launch-utility>`__ tool.
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For example, to train a large English-German Transformer model on 2 nodes each
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with 8 GPUs (in total 16 GPUs), run the following command on each node,
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replacing ``node_rank=0`` with ``node_rank=1`` on the second node:
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.. code-block:: console
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> python -m torch.distributed.launch --nproc_per_node=8 \
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--nnodes=2 --node_rank=0 --master_addr="192.168.1.1" \
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--master_port=1234 \
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$(which fairseq-train) data-bin/wmt16_en_de_bpe32k \
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--arch transformer_vaswani_wmt_en_de_big --share-all-embeddings \
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--optimizer adam --adam-betas '(0.9, 0.98)' --clip-norm 0.0 \
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--lr-scheduler inverse_sqrt --warmup-init-lr 1e-07 --warmup-updates 4000 \
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--lr 0.0005 --min-lr 1e-09 \
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--dropout 0.3 --weight-decay 0.0 --criterion label_smoothed_cross_entropy --label-smoothing 0.1 \
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--max-tokens 3584 \
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--fp16 --distributed-no-spawn
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Sharding very large datasets
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----------------------------
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It can be challenging to train over very large datasets, particularly if your
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machine does not have much system RAM. Most tasks in fairseq support training
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over "sharded" datasets, in which the original dataset has been preprocessed
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into non-overlapping chunks (or "shards").
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For example, instead of preprocessing all your data into a single "data-bin"
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directory, you can split the data and create "data-bin1", "data-bin2", etc.
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Then you can adapt your training command like so:
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.. code-block:: console
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> fairseq-train data-bin1:data-bin2:data-bin3 (...)
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Training will now iterate over each shard, one by one, with each shard
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corresponding to an "epoch", thus reducing system memory usage.
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