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.. testsetup:: *

    from pytorch_lightning.trainer.trainer import Trainer

16-bit training

Lightning offers 16-bit training for CPUs, GPUs and TPUs.

GPU 16-bit

16 bit precision can cut your memory footprint by half. If using volta architecture GPUs it can give a dramatic training speed-up as well.

Note

PyTorch 1.6+ is recommended for 16-bit

Native torch

When using PyTorch 1.6+ Lightning uses the native amp implementation to support 16-bit.

.. testcode::
    :skipif: not APEX_AVAILABLE and not NATIVE_AMP_AVALAIBLE

    # turn on 16-bit
    trainer = Trainer(precision=16)

Apex 16-bit

If you are using an earlier version of PyTorch Lightning uses Apex to support 16-bit.

Follow these instructions to install Apex. To use 16-bit precision, do two things:

  1. Install Apex
  2. Set the "precision" trainer flag.
$ git clone https://github.com/NVIDIA/apex
$ cd apex

# ------------------------
# OPTIONAL: on your cluster you might need to load cuda 10 or 9
# depending on how you installed PyTorch

# see available modules
module avail

# load correct cuda before install
module load cuda-10.0
# ------------------------

# make sure you've loaded a cuda version > 4.0 and < 7.0
module load gcc-6.1.0

$ pip install -v --no-cache-dir --global-option="--cpp_ext" --global-option="--cuda_ext" ./

Warning

NVIDIA Apex and DDP have instability problems. We recommend native 16-bit in PyTorch 1.6+

Enable 16-bit

.. testcode::
    :skipif: not APEX_AVAILABLE and not NATIVE_AMP_AVALAIBLE

    # turn on 16-bit
    trainer = Trainer(amp_level='O2', precision=16)

If you need to configure the apex init for your particular use case or want to use a different way of doing 16-bit training, override :meth:`pytorch_lightning.core.LightningModule.configure_apex`.

TPU 16-bit

16-bit on TPus is much simpler. To use 16-bit with TPUs set precision to 16 when using the tpu flag

.. testcode::
    :skipif: not XLA_AVAILABLE

    # DEFAULT
    trainer = Trainer(tpu_cores=8, precision=32)

    # turn on 16-bit
    trainer = Trainer(tpu_cores=8, precision=16)