A Callback which converts a fastai `Learner` and input to channels_last format.

Using Mixed Precision, image models trained in channels last format on Nvidia Tensor Cores can achieve 8%-35% increased performance over contiguous format.

Channels last memory format is only implemented for 4D NCHW Tensors. Not all PyTorch operators have been converted to support channels last. See (Beta) Channels Last Memory Format in PyTorch for more details.

Channels Last format can error out if torch.backends.cudnn.benchmark = False, e.g. via fast.ai's no_random context manager. If this occurs the less_random context manager instead. This will allow reproducable training on the same GPU, PyTorch, and CUDA setup at the expense of less reproducablity should any of those change.

class ChannelsLastTfm[source]

ChannelsLastTfm(enc=None, dec=None, split_idx=None, order=None) :: DisplayedTransform

Sets image-like inputs to channels_last format. For use in ChannelsLastCallback

Channels last format requires inputs to be 4D NCHW Tensors, so ChannelsLastTfm only encodes TensorImageBase and TensorMask inputs to channels last using fastcore's type dispatch.

To set another input type as channels last format, patch ChannelsLastTfm.encodes to dispatch for that type.

class ChannelsLastCallback[source]

ChannelsLastCallback() :: Callback

Channels last training using PyTorch's Channels Last Memory Format (beta)

Convenience Methods


Learner.to_channelslast(to_fp16=True, init_scale=65536.0, growth_factor=2.0, backoff_factor=0.5, growth_interval=2000, enabled=True)

Set Learner and inputs to channels_last format and Mixed Precision by default



Set Learner and inputs to contiguous_format (default format), optionally to single precision