torch.nn.SyncBatchNorm(num_features, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True, process_group=None)[source]
Applies Batch Normalization over a N-Dimensional input (a mini-batch of [N-2]D inputs with additional channel dimension) as described in the paper Batch Normalization: Accelerating Deep Network Training by Reducing Internal Covariate Shift.
The mean and standard-deviation are calculated per-dimension over all mini-batches of the same process groups.
and
are learnable parameter vectors of size C (where C is the input size). By default, the elements of
are sampled from
and the elements of
are set to 0.
Also by default, during training this layer keeps running estimates of its computed mean and variance, which are then used for normalization during evaluation. The running estimates are kept with a default momentum of 0.1.
If track_running_stats is set to False, this layer then does not keep running estimates, and batch statistics are instead used during evaluation time as well.
Note
This momentum argument is different from one used in optimizer classes and the conventional notion of momentum. Mathematically, the update rule for running statistics here is
, where
is the estimated statistic and
is the new observed value.
Because the Batch Normalization is done over the C dimension, computing statistics on (N, ) slices, it’s common terminology to call this Volumetric Batch Normalization or Spatio-temporal Batch Normalization.
Currently SyncBatchNorm only supports DistributedDataParallel with single GPU per process. Use torch.nn.SyncBatchNorm.convert_sync_batchnorm() to convert BatchNorm layer to SyncBatchNorm before wrapping Network with DDP.
Parameters：
- num_features – CCC from an expected input of size (N,C, )
- eps – a value added to the denominator for numerical stability. Default: 1e-5
- momentum – the value used for the running_mean and running_var computation. Can be set to
Nonefor cumulative moving average (i.e. simple average). Default: 0.1 - affine – a boolean value that when set to
True, this module has learnable affine parameters. Default:True - track_running_stats – a boolean value that when set to
True, this module tracks the running mean and variance, and when set toFalse, this module does not track such statistics and always uses batch statistics in both training and eval modes. Default:True - process_group – synchronization of stats happen within each process group individually. Default behavior is synchronization across the whole world
Shape：
- Input: (N,C, )(N, C, )(N,C, )
- Output: (N,C, )(N, C, )(N,C, ) (same shape as input)
Examples：
代码语言：javascript复制>>> # With Learnable Parameters
>>> m = nn.SyncBatchNorm(100)
>>> # creating process group (optional)
>>> # process_ids is a list of int identifying rank ids.
>>> process_group = torch.distributed.new_group(process_ids)
>>> # Without Learnable Parameters
>>> m = nn.BatchNorm3d(100, affine=False, process_group=process_group)
>>> input = torch.randn(20, 100, 35, 45, 10)
>>> output = m(input)
>>> # network is nn.BatchNorm layer
>>> sync_bn_network = nn.SyncBatchNorm.convert_sync_batchnorm(network, process_group)
>>> # only single gpu per process is currently supported
>>> ddp_sync_bn_network = torch.nn.parallel.DistributedDataParallel(
>>> sync_bn_network,
>>> device_ids=[args.local_rank],
>>> output_device=args.local_rank)classmethod
convert_sync_batchnorm(module, process_group=None)[source]
Helper function to convert torch.nn.BatchNormND layer in the model to torch.nn.SyncBatchNorm layer.
Parameters：
- module (nn.Module) – containing module
- process_group (optional) – process group to scope synchronization,
default is the whole world.
Returns：
- The original module with the converted torch.nn.SyncBatchNorm layer.
Example：
代码语言：javascript复制>>> # Network with nn.BatchNorm layer
>>> module = torch.nn.Sequential(
>>> torch.nn.Linear(20, 100),
>>> torch.nn.BatchNorm1d(100)
>>> ).cuda()
>>> # creating process group (optional)
>>> # process_ids is a list of int identifying rank ids.
>>> process_group = torch.distributed.new_group(process_ids)
>>> sync_bn_module = convert_sync_batchnorm(module, process_group)
