docs(syncbn): complete syncbn document

GitOrigin-RevId: 9b8d546f0b1431d502ee6f69fd3ccbd072a73e71

imperative/python/megengine/functional/nn.py

@@ -1125,6 +1125,10 @@ def sync_batch_norm(
         Default: 0.9
     :param eps: a value added to the denominator for numerical stability.
         Default: 1e-5
+    :param eps_mode: mode of calculation for eps, "max" or "additive".
+        Default: "additive"
+    :param group: communication group, caculate mean and variance between this group.
+        Default: :obj:`~megengine.distributed.WORLD`
     :return: output tensor.
     """
     assert eps_mode.lower() in {"max", "additive"}, "unknown eps_mode: {}".format(

imperative/python/megengine/module/batchnorm.py

@@ -141,6 +141,35 @@ class _BatchNorm(Module):
 class SyncBatchNorm(_BatchNorm):
     r"""
     Applies Synchronized Batch Normalization for distributed training.
+
+    :type num_features: int
+    :param num_features: usually :math:`C` from an input of shape
+        :math:`(N, C, H, W)` or the highest ranked dimension of an input
+        less than 4D.
+    :type eps: float
+    :param eps: a value added to the denominator for numerical stability.
+        Default: 1e-5
+    :type momentum: float
+    :param momentum: the value used for the ``running_mean`` and ``running_var`` computation.
+        Default: 0.9
+    :type affine: bool
+    :param affine: a boolean value that when set to True, this module has
+        learnable affine parameters. Default: True
+    :type track_running_stats: bool
+    :param track_running_stats: when set to True, this module tracks the
+        running mean and variance. When set to False, this module does not
+        track such statistics and always uses batch statistics in both training
+        and eval modes. Default: True
+    :type freeze: bool
+    :param freeze: when set to True, this module does not update the
+        running mean and variance, and uses the running mean and variance instead of
+        the batch mean and batch variance to normalize the input. The parameter takes effect
+        only when the module is initilized with track_running_stats as True.
+        Default: False
+    :type group: :class:`~megengine.distributed.Group`
+    :param group: communication group, caculate mean and variance between this group.
+        Default: :obj:`~megengine.distributed.WORLD`
+    :return: output tensor.
     """
 
     def __init__(