message: add more comments for depthwise conv output format.
diff: @@ -497,6 +497,16 @@ class MklConvCustomBackpropFilterOp
  diff_filter_mkl_shape);
  } else {
  // Depthwise Conv2d: bwd_output_dims is GOIHW format
  + // | TensorFlow | MKLDNN
  + // ----------------------------------------------------------------
  + // filter_out_depth | depth_multiplier | depth_multiplier *
  + // | | group_count
  + // ----------------------------------------------------------------
  + // filter_in_depth | in_depth | in_depth / group_count
  + // For depthwise convolution, we have group_count == in_depth.
  + // So here G = original I, and I = 1.
  + // And the GOIHW is mkldnn format, here is try to extract the TF
  + // format, TF format is HWIO, as G = original I, so here is HWGO.
  TensorShape diff_filter_tf_shape(
  {bwd_output_dims[MklDnnFilterGroupDims::MKL_GROUP_FILTER_DIM_H],
  bwd_output_dims[MklDnnFilterGroupDims::MKL_GROUP_FILTER_DIM_W],
  