Solved by ptrblck in post #6 
              
              
                Sorry for the misleading message. 
The input will completely processed. Each group will see half the input channels, and producing half the output channels, and both subsequently concatenated (from the docs). 
This code demonstrates the behavior better: 
conv = nn.Conv2d(6, 6, 3, 1, 1, groups=2, bia…