heavyfranz:

Somewhere I read that at least the scattering operation is done automatically segmenting the input tensor on the first axis, is it true?


Yes, this is truth. DataParallel will consider the first dimension as the batch dimension.

Finally, just to know, in your opinion, is the code is at least correct for the DataParallel construct?

It should work I think. But, usually the model is moved to the the target device before passing it to DataParallel ctor, like:
my = nn.DataParallel(model.to(device))