Despite a blistering stoppage time free-kick from Martin Woods, Swansea were always in control and moved up to seventh in the table.
The future does not look as bright for Rotherham, who are now winless in 14 games and appear cast adrift at the foot of the table.
"It was a pretty poor performance, wcannot go on conceding goals," admitted Knill."The first was a free header and then we gave them a second.
"Whave got to try to be positive and stick together. We are going through a tough time - everyone can see that."