as jiraya told him the purpose of the training was to control kurama's chakra,before starting to learn a new jutsu,and he was trying to do that,but was doing it the wrong way.
he was trying to take kurama's chakra for each time he wanted to use it he had to fight kurama's will who did not want to let go of his chakra,while the right way is to was the way he did it in the turtle island:beat the crap out of kurama,take his chakra,seal it away seperately from him.
he lost much of time in doing that,and reduced even his life span,but that made his body accustomed to kurama's chakra much more.
which what made him use kurama's chakra much easier once he got it and kurama no longer resisting him.