The paper revisits the generation of interfaces for compositional real-time scheduling. Following an established line of research, we use periodic resource models in component interfaces to describe resource demand of the component. We identify a deficiency of existing interface generation algorithms that may require parameters of the resource model to be infeasibly small. We propose a new algorithm for interface generation that avoids this deficiency. We further demonstrate that resource utilization can be improved by using dual-periodic resource model (DPRM) interfaces that employ two periodic resource models to characterize the resource demand more precisely.