We seem to be getting off the topic here. The point is that Linux is used in real-time applications - I have worked on several myself. Real time is about determinism and deadlines, and typically there are a range of acceptable behaviours. Dead line scheduling is a valuable tool in designing systems that have to meet deadlines (in essence, it makes the analysis easier). So, it would make sense to have such a scheduler as an option in the Linux. People seem to be arguing against improving the kernel, and I don't understand why.