I didn't hear about "RealtimeKit" before, so maybe I missed some things.
My first impression is that it is not a solution.
* Why are cgroups not a good solution for that ? They can limit the share
of CPU time some threads get. I didn't understand what the problem is
* Why is a daemon called a "Kit" ? It seems nowadays every new thing is
some "FooKit", where each of those Kits replaces a well-known UNIX
mechanism with something undocumented nobody knows. It also seems that
everything which is called a "Kit" is kind-of implicitely accepted as the
new official standard way to do things.
* Where is the advantage of having a daemon which assigns RT priority to
processes if they ask for it over giving those processes the permission
to assign them RT priority themselves ? Isn't this just a big backdoor ?
Like a "friend" in a C++ class ? "I'm not allowed to do this, but I know
somebody who is, and he does everything for me I ask for" ?
* It is correct that SCHED_FIFO or SCHED_RR would be risky without
limitations. But this RealtimeKit looks like a big hack to get around
unsatisfying behaviour of the scheduler. There is a SCHED_EDF extension
to the normal Linux scheduler in development, where you can assign
periods and budgets to threads (which they cannot overrun). This looks to
me like a much better solution.