The realtime scheduler classes are intended to allow a developer to state
which tasks have the highest priorities with the assurance that, at any
given time, the highest-priority task will have unimpeded access to the
CPU. The kernel itself carries out a number of tasks that have tight time
constraints, so it is natural to want to assign realtime priorities to
kernel threads carrying out those tasks. But, as Peter Zijlstra argues
in a new patch set, it makes little sense for the kernel to be assigning
such priorities; to put an end to that practice, he is proposing to take
away most of the kernel’s ability to prioritize its own threads.

Source: LWN.net – [$] Controlling realtime priorities in kernel threads