Re: New PriorityInheritanceTest - bug in 2.6.17-rt7 confirmed

[Ingo Molnar <mingo@elte.hu>]

* Esben Nielsen <nielsen.esben@googlemail.com> wrote:

> It can run within try_to_wake_up(). But then it the whole lock chain 
> is traversed in an atomic section. That unpredictable overall system 
> latencies since the locks can be in userspace. So it has to run in 
> some task. That task has to be high priority enough to preempt the 
> boosted tasks, but it can't be so high priority that it bothers any 
> higher priority threads than those involved in this. So it can't be, 
> forinstance a general priority 99 task we just use for this. We thus 
> need something running at a slightly higher priority than the priority 
> to which the tasks are boosted, but not a full +1 priority. I.e. we 
> need to run it at priority "+0.5".

we could just queue the task in front of the other task in the runqueue, 
and mark that task for reschedule if it's running currently. (Doing this 
is not without precedent: we do something similar in wake_up_new_task() 
to implement child-runs-first logic.)

	Ingo