Re: New PriorityInheritanceTest - bug in 2.6.17-rt7 confirmed

[Esben Nielsen]

On Thu, 6 Jul 2006, Ingo Molnar wrote:

> * Esben Nielsen <nielsen.esben@xxxxxxxxxxxxxx> 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.)
I think that is more or less what my patch does...

Esben

> 	Ingo
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