Re: New PriorityInheritanceTest - bug in 2.6.17-rt7 confirmed

[Esben Nielsen <nielsen.esben@googlemail.com>]

On Thu, 6 Jul 2006, Ingo Molnar wrote:

>
> * 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.)
>
I think that is more or less what my patch does...

Esben

> 	Ingo
>