Participation in GSoC 2016

[Sebastian Huber]

On 18/03/16 14:38, Darshit Shah wrote:
> > "schedulable task sets would miss their deadlines since it does not 
> consider
> > migrating high priority tasks"
> >
> > I think this is not correct. The current APA scheduler should implement
> > strong APA. However, it may iterate several times over all (!) ready 
> tasks.
> > This is the actual problem.
> >
> I may be wrong, but I think the current implementation does indeed not 
> consider strong APA guarantees.
>
> The `_Scheduler_priority_affinity_SMP_Get_lowest_scheduled` method 
> tries to find a thread that needs to be migrated to another core in 
> order to schedule the selected thread. In this method, on line 274 is 
> the comment:
>
>       /*
>          * If we didn't find a thread which is of equal or lower
>     importance
>          * than filter thread is, then we can't schedule the filter thread
>          * to execute.
>          */
>
>
> If I understand this comment correctly, the scheduler does not 
> consider threads for migration if they are not of "equal or lower 
> importance" than the filter thread.

In contrast to the Linux push/pull scheduler you search here in the set 
of all scheduled/ready threads and not just in your local queue. I 
didn't look into the details, but I think this is enough for strong APA. 
See also _Scheduler_priority_affinity_SMP_Check_for_migrations().

-- 
Sebastian Huber, embedded brains GmbH

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