Participation in GSoC 2016

[Darshit Shah]

Any further comments are appreciated.

On 18 March 2016 at 15:59, Darshit Shah <darnir at gmail.com> wrote:

>
>
> On 18 March 2016 at 14:48, Sebastian Huber <
> sebastian.huber at embedded-brains.de> wrote:
>
>>
>>
>> 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().
>>
>>
> That is true. Unlike the linux scheduler, all currently scheduled threads
> are considered for migration, but then it seems we only decide to migrate a
> thread if its priority is lower than the thread being dispatched. In case
> I'm wrong then the current implementation is indeed Strong APA, just with a
> bad time complexity. Else, we still have some form of a weak APA constrain
> in the scheduler.
>
>>
>> --
>> Sebastian Huber, embedded brains GmbH
>>
>> Address : Dornierstr. 4, D-82178 Puchheim, Germany
>> Phone   : +49 89 189 47 41-16
>> Fax     : +49 89 189 47 41-09
>> E-Mail  : sebastian.huber at embedded-brains.de
>> PGP     : Public key available on request.
>>
>> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
>>
>>
>
>
> --
> Thanking You,
> Darshit Shah
>
>


-- 
Thanking You,
Darshit Shah
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