EDF Pluggable Scheduler

Petr Benes benesp16 at fel.cvut.cz
Mon Apr 4 17:14:56 UTC 2011


Thank you for the reply, it looks that for the best convenience matching 
to the current pluggable scheduler framework your advice regarding the 
Scheduler_Update is reasonable and instinctive.

However, I have just one more question. If we consider deadlines as 
current_priority, which is an uint32 type, since the deadline is a 
continuously increasing time, the current_priority overflows sooner or 
later. That is not a problem for the deadline comparison, I can handle 
it, but starts to matter as far as the Priority Inheritance Protocol is 
concerned. It does not know that a later deadline may be represented by 
a lower (overflown) number.

How do you look upon this issue? Would be a solution to have another 
pluggable function implementing a priority comparison operation? Is this 
just a short-sighted point of view of EDF?

Kind regards


On 03/31/2011 09:15 PM, Gedare Bloom wrote:
> Hi Petr,
> This is an interesting project. I did not concern myself with
> synchronization issues, so I did not implement anything to deal with
> deadilne interchange. With the pluggable scheduler framework, it
> should be sufficient to implement Scheduler_Update -- I don't know if
> enough information is passed currently, you may need to ensure that
> current_priority always represents the thread's deadline.
> I consider this a failing of the tight integration of threads and
> priority values. I tried to refactor this priority handling into a
> separate Priority Handler, but it was hard to separate the priority
> logic and still have efficient thread management.  It might be
> worthwhile to reconsider this in light of the need to handle priority
> in an opaque way in the mutex code.
> There was another edf implementation done (
> http://code.google.com/p/rtems-edf/ ) that is based on Martin's work
> as well. It was implemented before the pluggable interface.
> I have not revised my EDF to fit the current pluggable framework (it
> is close, but some variations), as I am waiting on the merge of the
> red-black tree (https://www.rtems.org/bugzilla/show_bug.cgi?id=1641).
> Good luck, and feel free to contact me for more details/assistance.
> Gedare
> On Thu, Mar 31, 2011 at 6:59 AM, Petr Benes<benesp16 at fel.cvut.cz>  wrote:
>> Dear Mr. Bloom,
>> I am applying to you for an advice regarding RTEMS scheduling.
>> I am currently working on my master thesis at CTU Prague dealing with
>> porting a resource reservation framework (www.frescor.org) onto RTEMS. I
>> need to ensure a temporal independence/isolation of separate tasks and for
>> this we are to use an EDF scheduler with an incorporated CBS (Constant
>> Bandwidth Server).
>> As far as I am concerned, you work on some EDF or you have it done. I assume
>> it is a pluggable one, since there is the feature in RTEMS 4.11 already
>> implemented.
>> I have just finished a quickie implementation of a pluggable EDF on my own
>> (git at rtime.felk.cvut.cz:/rtems-pluggable-edf) having Martin Molnar's one as
>> an example. I guess you know each other (he is also from CTU).
>> The question I have is whether you happen to have some solution or at least
>> an idea how to handle Deadline interchange and you are willing to share the
>> experience. There is nothing reasonable proposed in the thesis by Martin
>> Molnar (https://dip.felk.cvut.cz/browse/pdfcache/molnam1_2006dipl.pdf). So
>> far, for sake of simplicity, I was thinking about some kind of hack making
>> use of the current RAPs used by priority scheduling.
>> Best regards
>> Bc. Petr Beneš
>> --------------------------
>> mail  : benesp16 at fel.cvut.cz
>> web   : www.petben.net
>> mobile: +420 774 990 750
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Bc. Petr Beneš
mail  : benesp16 at fel.cvut.cz
web   : www.petben.net
mobile: +420 774 990 750
icq   : 286131561

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