Participation in GSoC 2016

Darshit Shah darnir at
Sun Mar 13 11:02:35 UTC 2016

On 03/10, Gedare Bloom wrote:
>Joel might answer about the state of the scheduling simulator.
@Joel, any thoughts / inputs on the state of the scheduling simulator 
would be very helpful. I'm currently trying to come up with a draft 
timeline for review, but this is a blocking factor. I've cloned the 
rtems-schedsim repository, but need some help / information on using it 
and what will need to be extended.
>I believe you eventually have to copy-paste your application into a
>form, so it is better if you stick to plain text. I don't even know if
>you can put images in. You may optionally link to a generated PDF,
>On Thu, Mar 10, 2016 at 6:13 AM, Darshit Shah <darnir at> wrote:
>> Hi,
>> I've been a little busy with my semester end exams and other things
>> recently. But I have spent time looking into the RTEMS Priority Scheduler
>> with Processor Affinities and the paper mentioned in the trac ticket.
>> At this point, I have a decent understanding of the paper and its algorithm
>> and am looking into how we may implement it in RTEMS. To this end, I am
>> looking for help / guidance.
>>> This would be a good project. I would add a few steps to simply
>>> implementing
>>> it.
>>> + Update the scheduling simulator since it is a lot easier to test using
>>> that.
>>>   It is also easier to ensure you keep the same behavior.
>> This sounds like it would be in important part of the implementation of the
>> paper. However, I do not know anything about the existing scheduling
>> simulator. Any links to this and basic pointers on how I should go about
>> extending it would be a great start. I'll incorporate this into my draft
>> proposal as soon as I have a better idea of what needs to be done.
>>> + Propose criteria for knowing if the new algorithm is really better for
>>>   RTEMS than the old one. Evaluating algorithms for RTEMS use involves
>>>   big-O of the algorithm, data space requirements (and big-O of that),
>>>   global knowledge required, and maybe other factors.
>> The new algorithm is almost definitely worse in time and space than the
>> existing algorithm. Based on a preliminary analysis, it will be able to use
>> the existing Priority Affinity Scheduler for the most part and add a O(|E|)
>> complexity to each thread blocking and unblocking operation.  Here, E is the
>> set of all processor affinity assignments, so it will approximately add an
>> extra linear increase in scheduling overhead w.r.t.  the number of processes
>> that use this scheduler.
>> I haven't specifically looked into the space requirements, but it will be
>> worse than the existing scheduler.
>> However, the point to realize is that after these changes, more user
>> programs that set processor affinities will be able to meet their deadlines
>> as compared to the existing scheduler. This should happen despite the higher
>> scheduling overheads.
>>> + Testing on scheduling simulator and in RTEMS testsuite to ensure
>>>   it is functionally identical to the current algorithm.
>> Once again, some pointers tot he scheduling simulator would help me a lot.
>>> If the algorithm is functionally identical to the current one and superior
>>> in execution time/data requirements, then replacing it is a no brainer.
>>> If there are trade-offs on when one is better than the other in real life,
>>> then we will all have to characterize those.
>> I was thinking more along the lines of writing a new scheduler instead of
>> replacing the existing one. A PriorityStringAPA scheduler that pretty much
>> reuses all the existing priority affinity scheduler code apart from the two
>> operations. This is because, with some task sets where the affinity
>> assignments are not too restrictive, the lower overheads of the existing
>> scheduler may be preferred over the new one.
>> I have also been writing my draft proposal for GSoC. A version is currently
>> available on GDrive and a link has been put on on the student tracking page.
>> However, I wanted to ask if sharing a PDF of the proposal would be possible.
>> Since, I would be more comfortable in making the entire proposal in Latex
>> and sharing the final PDF. If not, I can keep working on the proposal in
>> Google Docs.
>> --
>> Thanking You,
>> Darshit Shah

Thanking You,
Darshit Shah
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