Messages in this thread | | | Date | Mon, 15 Nov 2010 20:23:01 +0100 | From | Luca Abeni <> | Subject | Re: [RFC][PATCH 18/22] sched: add reclaiming logic to -deadline tasks |
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Hi James,
On 15/11/10 19:37, James H. Anderson wrote: [...] >>> The problem the stochastic execution time model tries to address is the >>> WCET computation mess, WCET computation is hard and often overly >>> pessimistic, resulting in under-utilized systems. >>> >> I know, and it's very reasonable. The point I'm trying to make is that >> resource reservation tries to address the very same issue. >> I am all but against this model, just want to be sure it's not too much >> in conflict to the other features we have, especially with resource >> reservation. Especially considering that --if I got the whole thing >> about this scheduler right-- resource reservation is something we really >> want, and I think UNC people would agree here, since I heard Bjorn >> stating this very clear both in Dresden and in Dublin. :-) >> >> BTW, I'm adding them to the Cc, seems fair, and more useful than all >> this speculation! :-P >> >> Bjorn, Jim, sorry for bothering. If you're interested, this is the very >> beginning of the whole thread: >> http://lkml.org/lkml/2010/10/29/67 [...] > If you're talking about our most recent "stochastic" paper, it is about > supporting > soft real-time task systems on a multiprocessor where resource > reservations are > used. The main result of the paper is that if you provision the > reservation for a > task slightly higher than it's average-case execution time, and if you > use a > scheduling algorithm (like global EDF) that ensures bounded tardiness > (w.r.t. > these reservations), then the task's expected tardiness will be bounded > and the > expected bound does not depend on worst-case execution times. I'm not > sure if > slack-reallocation methods have come up in this discussion (sorry, I'm > really > pressed for time and didn't look), but we didn't get into that in our > paper. So, if I understand well (sorry, I am just trying to make a short summary to check if we are aligned) your analysis is similar to the one presented in the papers I mentioned earlier in this thread (different stochastic modelling, but similar approach): you analyse a reservation in isolation and you provide some stochastic tardiness guarantees based on an (e_i, p_i) service model.... Right?
If my understanding is correct (please, correct me if I am wrong), your analysis can be applied even with the current version of Dario's patch (I mean: no modifications to the patch are needed for removing assumptions about WCET knowledge... Your paper uses a sporadic server for the reservation mechanism, but I think a CBS can work too...).
Thanks, Luca
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