From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933628Ab0KOT0p (ORCPT ); Mon, 15 Nov 2010 14:26:45 -0500 Received: from mail2.unitn.it ([193.205.206.54]:52734 "EHLO mail2.unitn.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933169Ab0KOT0o (ORCPT ); Mon, 15 Nov 2010 14:26:44 -0500 Message-ID: <4CE18895.8060101@unitn.it> Date: Mon, 15 Nov 2010 20:23:01 +0100 From: Luca Abeni User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 MIME-Version: 1.0 To: "James H. Anderson" CC: Raistlin , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Steven Rostedt , Chris Friesen , oleg@redhat.com, Frederic Weisbecker , Darren Hart , Johan Eker , "p.faure" , linux-kernel , Claudio Scordino , michael trimarchi , Fabio Checconi , Tommaso Cucinotta , Juri Lelli , Nicola Manica , Dhaval Giani , Harald Gustafsson , paulmck , Bjoern Brandenburg Subject: Re: [RFC][PATCH 18/22] sched: add reclaiming logic to -deadline tasks References: <1289588215.6525.697.camel@Palantir> <80992760-24F2-42AE-AF2D-15727F6A1C81@email.unc.edu> <4CE17DD2.3060807@cs.unc.edu> In-Reply-To: <4CE17DD2.3060807@cs.unc.edu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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