Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754040AbbLONl7 (ORCPT ); Tue, 15 Dec 2015 08:41:59 -0500 Received: from mail-wm0-f42.google.com ([74.125.82.42]:36705 "EHLO mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753992AbbLONl4 (ORCPT ); Tue, 15 Dec 2015 08:41:56 -0500 Subject: Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity To: Vincent Guittot References: <1449641971-20827-1-git-send-email-smuckle@linaro.org> <1449641971-20827-10-git-send-email-smuckle@linaro.org> <20151214151729.GQ6357@twins.programming.kicks-ass.net> <20151214221231.39b5bc4e@luca-1225C> <566FD446.1080004@unitn.it> Cc: Peter Zijlstra , Steve Muckle , Ingo Molnar , linux-kernel , "linux-pm@vger.kernel.org" , Morten Rasmussen , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Michael Turquette From: Luca Abeni Message-ID: <567018A1.1010208@unitn.it> Date: Tue, 15 Dec 2015 14:41:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux i686; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1793 Lines: 43 On 12/15/2015 01:58 PM, Vincent Guittot wrote: > On 15 December 2015 at 09:50, Luca Abeni wrote: >> On 12/15/2015 05:59 AM, Vincent Guittot wrote: >> [...] >>>>>> >>>>>> So I don't think this is right. AFAICT this projects the WCET as the >>>>>> amount of time actually used by DL. This will, under many >>>>>> circumstances, vastly overestimate the amount of time actually >>>>>> spend on it. Therefore unduly pessimisme the fair capacity of this >>>>>> CPU. >>>>> >>>>> > > [snip] > >>> The 2nd definition is used to compute the remaining capacity for the >>> CFS scheduler. This one doesn't need to be updated at each wake/sleep >>> of a deadline task but should reflect the capacity used by deadline in >>> a larger time scale. The latter will be used by the CFS scheduler at >>> the periodic load balance pace >> >> Ok, so as I wrote above this really looks like an average utilisation. >> My impression (but I do not know the CFS code too much) is that the mainline >> kernel is currently doing the right thing to compute it, so maybe there is >> no >> need to change the current code in this regard. >> If the current code is not acceptable for some reason, an alternative would >> be to measure the active utilisation for frequency scaling, and then apply a >> low-pass filter to it for CFS. > > In this case, it's probably easier to split what is already done into > a rt_avg metric and a dl_avg metric Yes, I think this could be the best approach for what concerns the average utilisation used by CFS. Luca -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/