From mboxrd@z Thu Jan 1 00:00:00 1970 From: Luca Abeni Subject: Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Date: Tue, 15 Dec 2015 14:18:11 +0100 Message-ID: <56701313.8000800@unitn.it> 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> <20151215122015.GA6357@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wm0-f49.google.com ([74.125.82.49]:35337 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753405AbbLONSO (ORCPT ); Tue, 15 Dec 2015 08:18:14 -0500 Received: by mail-wm0-f49.google.com with SMTP id p66so90450399wmp.0 for ; Tue, 15 Dec 2015 05:18:13 -0800 (PST) In-Reply-To: <20151215122015.GA6357@twins.programming.kicks-ass.net> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Peter Zijlstra Cc: Vincent Guittot , Steve Muckle , Ingo Molnar , linux-kernel , "linux-pm@vger.kernel.org" , Morten Rasmussen , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Michael Turquette On 12/15/2015 01:20 PM, Peter Zijlstra wrote: > On Tue, Dec 15, 2015 at 09:50:14AM +0100, Luca Abeni wrote: >> On 12/15/2015 05:59 AM, Vincent Guittot wrote: > >>> 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. > > So CFS really only needs a 'vague' average idea on how much time it will > not get. Its best effort etc., so being a little wrong isn't a problem. > > The current code suffices, but I think the reason its been changed in > this series is that they want/need separate tracking for fifo/rr and > deadline in the next patch, and taking out deadline like proposed was > the easiest way of achieving that. Ah, ok. Thanks for explaining. So, I agree that this patch is not a good idea for estimating the average utilisation needed by CFS. Luca