From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753773AbbLOMUU (ORCPT ); Tue, 15 Dec 2015 07:20:20 -0500 Received: from casper.infradead.org ([85.118.1.10]:39520 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752504AbbLOMUS (ORCPT ); Tue, 15 Dec 2015 07:20:18 -0500 Date: Tue, 15 Dec 2015 13:20:15 +0100 From: Peter Zijlstra To: Luca Abeni Cc: Vincent Guittot , Steve Muckle , Ingo Molnar , linux-kernel , "linux-pm@vger.kernel.org" , Morten Rasmussen , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Michael Turquette Subject: Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Message-ID: <20151215122015.GA6357@twins.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <566FD446.1080004@unitn.it> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.