Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933400AbbLOM7H (ORCPT ); Tue, 15 Dec 2015 07:59:07 -0500 Received: from mail-lf0-f45.google.com ([209.85.215.45]:33524 "EHLO mail-lf0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932283AbbLOM7F (ORCPT ); Tue, 15 Dec 2015 07:59:05 -0500 MIME-Version: 1.0 In-Reply-To: <566FD446.1080004@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> From: Vincent Guittot Date: Tue, 15 Dec 2015 13:58:42 +0100 Message-ID: Subject: Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity To: Luca Abeni Cc: Peter Zijlstra , Steve Muckle , Ingo Molnar , linux-kernel , "linux-pm@vger.kernel.org" , Morten Rasmussen , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Michael Turquette Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2161 Lines: 59 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 Vincent > > > Luca > > >> >>> As done, for example, here: >>> https://github.com/lucabe72/linux-reclaiming/tree/track-utilisation-v2 >>> (in particular, see >>> >>> https://github.com/lucabe72/linux-reclaiming/commit/49fc786a1c453148625f064fa38ea538470df55b >>> ) >>> I understand this approach might look too complex... But I think it is >>> much less pessimistic while still being "safe". >>> If there is something that I can do to make that code more acceptable, >>> let me know. >>> >>> >>> 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/