Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754795AbdDMPQn (ORCPT ); Thu, 13 Apr 2017 11:16:43 -0400 Received: from mail-oi0-f52.google.com ([209.85.218.52]:33399 "EHLO mail-oi0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754263AbdDMPQl (ORCPT ); Thu, 13 Apr 2017 11:16:41 -0400 MIME-Version: 1.0 In-Reply-To: <20170413133928.jmykwcq4qq5grktk@hirez.programming.kicks-ass.net> References: <1491815909-13345-1-git-send-email-vincent.guittot@linaro.org> <20170410173802.orygigjbcpefqtdv@hirez.programming.kicks-ass.net> <20170411075221.GA30421@linaro.org> <20170413133928.jmykwcq4qq5grktk@hirez.programming.kicks-ass.net> From: Vincent Guittot Date: Thu, 13 Apr 2017 17:16:20 +0200 Message-ID: Subject: Re: [PATCH v2] sched/fair: update scale invariance of PELT To: Peter Zijlstra Cc: Ingo Molnar , linux-kernel , Dietmar Eggemann , Morten Rasmussen , Yuyang Du , Paul Turner , Ben Segall 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: 1679 Lines: 36 On 13 April 2017 at 15:39, Peter Zijlstra wrote: > On Tue, Apr 11, 2017 at 09:52:21AM +0200, Vincent Guittot wrote: > >> > Secondly, what's up with the util_sum < LOAD_AVG_MAX * 1000 thing? >> >> The lost idle time makes sense only if the task can also be "idle" >> when running at max capacity. When util_sum reaches the >> LOAD_AVG_MAX*SCHED_CAPACITY_SCALE value, all tasks are considered to >> be the same as we can't make any difference between a task running >> 400ms or a task running 400sec. It means that these tasks are "always >> running" tasks even at max capacity. In this case, there is no lost >> idle time as they always run and tracking and adding back the lost >> idle time because we run at lower capacity doesn't make sense anymore >> so we discard it. > > Right, this is the point we reached yesterday with the too low F. At > that point you cannot know and we assuming u=1, F<1 -> u=1, F=1, which > is a sensible assumption. > >> Then an always running task can have a util_sum that is less than the >> max value because of the rounding (util_avg varies between >> [1006..1023]), so I use LOAD_AVG_MAX*1000 instead of LOAD_AVG_MAX*1024 > > OK, so the reason util_avg varies is because we compute it wrong. And I > think we can easily fix that once we pull out all the factors (which > would mean your patch and the pulling out of weight patch which still > needs to be finished). That would be great to remove this unwanted variation. > > But you're comparing against util_sum here, that behaves slightly > different. I think you want 'util_sum >= 1024 * (LOAD_AVG_MAX - 1024)' > instead. yes, the variation happens on the util_sum