Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964954AbcJQWwz (ORCPT ); Mon, 17 Oct 2016 18:52:55 -0400 Received: from foss.arm.com ([217.140.101.70]:45526 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933422AbcJQWwy (ORCPT ); Mon, 17 Oct 2016 18:52:54 -0400 Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes To: Vincent Guittot , Peter Zijlstra References: <57FFADC8.2020602@canonical.com> <43c59cba-2044-1de2-0f78-8f346bd1e3cb@arm.com> <20161014151827.GA10379@linaro.org> <2bb765e7-8a5f-c525-a6ae-fbec6fae6354@canonical.com> <20161017090903.GA11962@linaro.org> <4e15ad55-beeb-e860-0420-8f439d076758@arm.com> <20161017131952.GR3117@twins.programming.kicks-ass.net> Cc: Joseph Salisbury , Ingo Molnar , Linus Torvalds , Thomas Gleixner , LKML , Mike Galbraith , omer.akram@canonical.com From: Dietmar Eggemann Message-ID: <94cc6deb-f93e-60ec-5834-e84a8b98e73c@arm.com> Date: Mon, 17 Oct 2016 23:52:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2684 Lines: 56 On 10/17/2016 02:54 PM, Vincent Guittot wrote: > On 17 October 2016 at 15:19, Peter Zijlstra wrote: >> On Mon, Oct 17, 2016 at 12:49:55PM +0100, Dietmar Eggemann wrote: [...] >>> BTW, I guess we can reach .tg_load_avg up to ~300000-400000 on such a system >>> initially because systemd will create all ~100 services (and therefore the >>> corresponding 2. level tg's) at once. In my previous example, there was 500ms >>> between the creation of 2 tg's so there was a lot of decaying going on in between. >> >> Cute... on current kernels that translates to simply removing the call >> to update_tg_load_avg(), lets see if we can figure out what goes >> sideways first though, because it _should_ decay back out. And if that > > yes, Reaching ~300000-400000 is not an issue in itself, the problem is > that load_avg has decayed but it has not been reflected in > tg->load_avg in the buggy case > >> can fail here, I'm not seeing why that wouldn't fail elsewhere either. >> >> I'll see if I can reproduce this with a script creating heaps of cgroups >> in a hurry, I have a total lack of system-disease on all my machines. Something looks weird related to the use of for_each_possible_cpu(i) in online_fair_sched_group() on my i5-3320M CPU (4 logical cpus). In case I print out cpu id and the cpu masks inside the for_each_possible_cpu(i) I get: [ 5.462368] cpu=0 cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462370] cpu=1 cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462370] cpu=2 cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462371] cpu=3 cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462372] *cpu=4* cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462373] *cpu=5* cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462374] *cpu=6* cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 [ 5.462375] *cpu=7* cpu_possible_mask=0-7 cpu_online_mask=0-3 cpu_present_mask=0-3 cpu_active_mask=0-3 T430:/sys/fs/cgroup/cpu,cpuacct/system.slice# ls -l | grep '^d' | wc -l 80 /proc/sched_debug: cfs_rq[0]:/system.slice ... .tg_load_avg : 323584 ... 80 * 1024 * 4 (not existent cpu4-cpu7) = 327680 (with a little bit of decay, this could be this extra load on the systen.slice tg) Using for_each_online_cpu(i) instead of for_each_possible_cpu(i) in online_fair_sched_group() works on this machine, i.e. the .tg_load_avg of system.slice tg is 0 after startup.