From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757293AbcJMVf0 (ORCPT ); Thu, 13 Oct 2016 17:35:26 -0400 Received: from mail-lf0-f47.google.com ([209.85.215.47]:36476 "EHLO mail-lf0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751146AbcJMVfR (ORCPT ); Thu, 13 Oct 2016 17:35:17 -0400 MIME-Version: 1.0 In-Reply-To: <43c59cba-2044-1de2-0f78-8f346bd1e3cb@arm.com> References: <57F7F9AF.2010609@canonical.com> <20161008080019.GE3142@twins.programming.kicks-ass.net> <20161008083936.GA13658@gmail.com> <1475927349.5573.1.camel@gmx.de> <57FE6302.6060103@canonical.com> <57FFADC8.2020602@canonical.com> <43c59cba-2044-1de2-0f78-8f346bd1e3cb@arm.com> From: Vincent Guittot Date: Thu, 13 Oct 2016 23:34:55 +0200 Message-ID: Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes To: Dietmar Eggemann Cc: Joseph Salisbury , Ingo Molnar , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , LKML , Mike Galbraith Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13 October 2016 at 20:49, Dietmar Eggemann wrote: > On 13/10/16 17:48, Vincent Guittot wrote: >> On 13 October 2016 at 17:52, Joseph Salisbury >> wrote: >>> On 10/13/2016 06:58 AM, Vincent Guittot wrote: >>>> Hi, >>>> >>>> On 12 October 2016 at 18:21, Joseph Salisbury >>>> wrote: >>>>> On 10/12/2016 08:20 AM, Vincent Guittot wrote: >>>>>> On 8 October 2016 at 13:49, Mike Galbraith wrote: >>>>>>> On Sat, 2016-10-08 at 13:37 +0200, Vincent Guittot wrote: >>>>>>>> On 8 October 2016 at 10:39, Ingo Molnar wrote: >>>>>>>>> * Peter Zijlstra wrote: >>>>>>>>> >>>>>>>>>> On Fri, Oct 07, 2016 at 03:38:23PM -0400, Joseph Salisbury wrote: >>>>>>>>>>> Hello Peter, >>>>>>>>>>> >>>>>>>>>>> A kernel bug report was opened against Ubuntu [0]. After a >>>>>>>>>>> kernel >>>>>>>>>>> bisect, it was found that reverting the following commit >>>>>>>>>>> resolved this bug: >>>>>>>>>>> >>>>>>>>>>> commit 3d30544f02120b884bba2a9466c87dba980e3be5 >>>>>>>>>>> Author: Peter Zijlstra >>>>>>>>>>> Date: Tue Jun 21 14:27:50 2016 +0200 >>>>>>>>>>> >>>>>>>>>>> sched/fair: Apply more PELT fixes >>>>>>>> This patch only speeds up the update of task group load in order to >>>>>>>> reflect the new load balance but It should not change the final value >>>>>>>> and as a result the final behavior. I will try to reproduce it in my >>>>>>>> target later today >>>>>>> FWIW, I tried and failed w/wo autogroup on 4.8 and master. >>>>>> Me too >>>>>> >>>>>> Is it possible to get some dump of /proc/sched_debug while the problem occurs ? >>>>>> >>>>>> Vincent >>>>>> >>>>>>> -Mike >>>>> The output from /proc/shed_debug can be seen here: >>>>> http://paste.ubuntu.com/23312351/ >>>> I have looked at the dump and there is something very odd for >>>> system.slice task group where the display manager is running. >>>> system.slice->tg_load_avg is around 381697 but tg_load_avg is >>>> normally equal to Sum of system.slice[cpu]->tg_load_avg_contrib >>>> whereas Sum of system.slice[cpu]->tg_load_avg_contrib = 1013 in our >>>> case. We can have some differences because the dump of >>>> /proc/shed_debug is not atomic and some changes can happen but nothing >>>> like this difference. >>>> >>>> The main effect of this quite high value is that the weight/prio of >>>> the sched_entity that represents system.slice in root cfs_rq is very >>>> low (lower than task with the smallest nice prio) so the system.slice >>>> task group will not get the CPU quite often compared to the user.slice >>>> task group: less than 1% for the system.slice where lightDM and xorg >>>> are running compared 99% for the user.slice where the stress tasks are >>>> running. This is confirmed by the se->avg.util_avg value of the task >>>> groups which reflect how much time each task group is effectively >>>> running on a CPU: >>>> system.slice[CPU3].se->avg.util_avg = 8 whereas >>>> user.slice[CPU3].se->avg.util_avg = 991 >>>> >>>> This difference of weight/priority explains why the system becomes >>>> unresponsive. For now, I can't explain is why >>>> system.slice->tg_load_avg = 381697 whereas is should be around 1013 >>>> and how the patch can generate this situation. >>>> >>>> Is it possible to have a dump of /proc/sched_debug before starting >>>> stress command ? to check if the problem is there from the beginning >>>> but not seen because not overloaded. Or if it the problem comes when >>>> user starts to load the system >>> Here is the dump before stress is started: >>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1627108/+attachment/4760437/+files/dump_nonbuggy >> >> This one is ok. >> The dump indicates Sched Debug Version: v0.11, 4.8.0-11-generic >> #12~lp1627108Commit3d30544Reverted >> so this is without the culprit commit >> >>> >>> Here it is after: >>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1627108/+attachment/4760436/+files/dump_buggy >>> >> >> This one has the exact same odds values for system.slice->tg_load_avg >> than the 1st dump that you sent yesterday >> The dump indicates Sched Debug Version: v0.11, 4.8.0-22-generic #24-Ubuntu >> So this dump has been done with a different kernel than for the dump above. >> As I can't find any stress task in the dump, i tend to believe that >> the dump has been done before starting the stress tasks and not after >> starting them. Can you confirm ? >> >> If i'm right, it mean that the problem was already there before >> starting stress tasks. > > Could it be a problem I'm also seeing on my ARM64 Juno (6 logical cpus) w/o systemd > and w/o autogroup (tip/sched/core 447976ef4fd0): > > When I create a tg_root/tg_x/tg_y_1 and a tg_root/tg_x/tg_y_2 group, the tg_x->load_avg > becomes > 6*1024 before any tasks ran in it. This is normal as se->avg.load_avg is initialized to scale_load_down(se->load.weight) and this se->avg.load_avg will be added to tg_x[cpu]->cfs_rq->avg.load_avg when attached to the cfs_rq > > tg_x : 0xffff800975800d80 > tg_y_1 : 0xffff800975800c00 > tg_y_2 : 0xffff80097543d200 > > mkdir-2177 [002] 117.235241: bprint: sched_online_group: tg=0xffff800975800d80 tg->parent=0xffff000008fd0300 > mkdir-2177 [002] 117.235244: bprint: online_fair_sched_group: tg=0xffff800975800d80 cpu=0 > mkdir-2177 [002] 117.235247: bprint: online_fair_sched_group: tg=0xffff800975800d80 cpu=1 > mkdir-2177 [002] 117.235249: bprint: online_fair_sched_group: tg=0xffff800975800d80 cpu=2 > mkdir-2177 [002] 117.235251: bprint: online_fair_sched_group: tg=0xffff800975800d80 cpu=3 > mkdir-2177 [002] 117.235253: bprint: online_fair_sched_group: tg=0xffff800975800d80 cpu=4 > mkdir-2177 [002] 117.235255: bprint: online_fair_sched_group: tg=0xffff800975800d80 cpu=5 > > mkdir-2181 [002] 117.353155: bprint: sched_online_group: tg=0xffff800975800c00 tg->parent=0xffff800975800d80 > mkdir-2181 [002] 117.353158: bprint: online_fair_sched_group: tg=0xffff800975800c00 cpu=0 > mkdir-2181 [002] 117.353162: bprint: post_init_entity_util_avg: cpu=0 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=0 cfs_rq->avg.load_avg=1024 cfs_rq->tg_load_avg_contrib=0 delta=1024 > mkdir-2181 [002] 117.353164: bprint: online_fair_sched_group: tg=0xffff800975800c00 cpu=1 > mkdir-2181 [002] 117.353167: bprint: post_init_entity_util_avg: cpu=1 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=1024 cfs_rq->avg.load_avg=1024 cfs_rq->tg_load_avg_contrib=0 delta=1024 > mkdir-2181 [002] 117.353168: bprint: online_fair_sched_group: tg=0xffff800975800c00 cpu=2 > mkdir-2181 [002] 117.353171: bprint: post_init_entity_util_avg: cpu=2 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=2048 cfs_rq->avg.load_avg=1024 cfs_rq->tg_load_avg_contrib=0 delta=1024 > mkdir-2181 [002] 117.353173: bprint: online_fair_sched_group: tg=0xffff800975800c00 cpu=3 > mkdir-2181 [002] 117.353175: bprint: post_init_entity_util_avg: cpu=3 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=3072 cfs_rq->avg.load_avg=1024 cfs_rq->tg_load_avg_contrib=0 delta=1024 > mkdir-2181 [002] 117.353177: bprint: online_fair_sched_group: tg=0xffff800975800c00 cpu=4 > mkdir-2181 [002] 117.353179: bprint: post_init_entity_util_avg: cpu=4 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=4096 cfs_rq->avg.load_avg=1024 cfs_rq->tg_load_avg_contrib=0 delta=1024 > mkdir-2181 [002] 117.353180: bprint: online_fair_sched_group: tg=0xffff800975800c00 cpu=5 > mkdir-2181 [002] 117.353183: bprint: post_init_entity_util_avg: cpu=5 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=5120 cfs_rq->avg.load_avg=1024 cfs_rq->tg_load_avg_contrib=0 delta=1024 > This looks coherent as tg_x->load_avg = 5120 == sum of cfs_rq[cpu]->load_avg and cfs_rq->tg_load_avg_contrib will be set to cfs_rq[cpu]->load_avg at the end of the function call In the buggy case, tg->load_avg = 381697 but sum of cfs_rq[cpu]->tg_load_avg_contrib = 1013 = cfs_rq[cpu]->avg.load_avg so there is no way to remove the 381697 > mkdir-2185 [001] 117.502980: bprint: sched_online_group: tg=0xffff80097543d200 tg->parent=0xffff800975800d80 > mkdir-2185 [001] 117.502982: bprint: online_fair_sched_group: tg=0xffff80097543d200 cpu=0 > mkdir-2185 [001] 117.502987: bprint: post_init_entity_util_avg: cpu=0 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=6144 cfs_rq->avg.load_avg=1068 cfs_rq->tg_load_avg_contrib=1024 delta=44 > mkdir-2185 [001] 117.502988: bprint: online_fair_sched_group: tg=0xffff80097543d200 cpu=1 > mkdir-2185 [001] 117.502992: bprint: post_init_entity_util_avg: cpu=1 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=6188 cfs_rq->avg.load_avg=1058 cfs_rq->tg_load_avg_contrib=1024 delta=34 > mkdir-2185 [001] 117.502993: bprint: online_fair_sched_group: tg=0xffff80097543d200 cpu=2 > mkdir-2185 [001] 117.502996: bprint: post_init_entity_util_avg: cpu=2 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=6222 cfs_rq->avg.load_avg=1092 cfs_rq->tg_load_avg_contrib=1024 delta=68 > mkdir-2185 [001] 117.502998: bprint: online_fair_sched_group: tg=0xffff80097543d200 cpu=3 > mkdir-2185 [001] 117.503001: bprint: post_init_entity_util_avg: cpu=3 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=6290 cfs_rq->avg.load_avg=1069 cfs_rq->tg_load_avg_contrib=1024 delta=45 > mkdir-2185 [001] 117.503002: bprint: online_fair_sched_group: tg=0xffff80097543d200 cpu=4 > mkdir-2185 [001] 117.503005: bprint: post_init_entity_util_avg: cpu=4 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=6335 cfs_rq->avg.load_avg=1064 cfs_rq->tg_load_avg_contrib=1024 delta=40 > mkdir-2185 [001] 117.503006: bprint: online_fair_sched_group: tg=0xffff80097543d200 cpu=5 > mkdir-2185 [001] 117.503009: bprint: post_init_entity_util_avg: cpu=5 tg=0xffff800975800d80 tg_css_id=2 cfs_rq->tg->load_avg=*6375* cfs_rq->avg.load_avg=1061 cfs_rq->tg_load_avg_contrib=1024 delta=37 > > We add delta=1024 to tg_x->load_avg during tg_root/tg_x/tg_y_1 initialization but only > delta=~40 for tg_root/tg_x/tg_y_2. IMO, this comes from the decay of tg_y_2->se[cpu]->avg.load_avg before being attached to tg_x But I don't think that it's the same issue as the tg_x->load_avg is still coherent with the sum of cfs_rq->avg.load_avg and the sume of cfs_rq->tg_load_avg_contrib > > system.slice->tg_load_avg = 381697 is still pretty much higher and AFAICS, it's an > i5-5300U CPU so only 4 logical cpus. > > How many system.slice/foo's actually exists in this system? I only see user.slice There is several dozen of childs in system.slice but all > related cfs_rq[x]:/autogroups-xxx on my Ubuntu-16.04 Desktop system. > > [...]