From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: Joseph Salisbury <joseph.salisbury@canonical.com>,
Ingo Molnar <mingo@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Mike Galbraith <efault@gmx.de>,
omer.akram@canonical.com
Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes
Date: Mon, 17 Oct 2016 23:52:39 +0100 [thread overview]
Message-ID: <94cc6deb-f93e-60ec-5834-e84a8b98e73c@arm.com> (raw)
In-Reply-To: <CAKfTPtAxw1b-vy285HKtPUBFYuJdv2CFZH_gP3CMtZHs1wLPXg@mail.gmail.com>
On 10/17/2016 02:54 PM, Vincent Guittot wrote:
> On 17 October 2016 at 15:19, Peter Zijlstra <peterz@infradead.org> 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.
next prev parent reply other threads:[~2016-10-17 22:52 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-07 19:38 [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes Joseph Salisbury
2016-10-07 19:57 ` Linus Torvalds
2016-10-07 20:22 ` Joseph Salisbury
2016-10-07 20:37 ` Linus Torvalds
2016-10-08 8:00 ` Peter Zijlstra
2016-10-08 8:39 ` Ingo Molnar
2016-10-08 11:37 ` Vincent Guittot
2016-10-08 11:49 ` Mike Galbraith
2016-10-12 12:20 ` Vincent Guittot
2016-10-12 15:35 ` Joseph Salisbury
2016-10-12 16:21 ` Joseph Salisbury
2016-10-13 10:58 ` Vincent Guittot
2016-10-13 15:52 ` Joseph Salisbury
2016-10-13 16:48 ` Vincent Guittot
2016-10-13 18:49 ` Dietmar Eggemann
2016-10-13 21:34 ` Vincent Guittot
2016-10-14 8:24 ` Vincent Guittot
2016-10-14 13:10 ` Dietmar Eggemann
2016-10-14 15:18 ` Vincent Guittot
2016-10-14 16:04 ` Joseph Salisbury
2016-10-17 9:09 ` Vincent Guittot
2016-10-17 11:49 ` Dietmar Eggemann
2016-10-17 13:19 ` Peter Zijlstra
2016-10-17 13:54 ` Vincent Guittot
2016-10-17 22:52 ` Dietmar Eggemann [this message]
2016-10-18 8:43 ` Vincent Guittot
2016-10-18 9:07 ` Peter Zijlstra
2016-10-18 9:45 ` Vincent Guittot
2016-10-18 10:34 ` Peter Zijlstra
2016-10-18 11:56 ` Vincent Guittot
2016-10-18 21:58 ` Joonwoo Park
2016-10-19 6:42 ` Vincent Guittot
2016-10-19 9:46 ` Dietmar Eggemann
2016-10-19 11:25 ` Vincent Guittot
2016-10-19 15:33 ` Dietmar Eggemann
2016-10-19 17:33 ` Joonwoo Park
2016-10-19 17:50 ` Vincent Guittot
2016-10-19 11:33 ` Peter Zijlstra
2016-10-19 11:50 ` Vincent Guittot
2016-10-19 13:30 ` Morten Rasmussen
2016-10-19 17:41 ` Vincent Guittot
2016-10-20 7:56 ` Morten Rasmussen
2016-10-19 14:49 ` Joseph Salisbury
2016-10-19 14:53 ` Vincent Guittot
2016-10-18 11:15 ` Dietmar Eggemann
2016-10-18 12:07 ` Peter Zijlstra
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