linux-kernel - Re: group scheduler regression since 4.3 (bisect 9d89c257d sched/fair: Rewrite runnable load and utilization average tracking)

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Message-Id: <b232f112-b766-8d92-142c-27cb09ec73e3@de.ibm.com>
Date:   Mon, 26 Sep 2016 14:49:53 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Yuyang Du <yuyang.du@...el.com>, Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        vincent.guittot@...aro.org, Morten.Rasmussen@....com,
        dietmar.eggemann@....com, pjt@...gle.com, bsegall@...gle.com
Subject: Re: group scheduler regression since 4.3 (bisect 9d89c257d
 sched/fair: Rewrite runnable load and utilization average tracking)

On 09/26/2016 02:10 PM, Peter Zijlstra wrote:
> On Mon, Sep 26, 2016 at 02:01:43PM +0200, Christian Borntraeger wrote:
>> They applied ok on next from 9/13. Things go even worse.
>> With this host configuration:
>>
>> CPU NODE BOOK SOCKET CORE L1d:L1i:L2d:L2i ONLINE CONFIGURED ADDRESS
>> 0   0    0    0      0    0:0:0:0         yes    yes        0
>> 1   0    0    0      0    1:1:1:1         yes    yes        1
>> 2   0    0    0      1    2:2:2:2         yes    yes        2
>> 3   0    0    0      1    3:3:3:3         yes    yes        3
>> 4   0    0    1      2    4:4:4:4         yes    yes        4
>> 5   0    0    1      2    5:5:5:5         yes    yes        5
>> 6   0    0    1      3    6:6:6:6         yes    yes        6
>> 7   0    0    1      3    7:7:7:7         yes    yes        7
>> 8   0    0    1      4    8:8:8:8         yes    yes        8
>> 9   0    0    1      4    9:9:9:9         yes    yes        9
>> 10  0    0    1      5    10:10:10:10     yes    yes        10
>> 11  0    0    1      5    11:11:11:11     yes    yes        11
>> 12  0    0    1      6    12:12:12:12     yes    yes        12
>> 13  0    0    1      6    13:13:13:13     yes    yes        13
>> 14  0    0    1      7    14:14:14:14     yes    yes        14
>> 15  0    0    1      7    15:15:15:15     yes    yes        15
>>
>> the guest was running either on 0-3 or on 4-15, but never
>> used the full system. With group scheduling disabled everything was good
>> again. So looks like that this bug has also some dependency on on the
>> host topology.
> 
> OK, so CPU affinities that unevenly straddle topology boundaries like
> that are hard (and is generally not recommended), but its not
> immediately obvious why it would be so much worse with cgroups enabled.

Well thats what I get from LPAR...
With CPUs 0-3 disabled things are better, but there is still 10%
difference between group/nogroup.
Will test Vincents v4 soon.

In any case, would a 5 second sequence of /proc/sched_debug for the
good/bad case with all 16 host CPUs  (or the reduced 12 cpu set) be useful?

Christian