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

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