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Subject: Re: utime accounting regression since 4.6 (was: Re: [PACTH v2 0/3]
 Implement /proc/<pid>/totmaps)
From: Rik van Riel <riel@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>, Sonny Rao <sonnyrao@chromium.org>,
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        Mateusz Guzik <mguzik@redhat.com>, Mel Gorman <mgorman@suse.de>,
        Mike Galbraith <mgalbraith@suse.com>
Date: Fri, 30 Sep 2016 08:35:50 -0400
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On Fri, 2016-09-30 at 11:49 +0200, Michal Hocko wrote:
> [CC Mike and Mel as they have seen some accounting oddities
> =C2=A0when doing performance testing. They can share details but
> =C2=A0essentially the system time just gets too high]
>=20
> For your reference the email thread started
> http://lkml.kernel.org/r/20160823143330.GL23577@dhcp22.suse.cz
>=20
> I suspect this is mainly for short lived processes - like kernel
> compile
> $ /usr/bin/time -v make mm/mmap.o
> [...]
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0User time (seconds): 0.45
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0System time (seconds): 0.=
82
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Percent of CPU this job g=
ot: 111%
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Elapsed (wall clock) time=
 (h:mm:ss or m:ss): 0:01.14
> $ rm mm/mmap.o
> $ /usr/bin/time -v make mm/mmap.o
> [...]
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0User time (seconds): 0.47
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0System time (seconds): 1.=
55
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Percent of CPU this job g=
ot: 107%
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Elapsed (wall clock) time=
 (h:mm:ss or m:ss): 0:01.88

I was not able to get the "expected" results from
your last reproducer, but this one does happen on
my system, too.

The bad news is, I still have no clue what is causing
it...

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