linux-kernel - Re: utime accounting regression since 4.6 (was: Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps)

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Message-ID: <1475238950.19362.3.camel@redhat.com>
Date:   Fri, 30 Sep 2016 08:35:50 -0400
From:   Rik van Riel <riel@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Sonny Rao <sonnyrao@...omium.org>, Jann Horn <jann@...jh.net>,
        Robert Foss <robert.foss@...labora.com>, corbet@....net,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        John Stultz <john.stultz@...aro.org>,
        ross.zwisler@...ux.intel.com, jmarchan@...hat.com,
        Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Robin Humble <plaguedbypenguins@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        eric.engestrom@...tec.com, Janis Danisevskis <jdanis@...gle.com>,
        calvinowens@...com, Alexey Dobriyan <adobriyan@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        ldufour@...ux.vnet.ibm.com, linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ben Zhang <benzh@...omium.org>,
        Bryan Freed <bfreed@...omium.org>,
        Filipe Brandenburger <filbranden@...omium.org>,
        Mateusz Guzik <mguzik@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Mike Galbraith <mgalbraith@...e.com>
Subject: Re: utime accounting regression since 4.6 (was: Re: [PACTH v2 0/3]
 Implement /proc/<pid>/totmaps)

On Fri, 2016-09-30 at 11:49 +0200, Michal Hocko wrote:
> [CC Mike and Mel as they have seen some accounting oddities
>  when doing performance testing. They can share details but
>  essentially the system time just gets too high]
> 
> For your reference the email thread started
> http://lkml.kernel.org/r/20160823143330.GL23577@dhcp22.suse.cz
> 
> I suspect this is mainly for short lived processes - like kernel
> compile
> $ /usr/bin/time -v make mm/mmap.o
> [...]
>         User time (seconds): 0.45
>         System time (seconds): 0.82
>         Percent of CPU this job got: 111%
>         Elapsed (wall clock) time (h:mm:ss or m:ss): 0:01.14
> $ rm mm/mmap.o
> $ /usr/bin/time -v make mm/mmap.o
> [...]
>         User time (seconds): 0.47
>         System time (seconds): 1.55
>         Percent of CPU this job got: 107%
>         Elapsed (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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