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

[Rik van Riel <riel@redhat.com>]

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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
>  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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