linux-kernel - Re: [BUG nohz]: wrong user and system time accounting

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Message-ID: <20170329092357.2ca784c2@redhat.com>
Date:   Wed, 29 Mar 2017 09:23:57 -0400
From:   Luiz Capitulino <lcapitulino@...hat.com>
To:     Rik van Riel <riel@...hat.com>
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        Wanpeng Li <kernellwp@...il.com>
Subject: Re: [BUG nohz]: wrong user and system time accounting

On Wed, 29 Mar 2017 09:14:32 -0400
Rik van Riel <riel@...hat.com> wrote:

> > I failed to reproduce with your config. I'm still getting 99%
> > userspace
> > cputime. So I'm wondering if the hogging style plays a role.
> > 
> > I run pure user loops:
> > 
> >     int main(int argc, char **argv)
> >     {
> >         for (;;);
> >         return 0
> >     }
> > 
> > Does your user program perform syscalls or IOs of some sort?  
> 
> Luiz's program makes a syscall every millisecond,
> if started with the arguments he gave as his
> reproducer.

There are various reproducers actually. I started off with the simple
loop above, then wrote the attach program and then wrote the one
you're mentioning:

 http://people.redhat.com/~lcapitul/real-time/acct-bug.c

All of them reproduce the issue 100% of the time for me.

View attachment "hog.c" of type "text/x-c++src" (999 bytes)