linux-kernel - Re: [PATCH v2 4/5] sched/cpuacct: fix user/system in shown cpuacct.usage*

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Date:   Fri, 10 Sep 2021 15:03:26 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Andrey Ryabinin <arbn@...dex-team.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        bharata@...ux.vnet.ibm.com, boris@....io, stable@...r.kernel.org
Subject: Re: [PATCH v2 4/5] sched/cpuacct: fix user/system in shown
 cpuacct.usage*

On Fri, Aug 20, 2021 at 12:40:04PM +0300, Andrey Ryabinin wrote:
> cpuacct has 2 different ways of accounting and showing user
> and system times.
> 
> The first one uses cpuacct_account_field() to account times
> and cpuacct.stat file to expose them. And this one seems to work ok.
> 
> The second one is uses cpuacct_charge() function for accounting and
> set of cpuacct.usage* files to show times. Despite some attempts to
> fix it in the past it still doesn't work. Sometimes while running KVM
> guest the cpuacct_charge() accounts most of the guest time as
> system time. This doesn't match with user&system times shown in
> cpuacct.stat or proc/<pid>/stat.
> 
> Demonstration:
>  # git clone https://github.com/aryabinin/kvmsample
>  # make
>  # mkdir /sys/fs/cgroup/cpuacct/test
>  # echo $$ > /sys/fs/cgroup/cpuacct/test/tasks
>  # ./kvmsample &
>  # for i in {1..5}; do cat /sys/fs/cgroup/cpuacct/test/cpuacct.usage_sys; sleep 1; done
>  1976535645
>  2979839428
>  3979832704
>  4983603153
>  5983604157

Thanks for expanding on this, and fixing broken cpuacct_charge.

For the series,
Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>