linux-kernel - Re: [PATCH] cgroup: Fix rootcg cpu.stat guest double counting

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Message-ID: <20211029172129.smeyk5adocjrwtlb@oracle.com>
Date:   Fri, 29 Oct 2021 13:21:29 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Dan Schatzberg <schatzberg.dan@...il.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Boris Burkov <boris@....io>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrey Ryabinin <arbn@...dex-team.com>
Subject: Re: [PATCH] cgroup: Fix rootcg cpu.stat guest double counting

On Thu, Oct 28, 2021 at 03:15:27PM -0700, Dan Schatzberg wrote:
> In account_guest_time in kernel/sched/cputime.c guest time is
> attributed to both CPUTIME_NICE and CPUTIME_USER in addition to
> CPUTIME_GUEST_NICE and CPUTIME_GUEST respectively. Therefore, adding
> both to calculate usage results in double counting any guest time at
> the rootcg.

Yes, definitely a bug.  The same fix was posted a couple months ago as
part of a series but never picked up:

  https://x-lore.kernel.org/all/20210820094005.20596-3-arbn@yandex-team.com/

The series also touched cputime, so we might be waiting for scheduler
folks?   +Ingo +Peter +Andrey