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-XoJtRXgx1JtgGdypvdXH1w@public.gmane.org/

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