Re: [RFC PATCH v3] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too

[Aaron Tomlin]

On Mon 2022-04-25 16:21 -0300, Marcelo Tosatti wrote:
> > Hi Peter, Christoph,
> > 
> > Indeed. Which was why I decided, initially, against the general-purpose
> > case/or approach. Personally, I would prefer to keep this somewhat
> > restrictive to nohz.
> 
> Is there anything that prevents a nohz full CPU from running an
> application with short and frequent idling?

Hi Marcelo,

I'm not sure I understand the question; albeit, if I understand correctly,
yes: the scheduling-clock tick, if it was stopped.
Yet I believe this behaviour is correct. Consider the following example:

  When a CFS task is moved/or migrated to a nohz_full CPU that was
  previously idle and had its tick stopped, if its the only task on the
  run-queue then it is possible that the idle task may not restart the
  tick (see __tick_nohz_full_update_tick()).  Thus once the CFS task exits
  manual intervention i.e. a reschedule IPI to wake the idle task, would be
  required to run again, on the same CPU.



Kind regards,

-- 
Aaron Tomlin