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

From: Aaron Tomlin
Date: Mon Apr 25 2022 - 07:39:23 EST

On Mon 2022-04-25 09:23 +0200, Christoph Lameter wrote:
> On Fri, 22 Apr 2022, Aaron Tomlin wrote:
> > A customer provided some evidence which indicates that the idle tick was
> > stopped; albeit, CPU-specific vmstat counters still remained populated.
> > Thus one can only assume quiet_vmstat() was not invoked on return to the
> > idle loop.
> Could we *always* fold the vmstat counters when entering idle mode? That
> would make the logic less complicated. There is nothing else to do since
> we are entering an idle state and if there are any counter deltas then we
> have the time to process them. This may also decrease the time that
> deltas exist significantly and an idle system will have accurate vmstat
> counters.

Hi Christoph,

Thank you for your feedback.

Yes, in the context of nohz, this patch should ensure it, if required, when
the idle tick is to be stopped.

Kind regards,

Aaron Tomlin