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 - 10:17:29 EST

On Mon 2022-04-25 15:27 +0200, Peter Zijlstra wrote:
> On Mon, Apr 25, 2022 at 02:09:06PM +0200, Christoph Lameter wrote:
> > On Mon, 25 Apr 2022, Aaron Tomlin wrote:
> >
> > > Yes, in the context of nohz, this patch should ensure it, if required, when
> > > the idle tick is to be stopped.
> >
> > What I said was that it is generally useful. Even in the non NOHZ case.
> >
> > Folding the vmstat diffs *always* when entering idle prevents unnecessary
> > wakeups and processing in the future and also provides more accurate
> > counters for the VM allowing better decision to be made on reclaim.
> I'm thinking you're going to find a ton of regressions if you try it
> though; some workloads go idle *very* shortly, doing all this accounting
> is going to be counter-productive.

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.

Kind regards,

Aaron Tomlin