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

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Date:   Mon, 25 Apr 2022 15:17:17 +0100
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Christoph Lameter <cl@...two.de>, frederic@...nel.org,
        mtosatti@...hat.com, tglx@...utronix.de, mingo@...nel.org,
        pauld@...hat.com, neelx@...hat.com, oleksandr@...alenko.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v3] tick/sched: Ensure quiet_vmstat() is called when
 the idle tick was stopped too

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