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

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Message-ID: <20220425132700.GK2731@worktop.programming.kicks-ass.net>
Date:   Mon, 25 Apr 2022 15:27:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Lameter <cl@...two.de>
Cc:     Aaron Tomlin <atomlin@...hat.com>, 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, 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.