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: <alpine.DEB.2.22.394.2204250919400.2367@gentwo.de>
Date:   Mon, 25 Apr 2022 09:23:01 +0200 (CEST)
From:   Christoph Lameter <cl@...two.de>
To:     Aaron Tomlin <atomlin@...hat.com>
cc:     frederic@...nel.org, mtosatti@...hat.com, tglx@...utronix.de,
        mingo@...nel.org, peterz@...radead.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 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.