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: <20220425113909.u3smtztp66svlw4o@ava.usersys.com>
Date:   Mon, 25 Apr 2022 12:39:09 +0100
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Christoph Lameter <cl@...two.de>
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 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