linux-kernel - Re: [patch 2/2] MM: allow per-cpu vmstat_threshold and vmstat

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Message-ID: <alpine.DEB.2.20.1705121154240.23503@east.gentwo.org>
Date:   Fri, 12 May 2017 11:57:15 -0500 (CDT)
From:   Christoph Lameter <cl@...ux.com>
To:     Marcelo Tosatti <mtosatti@...hat.com>
cc:     Luiz Capitulino <lcapitulino@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Rik van Riel <riel@...hat.com>,
        Linux RT Users <linux-rt-users@...r.kernel.org>,
        cmetcalf@...lanox.com
Subject: Re: [patch 2/2] MM: allow per-cpu vmstat_threshold and vmstat_worker
 configuration

On Fri, 12 May 2017, Marcelo Tosatti wrote:

> > What exactly is the issue you are seeing and want to address? I think we
> > have similar aims and as far as I know the current situation is already
> > good enough for what you may need. You may just not be aware of how to
> > configure this.
>
> I want to disable vmstat worker thread completly from an isolated CPU.
> Because it adds overhead to a latency target, target which
> the lower the better.

NOHZ already does that. I wanted to know what your problem is that you
see. The latency issue has already been solved as far as I can tell .
Please tell me why the existing solutions are not sufficient for you.

> > I doubt that doing inline updates will do much good compared to what we
> > already have and what the dataplan mode can do.
>
> Can the dataplan mode disable vmstat worker thread completly on a given
> CPU?

That already occurs when you call quiet_vmstat() and is used by the NOHZ
logic. Configure that correctly and you should be fine.