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

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Message-ID: <alpine.DEB.2.20.1705121103120.22831@east.gentwo.org>
Date:   Fri, 12 May 2017 11:07:48 -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:

> In our case, vmstat updates are very rare (CPU is dominated by DPDK).

What is the OS doing on the cores that DPDK runs on? I mean we here can
clean a processor of all activities and are able to run for a long time
without any interruptions.

Why would you still let the OS do things on that processor? If activities
by the OS are required then the existing NOHZ setup already minimizes
latency to a short burst (and Chris Metcalf's work improves on that).

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 doubt that doing inline updates will do much good compared to what we
already have and what the dataplan mode can do.