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

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Message-ID: <20170512161915.GA4185@amt.cnet>
Date:   Fri, 12 May 2017 13:19:16 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Christoph Lameter <cl@...ux.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, May 12, 2017 at 11:07:48AM -0500, Christoph Lameter wrote:
> 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 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.

> 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?