netdev - Re: [PATCH] softirq: let ksoftirqd do its job

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Date:   Fri, 2 Sep 2016 10:35:34 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        Rik van Riel <riel@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>, brouer@...hat.com
Subject: Re: [PATCH] softirq: let ksoftirqd do its job

On Thu, 1 Sep 2016 17:28:02 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Sep 01, 2016 at 03:30:42PM +0200, Jesper Dangaard Brouer wrote:
> > Still... enabled!
> > Hmmm.. more idea how to disable this???  
> 
> I think you ought to be able to assign yourself to the root cgroup,
> something like:
> 
>   echo $$ > /cgroup/tasks
> 
> or wheverever the cpu-cgroup controller is mounted at.
> 
> But its been a fair while since I touched any of that, its not a CONFIG
> I have enabled much.

I could not figure out how to disable autogroups, so I ended up
compiling the kernel without CONFIG_SCHED_AUTOGROUP.

  PID   PR   S  %CPU     TIME+ 	COMMAND
    3   20   R  20.7   0:53.05 	ksoftirqd/0
 9299   20   R  16.3   0:03.62 	udp_sink
 9296   20   S  16.0   0:03.59 	udp_sink
 9297   20   R  16.0   0:03.58 	udp_sink
 9298   20   R  16.0   0:03.57 	udp_sink
 9295   20   R  15.3   0:03.43 	udp_sink

Top new shows the CPU distribution is more correct, thus we can
concluded the artifact I saw was indeed caused by autogroup.

I can also confirm that my netperf UDP_STREAM tests now work again,
but I need around 32 parallel netperf to counter the effectiveness of
the ksoftirqd process.  While I only need 5 udp_sink programs.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer