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From: Jesse Brandeburg <jesse.brandeburg@intel.com>
Subject: Re: [RFC PATCH 00/12] Implement XDP bpf_redirect vairants
Date: Mon, 17 Jul 2017 10:04:44 -0700
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Cc: John Fastabend <john.fastabend@gmail.com>,
        David Miller <davem@davemloft.net>, <netdev@vger.kernel.org>,
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To: Jesper Dangaard Brouer <brouer@redhat.com>
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On Sun, 16 Jul 2017 10:23:08 +0200
Jesper Dangaard Brouer <brouer@redhat.com> wrote:

> On Tue, 11 Jul 2017 12:37:10 -0700 John Fastabend <john.fastabend@gmail.com> wrote:
> 
>  [...]  
> > 
> > hmm maybe Jesse or Alex have some clues. Adding them to the CC list.  
> 
> This seems related to Hyper-Threading.  I tried to disable
> hyperthreading in the BIOS, and the problem goes away.  That is, the
> benchmarks are no-longer affected by the CPU tuned-adm profile.

Wow, nice job figuring that out.  I went and took a look at tuned-adm
documentation but didn't see anything that stood out that would cause
the behavior you were seeing.

I suspect your toplev results showing this is a frontend problem mesh
nicely with the hyper-threading configuration inducing the bad behavior,
since there is still only one execution unit, and the fetchers would
have to stall.  I think you've rediscovered why the forwarding /
routing crowd generally turns off hyperthreading.