netdev - Re: [PATCH 0/2] Get rid of ndo_xmit

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Message-ID: <20140827155651.04fe49d0@redhat.com>
Date:	Wed, 27 Aug 2014 15:56:51 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	therbert@...gle.com, jhs@...atatu.com, edumazet@...gle.com,
	jeffrey.t.kirsher@...el.com, rusty@...tcorp.com.au,
	dborkman@...hat.com, brouer@...hat.com
Subject: Re: [PATCH 0/2] Get rid of ndo_xmit_flush

On Wed, 27 Aug 2014 06:23:58 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> I am afraid Jesper tests are not complete to truly have a picture of the
> extra costs, because he made sure no false sharing was possible (A
> single cpu does everything and keeps skb in its cache)

I fully agree. My tests a very artificial benchmarks only for the
optimal case.

I do worry a bit, if writing skb->xmit_more in a more cache cold
scenarios could hurt us (as that cacheline seems to be read mostly),
but this is not a problem right now because it will always be cache
hot, as we always clear the entire SKB in alloc.

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