netdev - Re: Poor TCP bandwidth between network namespaces

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Message-ID: <1360373618.6696.2.camel@edumazet-glaptop>
Date:	Fri, 08 Feb 2013 17:33:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Emmanuel Jeanvoine <emmanuel.jeanvoine@...ia.fr>,
	netdev@...r.kernel.org
Subject: Re: Poor TCP bandwidth between network namespaces

On Mon, 2013-02-04 at 23:52 +0100, Hannes Frederic Sowa wrote:
> On Mon, Feb 04, 2013 at 03:43:20PM +0100, Emmanuel Jeanvoine wrote:
> > I'm wondering why the overhead is so high when performing TCP 
> > transfers between two network namespaces. Do you have any idea about 
> > this issue? And possibly, how to increase the bandwidth (without 
> > modifying the MTU on the veths) between network namespaces?
> 
> You could try Eric's patch (already in net-next) and have a look at the rest
> of the discussion:
> 
> http://article.gmane.org/gmane.linux.network/253589

Another thing to consider is the default MTU value :

65536 for lo, and 1500 for veth

It easily explains half performance for veth

One another thing is the tx-nocache-copy setting, this can explain some
extra percents.



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