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Date:	Mon, 18 Jun 2012 11:45:06 +0200
From:	Eric Dumazet <>
To:	Stefan Priebe - Profihost AG <>
Cc:	Linux Netdev List <>
Subject: Re: unstable 10GBE performance with recent kernels (> 3.0.X)

On Mon, 2012-06-18 at 11:22 +0200, Stefan Priebe - Profihost AG wrote:
> Hello list,
> i've discovered very unstable 10GBE performance using recent kernels. 
> I'm using some optimized settings mentioned by intel here 
> (part:Improving Performance): 

like what settings ?

> I'm using Intel X520 cards (ixgbe driver version: 3.9.17-NAPI in all 
> tests).
> I'm measuring the performance with iperf.
> With 3.0.32 i get constant 9,90 Gbit/s in both directions simultaneously.
> With 3.4.2 or 3.5.0-rc2 it get sometimes 9,9gbit/s - sometimes 3gbit/s 
> or even sometimes only 1gbit/s throughput.
> I also tried to change the tcp_congestion_control from cubic to reno, 
> bic and highspeed but no change.
> I also tried to bisect the issue but there are so many changes in the 
> net kernel part that i'm unable to identify the problem as with some 
> commits i only get 0-300kb/s performance.
> Any ideas?

ethtool -S eth0
ethtool -k eth0
netstat -s   (on sender, on receiver)

single flow , multiple flows ?

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