netdev - Re: 10GBE performance drop with net.ipv4.tcp

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Date:	Wed, 20 Jun 2012 09:22:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>
Cc:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: 10GBE performance drop with net.ipv4.tcp_timestamps=0

On Wed, 2012-06-20 at 09:00 +0200, Stefan Priebe - Profihost AG wrote:
> Am 19.06.2012 23:31, schrieb Eric Dumazet:
> > On Tue, 2012-06-19 at 23:08 +0200, Stefan Priebe wrote:
> >> i'm testing 10GBE speed with tweo servers. One with 3.5-rc3 nd thoe
> >> other one whith RHEL 6 (2.6.32 kernel).
> >>
> >> I noticed that setting
> >> net.ipv4.tcp_timestamps=0
> >>
> >> descreased the performance from 9,7 Full Duplex to 3-4Gb/s.
> >>
> >> Is this bahviour fine? What should / could i tet?
> >>
> >
> > Really, you should provide more input than that, if you really want us
> > to help.
> 
> *arg* forgot to add the pastebin links. Sorry. Speed degraded in this 
> case from 9,88Gbit/s to 2,45Gbit/s. When i turn on timestamps it's 
> perfect again. Server A has 3.5.0-rc3 and server B has an RHEL6 2.6.32 
> kernel.
> 
> Before:
> http://pastebin.com/raw.php?i=1gVraWVc
> 
> After:
> http://pastebin.com/raw.php?i=NSh8Y29s

You have a lot of packet losses

add "tc -s -d qdisc" , "ifconfig -a " and "ethtool -S ethX" outputs for
both servers


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