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

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Message-ID: <4FE192A1.6000000@profihost.ag>
Date:	Wed, 20 Jun 2012 11:06:41 +0200
From:	Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: 10GBE performance drop with net.ipv4.tcp_timestamps=0

Am 20.06.2012 10:41, schrieb Eric Dumazet:
> On Wed, 2012-06-20 at 10:21 +0200, Stefan Priebe - Profihost AG wrote:
>> Am 20.06.2012 09:22, schrieb Eric Dumazet:
> Yes, you already told that in subject line.
>
> single tcp flow ?
I use iperf - i think it uses just a single tcp flow. But i'm not sure.

> You seem to have a switch or something that drops packets in this case.
> You could try to rate limit to 9Gb/s and see if it is better.
Sadly i can't rate limit to 9Gbit/s on the switch.

> Here, I roughly have same bandwidth with tcp_timestamps on or off, with
> ixgbe cards and net-next kernels.
Mhm strange. Do you have any vague idea what could cause this? Any wrong 
reordering of the packets without tcp_timestamps?

Stefan
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