netdev - Re: REDIRECT in nat OUTPUT

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Date:	Sun, 13 Jul 2008 16:59:27 +0200 (CEST)
From:	Krzysztof Oledzki <olel@....pl>
To:	Denys Fedoryshchenko <denys@...p.net.lb>
cc:	Evgeniy Polyakov <johnpol@....mipt.ru>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: REDIRECT in nat OUTPUT



On Sun, 13 Jul 2008, Denys Fedoryshchenko wrote:

> On Sunday 13 July 2008, Evgeniy Polyakov wrote:
>> On Sat, Jul 12, 2008 at 05:40:25PM +0300, Denys Fedoryshchenko (denys@...p.net.lb) wrote:
>>> Seems i found something. After issuing ethtool -K lo tso on i got significant performance improvement.
>>> Why it is not on by default?
>>> Without it performance is VERY poor.
>>
>> TSO over loopback turns to be GSO, which allows to aggregate multiple
>> packets into single frame. If system is not CPU bound, then it is likely
>> REDIRECT problem. If I understood you corerctly, loopback performance is
>> always good without REDIRECT, but fails to miserable level when
>> apprpriate rule is used?
>>
> No, seems it has performance issues without redirect(and conntrack unloaded too) even, iperf results on loopback is very unstable.
>
> Actually i dont understand, how on idle machine with Xeon processor iperf over loopback (tcp) can be ~100Mbps?
> I think it is a bug.

Something is wrong here as:

root@...-t:~# iperf -c 127.1
------------------------------------------------------------
Client connecting to 127.1, TCP port 5001
TCP window size: 49.2 KByte (default)
------------------------------------------------------------
[  3] local 127.0.0.1 port 36419 connected with 127.0.0.1 port 5001
[  3]  0.0-10.0 sec  7.10 GBytes  6.10 Gbits/sec

# uname -r
2.6.24.7-o4

# grep "model name" /proc/cpuinfo|uniq
model name      : Intel(R) Xeon(R) CPU           X5460  @ 3.16GHz

Best regards,

 			Krzysztof Olędzki