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Date:	Sun, 13 Jul 2008 17:19:50 +0300
From:	Denys Fedoryshchenko <>
To:	Evgeniy Polyakov <>
	David Miller <>,
	Eric Dumazet <>
Subject: Re: REDIRECT in nat OUTPUT

On Sunday 13 July 2008, Evgeniy Polyakov wrote:
> On Sat, Jul 12, 2008 at 05:40:25PM +0300, Denys Fedoryshchenko ( 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.

Technical Manager
Virtual ISP S.A.L.
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