netdev - Re: [Bugme-new] [Bug 11316] New: severe performance regression for iptables nat routing

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Message-Id: <20080813.192101.221940876.davem@davemloft.net>
Date:	Wed, 13 Aug 2008 19:21:01 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	alex.williamson@...com
Cc:	akpm@...ux-foundation.org, buytenh@...vell.com,
	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org,
	kaber@...sh.net
Subject: Re: [Bugme-new] [Bug 11316] New: severe performance regression for
 iptables nat routing

From: Alex Williamson <alex.williamson@...com>
Date: Wed, 13 Aug 2008 20:08:20 -0600

> git bisect traced the problem back to this changeset:
> 
>         commit e5a4a72d4f88f4389e9340d383ca67031d1b8536
>         Author: Lennert Buytenhek <buytenh@...vell.com>
>         Date:   Sun Aug 3 01:23:10 2008 -0700
>         
>             net: use software GSO for SG+CSUM capable netdevices
> 
> I've verified that I can toggle the slowness by reverting this patch on
> top of 8d0968ab (current head).  The problem is readily reproducible
> using Ubuntu Hardy in a KVM VM with upstream, defconfig kernel.

Patrick I wonder if there a case where iptables NAT will COW the packet
when it really doesn't need to.

It seems, if anything, using GSO should make things go a little bit
faster not slower... Hmmm...

Anyways, if we can't figure this one out soon we can easily revert.
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