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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <48A41139.9080509@trash.net>
Date:	Thu, 14 Aug 2008 13:04:25 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	David Miller <davem@...emloft.net>
CC:	alex.williamson@...com, akpm@...ux-foundation.org,
	buytenh@...vell.com, netdev@...r.kernel.org,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bugme-new] [Bug 11316] New: severe performance regression for
 iptables nat routing

David Miller wrote:
> 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.

I don't think so, its using skb_make_writable everywhere, which checks
for skb_clone_writable, which should usually avoid COWing local TCP
packets. It would also be unlikely to have that much of a performance
impact (1MB/s -> 34kb/s).

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

Alex, could you post a tcpdump from both loopback and the outgoing
device from the machine you're doing NAT on?
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html