linux-kernel - Re: iptables very slow after commit 784544739a25c30637397ace5489eeb6e15d7d49

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Date:	Sun, 12 Apr 2009 00:05:34 +0800
From:	Jeff Chua <jeff.chua.linux@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Jan Engelhardt <jengelh@...ozas.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>, dada1@...mosbay.com,
	kaber@...sh.net, r000n@...0n.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: iptables very slow after commit 784544739a25c30637397ace5489eeb6e15d7d49

On Sat, Apr 11, 2009 at 11:07 PM, Stephen Hemminger
<shemminger@...tta.com> wrote:
>> iptables works in whole tables. Userspace submits a table, checkentry is
>> called for all rules in the new table, things are swapped, then destroy
>> is called for all rules in the old table. By that logic (which existed
>> since dawn I think), only the swap operation needs to be locked.
> Part of the overhead is the API choice to take counter values from user
> space during the replace.  If the rule replacement just always started with
> zero counters it could be done with less overhead.

It's always good practice to start from zero with these ...

# iptables -F
# iptables -t nat -F
# iptables -X

And most of the time, rules should be put into a file so that it can
rerun easily after reboot. So if it can be speed up for just this
case, it'll help many out there.

Thanks,
Jeff.
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