From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 4 Sep 2002 08:27:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 4 Sep 2002 08:27:48 -0400 Received: from nixpbe.pdb.siemens.de ([192.109.2.33]:55737 "EHLO nixpbe.pdb.sbs.de") by vger.kernel.org with ESMTP id ; Wed, 4 Sep 2002 08:27:45 -0400 Subject: ip_conntrack_hash() problem From: Martin Wilck To: Netfilter Mailing List Cc: Linux Kernel mailing list , Rusty Russell , Patrick Schaaf , Harald Welte , Andreas Kleen Content-Type: text/plain Content-Transfer-Encoding: 7bit X-Mailer: Ximian Evolution 1.0.3 (1.0.3-6) Date: 04 Sep 2002 14:33:41 +0200 Message-Id: <1031142822.3314.116.camel@biker.pdb.fsc.net> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, I posted a patch to netfilter-devel a week ago that fixes a severe performance problem with ip_conntrack_hash() (see below). Harald rejected it (sort of), telling me I should have read past threads about the hash function first. http://marc.theaimsgroup.com/?l=netfilter-devel&m=103054090215896&w=2 I think I have to insist on this, though. Although it certainly isn't the "optimal" hash function for ip_conntrack, it fixes a problem that leads to extremely unbalanced hashing in some situations, in particular in a simple client<->router<->webserver scenario. In that case, all connection tuples from server to client, i.e. 50% of all tuples, end up in the same bucket(!), as I showed in my posting to netfilter-devel. This happens if the hash size is a power of 2, which is the default on most newer machines. The fix is rather trivial (mainly the port numbers are accounted for outside the ntohl() function), and therefore I'd like to ask again that it be applied. Unless I am mistaken, the past discussions were mainly concerned with fine-tuning of the hash function, which is a topic my patch doesn't address, and can easily be done on top of it. Regards, Martin -- Martin Wilck Phone: +49 5251 8 15113 Fujitsu Siemens Computers Fax: +49 5251 8 20409 Heinz-Nixdorf-Ring 1 mailto:Martin.Wilck@Fujitsu-Siemens.com D-33106 Paderborn http://www.fujitsu-siemens.com/primergy