From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx2-b.sourceforge.net ([10.3.1.12] helo=sc8-sf-mx2.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1CFIYj-0005IO-If for user-mode-linux-devel@lists.sourceforge.net; Wed, 06 Oct 2004 13:38:49 -0700 Received: from cantor.suse.de ([195.135.220.2]) by sc8-sf-mx2.sourceforge.net with esmtp (TLSv1:DES-CBC3-SHA:168) (Exim 4.41) id 1CFIYi-0005bh-Ik for user-mode-linux-devel@lists.sourceforge.net; Wed, 06 Oct 2004 13:38:49 -0700 From: Andi Kleen Subject: Re: [uml-devel] uml "ip header error" for large (fragmented) udp packets Message-ID: <20041006203539.GC22794@wotan.suse.de> References: <200410061938.06648.blaisorblade_spam@yahoo.it> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: The user-mode Linux development list List-Post: List-Help: List-Subscribe: , List-Archive: Date: Wed, 6 Oct 2004 22:35:39 +0200 To: Lars Ellenberg , user-mode-linux-devel@lists.sourceforge.net, lmb@suse.de, ak@suse.de On Wed, Oct 06, 2004 at 08:48:23PM +0200, Lars Ellenberg wrote: > > So this could help you for now, while we try to find a clue about this. Quite > > frankly, I must say that I'm not seeing any network kernel hacker here > > (correct me if I'm wrong), so it will take some time to debug it. Maybe Gerd > > Knorr is an exception, actually. > > Well, then I take Andi Kleen and Lars Marowsky-Br?e into CC for now. > Lars, because I expect him to be interessted in having UML as full > featured cluster simulation tool available, and Andi because I hope he > might know the network code much better than me... > > FYI, full thread can be found for example at > http://thread.gmane.org/gmane.linux.uml.devel/4607 Paolo's analysis is basically correct. loopback sets this flag for better performance. Actually in 2.6 it probably doesn't help very much anymore because TCP can do checksum copy RX now, and that would get the checksum basically for free. But it's still there and may still make things slightly faster. If UML taps the packets from lo it will see incorrect checksums. Using a tun or ethertap device would avoid this. In the worst case you could also just delete the flag from the loopback interface, it's only an optimization. -Andi ------------------------------------------------------- This SF.net email is sponsored by: IT Product Guide on ITManagersJournal Use IT products in your business? Tell us what you think of them. Give us Your Opinions, Get Free ThinkGeek Gift Certificates! Click to find out more http://productguide.itmanagersjournal.com/guidepromo.tmpl _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel