From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Gallatin Subject: Re: [PATCH 0/4][RFC] lro: Generic Large Receive Offload for TCP traffic Date: Tue, 31 Jul 2007 09:34:35 -0400 Message-ID: <46AF3A6B.2040006@myri.com> References: <200707301724.33865.ossthema@de.ibm.com> <46AE4AC9.6060109@myri.com> <200707311233.31227.ossthema@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev , Christoph Raisch , Jan-Bernd Themann , linux-kernel , linux-ppc , Marcus Eder , Thomas Klein , Stefan Roscher , David Miller , Jeff Garzik To: Jan-Bernd Themann Return-path: Received: from dsl.myri.com ([64.172.73.26]:1937 "EHLO myri.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1759457AbXGaNe5 (ORCPT ); Tue, 31 Jul 2007 09:34:57 -0400 In-Reply-To: <200707311233.31227.ossthema@de.ibm.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Jan-Bernd Themann wrote: > On Monday 30 July 2007 22:32, Andrew Gallatin wrote: >> Second, you still need to set skb->ip_summed = CHECKSUM_UNNECESSARY >> when modified packets are flushed, else the stack will see bad >> checksums for packets from CHECKSUM_COMPLETE drivers using the >> skb interface. Fixed in the attached patch. > > I thought about it... As we do update the TCP checksum for aggregated > packets we could add a second ip_summed field in the net_lro_mgr struct > used for aggregated packets to support HW that does not have any checksum helper > functionality. These drivers could set this ip_summed field to CHECKSUM_NONE, > and thus leave the checksum check to the stack. I'm not sure if these old devices benefit > a lot from LRO. So what do you think? This might be handy, and it would also fix the problem with CHECKSUM_PARTIAL drivers using the skb interface by allowing them to set it to CHECKSUM_UNNECESSARY. >> Fourth, I did some traffic sniffing to try to figure out what's going >> on above, and saw tcpdump complain about bad checksums. Have you tried >> running tcpdump -s 65535 -vvv? Have you also seen bad checksums? >> I seem to see this for both page- and skb-based versions of the driver. >> > > Hmmm, can't confirm that. For our skb-based version I see > correct checksums for aggregated packets and for the page-based version as well. > I used: (tcpdump -i ethX -s 0 -w dump.bin) in combination with ethereal. > Don't see problems as well with your tcpdump command. I'm still trying to get a handle on this. It happens both with page based and skb based receive for me.. I would not be surprised if I was doing something wrong in myri10ge. But I don't see it without LRO, or with my LRO. I'll let you know when I figure it out.. In the meantime, in case you have any insight, I've left a capture of a small "netcat" transfer of a 64KB file full of zeros at http://www.myri.com/staff/gallatin/lro/netcat_dump.bz2 Drew