From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Gloudon Subject: BUG: TCPDUMP invalid cksum persists after disabling TCP cksum offload Date: Tue, 18 Sep 2012 17:14:23 -0400 Message-ID: <20120918211423.GA19115@darkstar> References: <20120918193208.GA19030@darkstar> <1347998905.2685.29.camel@bwh-desktop.uk.solarflarecom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: netdev@vger.kernel.org Return-path: Received: from mail-qa0-f53.google.com ([209.85.216.53]:40531 "EHLO mail-qa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755315Ab2IRVOa (ORCPT ); Tue, 18 Sep 2012 17:14:30 -0400 Received: by qaas11 with SMTP id s11so420246qaa.19 for ; Tue, 18 Sep 2012 14:14:29 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1347998905.2685.29.camel@bwh-desktop.uk.solarflarecom.com> Sender: netdev-owner@vger.kernel.org List-ID: Hello, I am seeing that tx checksum offload appears to be still running after disabling the feature with ethtool. I'm using kernel 3.6.0-rc6 and the latest ethtool from the git repo. The default settings on my e1000e NIC: # ethtool -k eth1 | grep ': on' rx-checksumming: on tx-checksumming: on tx-checksum-ip-generic: on scatter-gather: on tx-scatter-gather: on tcp-segmentation-offload: on tx-tcp-segmentation: on tx-tcp6-segmentation: on generic-segmentation-offload: on generic-receive-offload: on rx-vlan-offload: on tx-vlan-offload: on receive-hashing: on highdma: on [fixed] rx-vlan-filter: on [fixed] tx-nocache-copy: on The results after disabling tcp cksum offload feature: # ethtool -K eth1 tx off Actual changes: tx-checksumming: off tx-checksum-ip-generic: off scatter-gather: off tx-scatter-gather: off [requested on] tcp-segmentation-offload: off tx-tcp-segmentation: off [requested on] tx-tcp6-segmentation: off [requested on] generic-segmentation-offload: off [requested on] However, in tcpdump, I'm still observing incorrect tcp checksum: 14:44:38.838711 IP (tos 0x10, ttl 64, id 45798, offset 0, flags [DF], proto TCP (6), length 60) 1.1.1.2.59748 > 1.1.1.1.23: Flags [S], cksum 0x0433 (incorrect -> 0x4137), seq 318222122, win 14600, options [mss 1460,sackOK,TS val 5447116 ecr 0,nop,wscale 7], length 0 Is this behaviour valid? I'm quite baffled. Regards, Jamie Gloudon