From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hisashi T Fujinaka Subject: Re: [PATCH] e1000e: Cleanup handling of VLAN_HLEN as a part of max frame size Date: Wed, 8 Apr 2015 16:05:45 -0700 (PDT) Message-ID: References: <20150408204630.4643.37880.stgit@ahduyck-vm-fedora22> <5525B2AE.80301@gmail.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Alexander Duyck , intel-wired-lan@lists.osuosl.org, jeffrey.t.kirsher@intel.com, netdev@vger.kernel.org, mike@cchtml.com To: Alexander Duyck Return-path: Received: from 75-148-87-25-Oregon.hfc.comcastbusiness.net ([75.148.87.25]:16416 "EHLO chris.i8u.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754451AbbDHXFq (ORCPT ); Wed, 8 Apr 2015 19:05:46 -0400 In-Reply-To: <5525B2AE.80301@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 8 Apr 2015, Alexander Duyck wrote: > On 04/08/2015 02:15 PM, Hisashi T Fujinaka wrote: >> On Wed, 8 Apr 2015, Alexander Duyck wrote: >> >>> Fixes: c751a3d58cf2d ("e1000e: Correctly include VLAN_HLEN when >>> changing interface MTU") >>> Signed-off-by: Alexander Duyck >>> --- >>> >>> I have only build tested this though I am 99% sure the fixes here are >>> correct. This patch should fix issues on 82573 and ich8 w/ setting >>> an MTU >>> of 1500, and for the PCH series w/ setting an MTU of 9000. >> >> Since the original fix was something submitted by Red Hat, can you check >> that you're not re-breaking whatever it was that Red Hat thought they >> were fixing? > > The original issue is referenced in the patch that this fixes. The > problem was that the VLAN header wasn't being considered when computing > the Rx buffer size, so you could change the MTU to 1504 and the if > statement at the end of e1000_change_mtu was still using a 1522 Rx > buffer size and max frame even though we had technically just configured > things for 1526. > > The updated logic is correctly taking the VLAN header into account so if > you bump the MTU 1504 it will switch over to jumbo frames mode w/ 2K > buffers. > > The bit I am fixing is that there were several spots including the > backend value for max_hw_frame_size that didn't take VLAN header length > into account. There were cases where 1500 MTU was being treated as a > jumbo frame, or we were coming up 4 bytes shy as in the pch2, ich8, and > 82573 e1000_info structures. The max_hw_frame_size should still be limited to 9018.