Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941309AbcJYDF0 (ORCPT ); Mon, 24 Oct 2016 23:05:26 -0400 Received: from mail-pf0-f181.google.com ([209.85.192.181]:36394 "EHLO mail-pf0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932360AbcJYDFY (ORCPT ); Mon, 24 Oct 2016 23:05:24 -0400 Date: Mon, 24 Oct 2016 23:05:14 -0400 From: Jarod Wilson To: Stefan Richter Cc: "David S. Miller" , netdev@vger.kernel.org, linux1394-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next 2/2 v2] firewire: net: set initial MTU = 1500 unconditionally, fix IPv6 on some CardBus cards Message-ID: <20161025030514.GM42084@redhat.com> References: <20161019023333.15760-1-jarod@redhat.com> <20161020175524.6184-1-jarod@redhat.com> <20161020175524.6184-8-jarod@redhat.com> <20161022211606.3b5d137d@kant> <20161022212759.228c7642@kant> <20161023011824.GE32569@redhat.com> <20161023162903.4166a35d@kant> <20161023163056.6bc38610@kant> <20161024015013.GB42084@redhat.com> <20161024142613.29145f32@kant> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161024142613.29145f32@kant> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1408 Lines: 34 On Mon, Oct 24, 2016 at 02:26:13PM +0200, Stefan Richter wrote: > firewire-net, like the older eth1394 driver, reduced the initial MTU to > less than 1500 octets if the local link layer controller's asynchronous > packet reception limit was lower. > > This is bogus, since this reception limit does not have anything to do > with the transmission limit. Neither did this reduction affect the TX > path positively, nor could it prevent link fragmentation at the RX path. > > Many FireWire CardBus cards have a max_rec of 9, causing an initial MTU > of 1024 - 16 = 1008. RFC 2734 and RFC 3146 allow a minimum max_rec = 8, > which would result in an initial MTU of 512 - 16 = 496. On such cards, > IPv6 could only be employed if the MTU was manually increased to 1280 or > more, i.e. IPv6 would not work without intervention from userland. > > We now always initialize the MTU to 1500, which is the default according > to RFC 2734 and RFC 3146. > > On a VIA VT6316 based CardBus card which was affected by this, changing > the MTU from 1008 to 1500 also increases TX bandwidth by 6 %. > RX remains unaffected. > > CC: netdev@vger.kernel.org > CC: linux1394-devel@lists.sourceforge.net > CC: Jarod Wilson > Signed-off-by: Stefan Richter > --- > v2: use ETH_DATA_LEN, add comment Acked-by: Jarod Wilson -- Jarod Wilson jarod@redhat.com